Category Archives: Video Game Development

Demystifying VMT and RTTI in Unreal Engine C++

(Cover Photo: ©1984 – ITV Granada
Jeremy Brett, “Sherlock Holmes” TV Series)

It is no secret that, due to nature of modern OOP guidelines, Unreal Engine C++ source code is full of “virtual functions”. It is also no secret that, calling a virtual function is inherently slower than calling a non-virtual function… So, what’s the catch?

A non-virtual call is simply a jump (JMP) to a compiled-in pointer. On the other hand, a virtual call requires at least an extra indexed dereference, and sometimes a fixup addition, which is stored in a lookup table known as Virtual Method Table (VMT). This is simply why a virtual call is always slower than a non-virtual call.

To avoid this overhead, compilers usually steer clear of VMT whenever the call can be resolved at compile time. However, due to complex nature of Inheritence based class structures used in modern game engines, using VMT is unavoidable in most cases.

Virtual Method Table (VMT)

An object’s VMT (also known as vtable) contains the addresses of the object’s dynamically bound methods. Method calls are performed by fetching the method’s address from the object’s virtual method table.

C++ compiler creates a separate VMT for each class. When an object is created, a virtual pointer (VPTR) to this table is added as a hidden member of this object. The compiler also generates hidden code in the constructors of each class to initialize new object’s VPTR to the address of its class’ virtual method table.

The virtual method table is same for all objects belonging to the same class, and is therefore typically shared between them. Objects belonging to type-compatible classes in an inheritance hierarchy will have virtual method tables with the same layout.

Tip: The C++ standards do not mandate exactly how dynamic dispatch must be implemented, but compilers generally use minor variations on the same basic model. The VMT is generally a good performance trade-off to achieve dynamic dispatch, but there are alternatives, such as Binary Tree Dispatch (BTD), with higher performance but different costs.

Speaking of hidden codes and VMTs in the constructors of each class, each C++ object should also contain additional information about its type. An object’s data type is a crucial information in terms of casting.

Run-Time Type Information  (RTTI)

RTTI is a feature of the C++ programming language that exposes information about an object’s data type at runtime. It can apply to simple data types, such as integers and characters, or to generic types.

Run-Time Type Information is available only for classes that are polymorphic, which means they have at least one virtual method. In practice, this is not a limitation because base classes must have a virtual destructor to allow objects of derived classes to perform proper cleanup if they are deleted from a base pointer.

RTTI is used in three main C++ language elements:

  The dynamic_cast operator: Used for conversion of polymorphic types.

  The typeid operator: Used for identifying the exact type of an object.

  The type_info class: Used to hold the type information returned by the typeid operator.

In order to perform cast-related operations listed above, RTTI heavily uses VMT. For example, given an object of a polymorphic class, a type_info object can be obtained through the use of the typeid operator.  In principle, this is a simple operation which involves finding the VMT, through that finding the most-derived class object of which the object is part, and then extracting a pointer to the type_info object from that object’s virtual function table (or equivalent).

In terms of performance, using the dynamic_cast operator is more expensive than type_info. Given a pointer to an object of a polymorphic class, a cast to a pointer to another base subobject of the same derived class object can be done using a dynamic_cast.  In principle, this operation involves finding the VMT, through that finding the most-derived class object of which the object is part, and then using type information associated with that object to determine if the conversion (cast) is allowed, and finally performing any required adjustments of the pointer.  In principle, this checking involves the traversal of a data structure describing the base classes of the most derived class.  Thus, the run-time cost of a dynamic_cast may depend on the relative positions in the class hierarchy of the two classes involved.

Tip: In the original C++ design, Bjarne Stroustrup did not include RTTI, because he thought this mechanism was often misused.

Hacking VMT and RTTI Information using UE C++

In order to gather “header” information (that contains VMT and RTTI data) in an Unreal Engine C++ class/object, I have written the following LogClassHeader() C++ function using Visual Studio 2019 version 16.3.8 for Unreal Engine version 4.23.1.

void UDebugCore::LogClassHeader(void* const pThis, size_t nSize)
{
  FString fsClassName = "NULL";
  FString fsObjectName = "NULL";
  UObject* const pCastedToUObject = (UObject*)(pThis);
  void** const pCastedToHeader = reinterpret_cast<void**>(pThis);

  if (pCastedToUObject)
  {
    fsClassName = pCastedToUObject->GetClass()->GetName();
    fsObjectName = pCastedToUObject->GetName();
  }

  if (pCastedToHeader)
  {
    for (size_t i = 0; i < nSize / sizeof(void*); i++)
    {
      MACRO_PRINTF("Pointer[%04zu] = 0x%p", i, pCastedToHeader[i])
    }
  }
}

This function has 2 input parameters:

  pThis:  Object to extract Class Header Info from
  nSize:  Size of Header

Calling the function is very easy. You simply insert your call into the constructor of the class that you would like to hack. For example, the following code gathers C++ header information of <APlayerControllerThirdPerson> class.

APlayerControllerThirdPerson::APlayerControllerThirdPerson()
{
  UDebugCore::LogClassHeader(this, sizeof(*this));
}

When you run the code, all pointers that are available (and used) in the header of <APlayerControllerThirdPerson> will be listed. And, in case you need, instance name and class type is stored in fsObjectName and fsClassName variables, as a bonus.

Pointer[0000] = 0x00007FFC8A3ECB00
Pointer[0001] = 0x0000BC5B00000231
Pointer[0002] = 0x000001648346AC00
Pointer[0003] = 0x000AAD5B000AAD5B
Pointer[0004] = 0x0000000000000000
Pointer[0005] = 0x00000164834864E0
Pointer[0006] = 0x00007FFCAAB2EF98
Pointer[0007] = 0x00007FFCA8708208
Pointer[0008] = 0x0000000F00000000
            .....
             ...
              .

So, what do these numbers mean? Well, all these pointers are addresses of the virtual functions, followed by some of the member variables. In order to understand which is which, we need to decipher the structure of the data set.

Here comes the tricky part! With each and every update to Visual Studio C++ compiler, the structure tends to get updated as well. In other words, the header structure of a C++ class changes with each major compiler update. Try to think of it as a “living organism”. As I’m typing this sentence now, a new update with a new C++ header structure may be on its way. So, it is up to you (!) to analyze what’s going on under the hood.

Good news is, we can gather <template> information about C++ class header structure from the official Microsoft patent documents! Although they are not up-to-date, I think it is a good practice to start the investigation using the source of information itself.

Here is some of the Microsoft patents which describe various parts of C++ implementation used in Visual Studio:

  US Patent #5410705: “Method for generating an object data structure layout for a class in a compiler for an object-oriented programming language”

  US Patent #5617569: “Method and system for implementing pointers to members in a compiler for an object-oriented programming language”

  US Patent #5754862: “Method and system for accessing virtual base classes”

  US Patent #5297284: “Method and system for implementing virtual functions and virtual base classes and setting a this pointer for an object-oriented programming language”

  US Patent #5371891: “Method for object construction in a compiler for an object-oriented programming language”

  US Patent #5603030: “Method and system for destruction of objects using multiple destructor functions in an object-oriented computer system”

So, what I’m offering is, good old-fashioned reverse engineering”.

– “Is such a challenge worth it?”

– “Um, yes!… If it doesn’t break you, it can make you.”

References:

  Bjarne Stroustrup, “A History of C++: 1979—1991”, p. 50 – (March 1993)

  Keith Cooper & Linda Torczon, “Engineering A Compiler”, Morgan Kaufmann, 2nd Edition – (2011)

  Microsoft Visual Studio Documentation, “C++ Run-Time Type Information” – (November 2016)

  “Technical Report on C++ Performance”, OpenRCE.org – (September 2006)

  “Reversing Microsoft Visual C++: Classes, Methods and RTTI”, OpenRCE.org – (September 2006)

  “Intel® 64 and IA-32 Architectures Optimization Reference Manual” – (April 2018)

Captured Moments 2018

(Cover Photo:  © www.yukokusamurai.com)

When I appreciate ‘the moment’, happiness follows. Happiness is often in the little things, and year 2018 has offered me a bunch of them. Sincerely thankful and grateful for all the little things I have been given this year… Now is the time to cherish the ‘moments of joy’ by sharing a few snapshots, in no particular order.

Unreal Fest Europe 2018

A three day event designed exclusively for game creators using Unreal Engine, with speakers drawn from Epic, platform owners and some of the leading development studios in Europe took place in Berlin, April 24-27. Such a great opportunity for meeting old friends,  and making new ones. – Thank you Epic!

© 2018 – All event photos by Saskia Uppenkamp

A Visit to NERD

It is no secret that Nintendo is using Unreal Engine 4 for their current and upcoming line of Switch games. As an Unreal Engine developer, I had the privilege of visiting Nintendo European Research & Development (NERD) in Paris for a 1-on-1 meeting. Due to usual Nintendo regulations, I’m not allowed to share any kind of information about the top-notch engineering stuff that I had witnessed, but that can’t prevent me from telling you how much I was impressed. All I can say is “WOW!” 😉

I have great admiration and respect for Japanese business culture, which is genuinely represented in Paris. Thank you very much for your kind hospitality!

IndieCade Europe 2018

IndieCade continues to support the development of independent games by organizing a series of international events to promote the future of indie games. This year, we had the 3rd installment of European organization, and it is getting better and bigger each year. I love the indie spirit. No matter how experienced you are, we always have new things to learn from each other.

From my perspective, the most iconic moment of the event was meeting and chatting with Japanese game developer Hidetaka Suehiro (aka “Swery65”), the designer of The Last Blade (1997) and The Last Blade 2 (1998). Both games were released by SNK for Neo Geo MVSmy all time favourite 2D console.

So, guess what we talked about… Fighting games? No… Neo Geo? No… Game design? No… Believe it or not, our main topic was “best hookah (water pipe) cafés in Istanbul”. I’m simply amazed to discover that he knows Istanbul better than me. Swery65 is full of surprises!

mini-RAAT Meetings @ MakerEvi

Try to imagine an unscheduled last-minute “members only” meeting, hosting crème de la crème IT professionals ranging from ex-Microsoft engineers to gifted video game artists, acclaimed musicians, network specialists, and many other out of this world talents, in addition to a bunch of academicians with hell of titles and degrees! So, what on earth is the common denominator that brings these gentlemen together, at least once or twice a year? Retrocomputing, for sure… Bundled with fun, laughter and joy! 🙂

© 2018 – All event photos by Alcofribas

Special thanks to our host, MakerEvi – a professional ‘Maker Movement Lab’ dedicated to contemporary DIY culture, fueled by the artisan spirit and kind hospitality of The Gürevins. An exceptional blend of local perspective and global presence.

Dila’s Graduation

This year, my dear daughter has graduated from Collège Sainte Pulchérie YN2000 with DELF B1 level French diploma, a compulsory certificate to follow studies in the French higher education system. Being a hardworking student, she has passed national high school entrance exam, and is currently attending Lycée Français Saint-Michel. – “I am proud of you… Bonne chance, ma chérie!”

“The bond that links your true family is not one of blood,
but of respect and joy in each other’s life.”
– Richard Bach

Family is a ‘sanctuary’ for the individual. If we are blessed enough to have a loving, happy, and peaceful family, we should be grateful every day for it. It is where we learn to feel the value of being part of something greater than ourselves. Love is a powerful thing; we just have to be open to it.

Life is a Celebration

For all the moments I have enjoyed and to all my dear friends & members of my family who made those meaningful moments possible, I would like to propose a toast. Would you like to join me for a glass of absinthe, so that we keep on chasing our ‘green fairies’ together and forever? 😉

Taming a Beast: CPU Cache

(Cover Photo:  © Granger – “Lion Tamer”
The American animal tamer Clyde Beatty
performing in the 1930s.)

The processor’s caches are for the most part transparent to software. When enabled, instructions and data flow through these caches without the need for explicit software control. However, knowledge of the behavior of these caches may be useful in optimizing software performance. If not tamed wisely, these innocent cache mechanisms can certainly be a headache for novice C/C++ programmers.

First things first… Before I start with example C/C++ codes showing some common pitfalls and urban caching myths that lead to hard-to-trace bugs, I would like to make sure that we are all comfortable with ‘cache related terms’.

Terminology

In theory, CPU cache is a very high speed type of memory that is placed between the CPU and the main memory. (In practice, it is actually inside the processor, mostly operating at the speed of the CPU.) In order to improve latency of fetching information from the main memory, cache stores some of the information temporarily so that the next access to the same chunk of information is faster. CPU cache can store both ‘executable instructions’ and ‘raw data’.

“… from cache, instead of going back to memory.”

When the processor recognizes that an information being read from memory is cacheable, the processor reads an entire cache line into the appropriate cache slot (L1, L2, L3, or all). This operation is called a cache line fill. If the memory location containing that information is still cached when the processor attempts to access to it again, the processor can read that information from the cache instead of going back to memory. This operation is called a cache hit.

Hierarchical Cache Structure of the Intel Core i7 Processors

When the processor attempts to write an information to a cacheable area of memory, it first checks if a cache line for that memory location exists in the cache. If a valid cache line does exist, the processor (depending on the write policy currently in force) can write that information into the cache instead of writing it out to system memory. This operation is called a write hit. If a write misses the cache (that is, a valid cache line is not present for area of memory being written to), the processor performs a cache line fill, write allocation. Then it writes the information into the cache line and (depending on the write policy currently in force) can also write it out to memory. If the information is to be written out to memory, it is written first into the store buffer, and then written from the store buffer to memory when the system bus is available.

“… cached in shared state, between multiple CPUs.”

When operating in a multi-processor system, The Intel 64 and IA-32 architectures have the ability to keep their internal caches consistent both with system memory and with the caches in other processors on the bus. For example, if one processor detects that another processor intends to write to a memory location that it currently has cached in shared state, the processor in charge will invalidate its cache line forcing it to perform a cache line fill the next time it accesses the same memory location. This type of internal communication between the CPUs is called snooping.

And finally, translation lookaside buffer (TLB) is a special type of cache designed for speeding up address translation for virtual memory related operations. It is a part of the chip’s memory-management unit (MMU). TLB keeps track of where virtual pages are stored in physical memory, thus speeds up ‘virtual address to physical address’ translation by storing a lookup page-table.

So far so good… Let’s start coding, and shed some light on urban caching myths. 😉

 

 

How to Guarantee Caching in C/C++

To be honest, under normal conditions, there is absolutely no way to guarantee that the variable you defined in C/C++ will be cached. CPU cache and write buffer management are out of scope of the C/C++ language, actually.

Most programmers assume that declaring a variable as constant will automatically turn it into something cacheable!

const int nVar = 33;

As a matter of fact, doing so will tell the C/C++ compiler that it is forbidden for the rest of the code to modify the variable’s value, which may or may not lead to a cacheable case. By using a const, you simply increase the chance of getting it cached. In most cases, compiler will be able to turn it into a cache hit. However, we can never be sure about it unless we debug and trace the variable with our own eyes.

 

 

How to Guarantee No Caching in C/C++

An urban myth states that, by using volatile type qualifier, it is possible to guarantee that a variable can never be cached. In other words, this myth assumes that it might be possible to disable CPU caching features for specific C/C++ variables in your code!

volatile int nVar = 33;

Actually, defining a variable as volatile prevents compiler from optimizing it, and forces the compiler to always refetch (read once again) the value of that variable from memory. But, this may or may not prevent it from caching, as volatile has nothing to do with CPU caches and write buffers, and there is no standard support for these features in C/C++.

So, what happens if we declare the same variable without const or volatile?

int nVar = 33;

Well, in most cases, your code will be executed and cached properly. (Still not guaranteed though.) But, one thing for sure… If you write ‘weird’ code, like the following one, then you are asking for trouble!

int nVar = 33;
while (nVar == 33)
{
   . . .
}

In this case, if the optimization is enabled, C/C++ compiler may assume that nVar never changes (always set to 33) due to no reference of nVar in loop’s body, so that it can be replaced with true for the sake of optimizing while condition.

while (true)
{
   . . .
}

A simple volatile type qualifier fixes the problem, actually.

volatile int nVar = 33;

 

 

What about Pointers?

Well, handling pointers is no different than taking care of simple integers.

Case #1:

Let’s try to evaluate the while case mentioned above once again, but this time with a Pointer.

int nVar = 33;
int *pVar = (int*) &nVar;
while (*pVar)
{
   . . .
}

In this case,

  nVar is declared as an integer with an initial value of 33,
  pVar is assigned as a Pointer to nVar,
  the value of nVar (33) is gathered using pointer pVar, and this value is used as a conditional statement in while loop.

On the surface there is nothing wrong with this code, but if aggressive C/C++ compiler optimizations are enabled, then we might be in trouble. – Yes, some compilers are smarter than others! 😉

Due to fact that the value of pointer variable has never been modified and/or accessed through the while loop, compiler may decide to optimize the frequently called conditional statement of the loop. Instead of fetching *pVar (value of nVar) each time from the memory, compiler might think that keeping this value in a register might be a good idea. This is known as ‘software caching’.

Now, we have two problems here:

1.) Values in registers are ‘hardware cached’. (CPU cache can store both instructions and data, remember?) If somehow, software cached value in the register goes out of sync with the original one in memory, the CPU will never be aware of this situation and will keep on caching the old value from hardware cache. – CPU cache vs software cache. What a mess!

Tip: Is that scenario really possible?! – To be honest, no. During the compilation process, the C/C++ compiler should be clever enough to foresee that problem, if-and-only-if *pVar has never been modified in loop’s body. However, as a programmer, it is our responsibility to make sure that compiler should be given ‘properly written code’ with no ambiguous logic/data treatment. So, instead of keeping our fingers crossed and expecting miracles from the compiler, we should take complete control over the direction of our code. Before making assumptions on how our code will be compiled, we should first make sure that our code is crystal clear.

2.) Since the value of nVar has never been modified, the compiler can even go one step further by assuming that the check against *pVar can be casted to a Boolean value, due to its usage as a conditional statement. As a result of this optimization, the code above might turn into this:

int nVar = 33;
int *pVar = (int*) &nVar;

if (*pVar)
{
   while (true)
   {
      . . .
   }
}

Both problems detailed above, can be fixed by using a volatile type qualifier. Doing so prevents the compiler from optimizing *pVar, and forces the compiler to always refetch the value from memory, rather than using a compiler-generated software cached version in registers.

int nVar = 33;
volatile int *pVar = (int*) &nVar;
while (*pVar)
{
   . . .
}

Case #2:

Here comes an another tricky example about Pointers.

const int nVar = 33;
int *pVar = (int*) &nVar;
*pVar = 0;

In this case,

  nVar is declared as a ‘constant’ variable,
  pVar is assigned as a Pointer to nVar,
  and, pVar is trying to change the ‘constant’ value of nVar!

Under normal conditions, no C/C++ programmer would make such a mistake, but for the sake of clarity let’s assume that we did.

If aggressive optimization is enabled, due to fact that;

a.) Pointer variable points to a constant variable,

b.) Value of pointer variable has never been modified and/or accessed,

some compilers may assume that the pointer can be optimized for the sake of software caching. So, despite *pVar = 0, the value of nVar may never change.

Is that all? Well, no… Here comes the worst part! The value of nVar is actually compiler dependent. If you compile the code above with a bunch of different C/C++ compilers, you will notice that in some of them nVar will be set to 0, and in some others set to 33 as a result of ‘ambiguous’ code compilation/execution. Why? Simply because, every compiler has its own standards when it comes to generating code for ‘constant’ variables. As a result of this inconsistent situation, even with just a single constant variable, things can easily get very complicated.

Tip: The best way to fix ‘cache oriented compiler optimization issues’, is to change the way you write code, with respect to tricky compiler specific optimizations in mind. Try to write crystal clear code. Never assume that compiler knows programming better than you. Always debug, trace, and check the output… Be prepared for the unexpected!

Fixing such brute-force compiler optimization issues is quite easy. You can get rid of const type qualifier,

const int nVar = 33;

or, replace const with volatile type qualifier,

volatile int nVar = 33;

or, use both!

const volatile int nVar = 33;
Tip: ‘const volatile’ combination is commonly used on embedded systems, where hardware registers that can be read and are updated by the hardware, cannot be altered by software. In such cases, reading hardware register’s value is never cached, always refetched from memory.

 

 

Rule of Thumb

Using volatile is absolutely necessary in any situation where compiler could make wrong assumptions about a variable keeping its value constant, just because a function does not change it itself. Not using volatile would create very complicated bugs due to the executed code that behaves as if the value did not change – (It did, indeed).

If code that works fine, somehow fails when you;

  Use cross compilers,
  Port code to a different compiler,
  Enable compiler optimizations,
  Enable interrupts,

make sure that your compiler is NOT over-optimizing variables for the sake of software caching.

Please keep in mind that, volatile has nothing to do with CPU caches and write buffers, and there is no standard support for these features in C/C++. These are out of scope of the C/C++ language, and must be solved by directly interacting with the CPU core!

 

 

Getting Hands Dirty via Low-Level CPU Cache Control

Software driven hardware cache management is possible. There are special ‘privileged’ Assembler instructions to clean, invalidate, flush cache(s), and synchronize the write buffer. They can be directly executed from privileged modes. (User mode applications can control the cache through system calls only.) Most compilers support this through built-in/intrinsic functions or inline Assembler.

The Intel 64 and IA-32 architectures provide a variety of mechanisms for controlling the caching of data and instructions, and for controlling the ordering of reads/writes between the processor, the caches, and memory.

These mechanisms can be divided into two groups:

  Cache control registers and bits: The Intel 64 and IA-32 architectures define several dedicated registers and various bits within control registers and page/directory-table entries that control the caching system memory locations in the L1, L2, and L3 caches. These mechanisms control the caching of virtual memory pages and of regions of physical memory.

  Cache control and memory ordering instructions: The Intel 64 and IA-32 architectures provide several instructions that control the caching of data, the ordering of memory reads and writes, and the prefetching of data. These instructions allow software to control the caching of specific data structures, to control memory coherency for specific locations in memory, and to force strong memory ordering at specific locations in a program.

How does it work?

The Cache Control flags and Memory Type Range Registers (MTRRs) operate hierarchically for restricting caching. That is, if the CD flag of control register 0 (CR0) is set, caching is prevented globally. If the CD flag is clear, the page-level cache control flags and/or the MTRRs can be used to restrict caching.

Tip: The memory type range registers (MTRRs) provide a mechanism for associating the memory types with physical-address ranges in system memory. They allow the processor to optimize operations for different types of memory such as RAM, ROM, frame-buffer memory, and memory-mapped I/O devices. They also simplify system hardware design by eliminating the memory control pins used for this function on earlier IA-32 processors and the external logic needed to drive them.

If there is an overlap of page-level and MTRR caching controls, the mechanism that prevents caching has precedence. For example, if an MTRR makes a region of system memory uncacheable, a page-level caching control cannot be used to enable caching for a page in that region. The converse is also true; that is, if a page-level caching control designates a page as uncacheable, an MTRR cannot be used to make the page cacheable.

In cases where there is a overlap in the assignment of the write-back and write-through caching policies to a page and a region of memory, the write-through policy takes precedence. The write-combining policy -which can only be assigned through an MTRR or Page Attribute Table (PAT)– takes precedence over either write-through or write-back. The selection of memory types at the page level varies depending on whether PAT is being used to select memory types for pages.

Tip: The Page Attribute Table (PAT) extends the IA-32 architecture’s page-table format to allow memory types to be assigned to regions of physical memory based on linear address mappings. The PAT is a companion feature to the MTRRs; that is, the MTRRs allow mapping of memory types to regions of the physical address space, where the PAT allows mapping of memory types to pages within the linear address space. The MTRRs are useful for statically describing memory types for physical ranges, and are typically set up by the system BIOS. The PAT extends the functions of the PCD and PWT bits in page tables to allow all five of the memory types that can be assigned with the MTRRs (plus one additional memory type) to also be assigned dynamically to pages of the linear address space.

 

 

CPU Control Registers

Generally speaking, control registers (CR0, CR1, CR2, CR3, and CR4) determine operating mode of the processor and the characteristics of the currently executing task. These registers are 32 bits in all 32-bit modes and compatibility mode. In 64-bit mode, control registers are expanded to 64 bits.

The MOV CRn instructions are used to manipulate the register bits. These instructions can be executed only when the current privilege level is 0.

Instruction 64-bit Mode Legacy Mode Description
MOV r32, CR0–CR7 Valid Move control register to r32.
MOV r64, CR0–CR7 Valid Move extended control register to r64.
MOV r64, CR8 Valid Move extended CR8 to r64.
MOV CR0–CR7, r32 Valid Move r32 to control register.
MOV CR0–CR7, r64 Valid Move r64 to extended control register.
MOV CR8, r64 Valid Move r64 to extended CR8.
Tip: When loading control registers, programs should not attempt to change the reserved bits; that is, always set reserved bits to the value previously read. An attempt to change CR4’s reserved bits will cause a general protection fault. Reserved bits in CR0 and CR3 remain clear after any load of those registers; attempts to set them have no impact.

The Intel 64 and IA-32 architectures provide the following cache-control registers and bits for use in enabling or restricting caching to various pages or regions in memory:

  CD flag (bit 30 of control register CR0): Controls caching of system memory locations. If the CD flag is clear, caching is enabled for the whole of system memory, but may be restricted for individual pages or regions of memory by other cache-control mechanisms. When the CD flag is set, caching is restricted in the processor’s caches (cache hierarchy) for the P6 and more recent processor families. With the CD flag set, however, the caches will still respond to snoop traffic. Caches should be explicitly flushed to insure memory coherency. For highest processor performance, both the CD and the NW flags in control register CR0 should be cleared. To insure memory coherency after the CD flag is set, the caches should be explicitly flushed. (Setting the CD flag for the P6 and more recent processor families modify cache line fill and update behaviour. Also, setting the CD flag on these processors do not force strict ordering of memory accesses unless the MTRRs are disabled and/or all memory is referenced as uncached.)

  NW flag (bit 29 of control register CR0): Controls the write policy for system memory locations. If the NW and CD flags are clear, write-back is enabled for the whole of system memory, but may be restricted for individual pages or regions of memory by other cache-control mechanisms.

  PCD and PWT flags (in paging-structure entries): Control the memory type used to access paging structures and pages.

  PCD and PWT flags (in control register CR3): Control the memory type used to access the first paging structure of the current paging-structure hierarchy.

  G (global) flag in the page-directory and page-table entries: Controls the flushing of TLB entries for individual pages.

  PGE (page global enable) flag in control register CR4: Enables the establishment of global pages with the G flag.

  Memory type range registers (MTRRs): Control the type of caching used in specific regions of physical memory.

  Page Attribute Table (PAT) MSR: Extends the memory typing capabilities of the processor to permit memory types to be assigned on a page-by-page basis.

  3rd Level Cache Disable flag (bit 6 of IA32_MISC_ENABLE MSR): Allows the L3 cache to be disabled and enabled, independently of the L1 and L2 caches. (Available only in processors based on Intel NetBurst microarchitecture)

  KEN# and WB/WT# pins (Pentium processor): Allow external hardware to control the caching method used for specific areas of memory. They perform similar (but not identical) functions to the MTRRs in the P6 family processors.

  PCD and PWT pins (Pentium processor): These pins (which are associated with the PCD and PWT flags in control register CR3 and in the page-directory and page-table entries) permit caching in an external L2 cache to be controlled on a page-by-page basis, consistent with the control exercised on the L1 cache of these processors. (The P6 and more recent processor families do not provide these pins because the L2 cache is embedded in the chip package.)

 

 

How to Manage CPU Cache using Assembly Language

The Intel 64 and IA-32 architectures provide several instructions for managing the L1, L2, and L3 caches. The INVD and WBINVD instructions are privileged instructions and operate on the L1, L2 and L3 caches as a whole. The PREFETCHh, CLFLUSH and CLFLUSHOPT instructions and the non-temporal move instructions (MOVNTI, MOVNTQ, MOVNTDQ, MOVNTPS, and MOVNTPD) offer more granular control over caching, and are available to all privileged levels.

The INVD and WBINVD instructions are used to invalidate the contents of the L1, L2, and L3 caches. The INVD instruction invalidates all internal cache entries, then generates a special-function bus cycle that indicates that external caches also should be invalidated. The INVD instruction should be used with care. It does not force a write-back of modified cache lines; therefore, data stored in the caches and not written back to system memory will be lost. Unless there is a specific requirement or benefit to invalidating the caches without writing back the modified lines (such as, during testing or fault recovery where cache coherency with main memory is not a concern), software should use the WBINVD instruction.

In theory, WBINVD instruction performs the following steps:

WriteBack(InternalCaches);
Flush(InternalCaches);
SignalWriteBack(ExternalCaches);
SignalFlush(ExternalCaches);
Continue;

The WBINVD instruction first writes back any modified lines in all the internal caches, then invalidates the contents of both the L1, L2, and L3 caches. It ensures that cache coherency with main memory is maintained regardless of the write policy in effect (that is, write-through or write-back). Following this operation, the WBINVD instruction generates one (P6 family processors) or two (Pentium and Intel486 processors) special-function bus cycles to indicate to external cache controllers that write-back of modified data followed by invalidation of external caches should occur. The amount of time or cycles for WBINVD to complete will vary due to the size of different cache hierarchies and other factors. As a consequence, the use of the WBINVD instruction can have an impact on interrupt/event response time.

The PREFETCHh instructions allow a program to suggest to the processor that a cache line from a specified location in system memory be prefetched into the cache hierarchy.

The CLFLUSH and CLFLUSHOPT instructions allow selected cache lines to be flushed from memory. These instructions give a program the ability to explicitly free up cache space, when it is known that cached section of system memory will not be accessed in the near future.

The non-temporal move instructions (MOVNTI, MOVNTQ, MOVNTDQ, MOVNTPS, and MOVNTPD) allow data to be moved from the processor’s registers directly into system memory without being also written into the L1, L2, and/or L3 caches. These instructions can be used to prevent cache pollution when operating on data that is going to be modified only once before being stored back into system memory. These instructions operate on data in the general-purpose, MMX, and XMM registers.

 

 

How to Disable Hardware Caching

To disable the L1, L2, and L3 caches after they have been enabled and have received cache fills, perform the following steps:

1.) Enter the no-fill cache mode. (Set the CD flag in control register CR0 to 1 and the NW flag to 0.

2.) Flush all caches using the WBINVD instruction.

3.) Disable the MTRRs and set the default memory type to uncached or set all MTRRs for the uncached memory type.

The caches must be flushed (step 2) after the CD flag is set to insure system memory coherency. If the caches are not flushed, cache hits on reads will still occur and data will be read from valid cache lines.
The intent of the three separate steps listed above address three distinct requirements:

a.) Discontinue new data replacing existing data in the cache,

b.) Ensure data already in the cache are evicted to memory,

c.) Ensure subsequent memory references observe UC memory type semantics. Different processor implementation of caching control hardware may allow some variation of software implementation of these three requirements.

Setting the CD flag in control register CR0 modifies the processor’s caching behaviour as indicated, but setting the CD flag alone may not be sufficient across all processor families to force the effective memory type for all physical memory to be UC nor does it force strict memory ordering, due to hardware implementation variations across different processor families. To force the UC memory type and strict memory ordering on all of physical memory, it is sufficient to either program the MTRRs for all physical memory to be UC memory type or disable all MTRRs.

Tip: For the Pentium 4 and Intel Xeon processors, after the sequence of steps given above has been executed, the cache lines containing the code between the end of the WBINVD instruction and before the MTRRS have actually been disabled may be retained in the cache hierarchy. Here, to remove code from the cache completely, a second WBINVD instruction must be executed after the MTRRs have been disabled.

 

 

References:

  Richard Blum, “Professional Assembly Language”, Wrox Publishing – (2005)

  Keith Cooper & Linda Torczon, “Engineering A Compiler”, Morgan Kaufmann, 2nd Edition – (2011)

  Alexey Lyashko, “Mastering Assembly Programming”, Packt Publishing Limited – (2017)

  “Intel® 64 and IA-32 Architectures Optimization Reference Manual” – (April 2018)

  “Intel® 64 and IA-32 Architectures Software Developer’s Manual: Basic Architecture” – (November 2018)

  “Intel® 64 and IA-32 Architectures Software Developer’s Manual: Instruction Set Reference A-Z” – (November 2018)

  “Intel® 64 and IA-32 Architectures Software Developer’s Manual: System Programming Guide” – (November 2018)

  “Intel® 64 and IA-32 Architectures Software Developer’s Manual: Model-Specific Registers” – (November 2018)

 

A Warm Autumn Breeze at IndieCade Europe 2017

On the 30th of October at 08:15, the courtyard of Conservatoire National des Arts et Métiers (CNAM) was softly lit by a heart-warming morning sun, occluded by grey Parisien clouds. Just like a cool Morrissey tune; no rain, no cold, no rush. Pure tranquility… At the womb of Art and Science, I somehow felt at home.

As I was wandering around the registration tent and looking at the statues of worldwide known scientists, I bumped into an elderly British gentleman, who was also wandering around alone. We looked at each other for a moment. With a gentle smile, I said “Good morning Mr. Livingstone. Such a great pleasure meeting you, again, Sir!”. As I reminded him who I was, we instantly started talking about the good-old days at Core Design (Derby), and the heydays of 8/16-bit video game development in UK for sure. – What a privilege! For a moment, I thought time stood still.

As the chit-chat and laughter started to peak, I have noticed that we were surrounded by a bunch of young game developers, carefully listening to Mr. Ian Livingstone… Well, it’s quite normal. One does not simply bump into ‘a living legend’ everyday!

Révérence!

Sir Ian Livingstoneyes, he has been knighted once or twice!– is one of the founding fathers of the UK games industry. He is the co-creator of Dungeons & Dragons RPG franchise, author of Fighting Fantasy RPG books, game designer and board member of Domark, co-founder and chairman of Eidos (the company that acquired Core Design and started the Lara Croft:Tomb Raider franchise), and winner of a BAFTA Special Award! In the Wired 100 list for 2012, he was ranked the 16th most influential person in the UK’s digital economy… Now, you know what I mean by ‘a living legend’.

When he asked what I had been doing nowadays, I replied with a witty smile: “Nothing new. Same video game development thing for the last 32 years, Sir!”. We all laughed. He pointed at me and said “Look, we have a newcomer here!”. We all laughed, again… As he kindly looked into my eyes, I knew he was going to switch to something serious: “You know what, after all those years it’s time to start your own company, Mert!”. I gently bowed, and replied “One day I certainly will. Thank you, Sir! For now, I would like to keep on freelancing as much as I can”. He kindly nodded and smiled, as no one in the video game business knows the meaning of ‘freedom’ better than him. I thanked him again for his kind advice and understanding.

When the conversion was over, I felt like I was blessed by the God of video game business. I was relieved to see everything I have done in 3 decades was approved with a gentle nod. That means a lot to me. Relieved, by all means. – (Now, what would you call that; coincidence or destiny?)

The funny thing is, right after the conversation, I realized how young developers were strangely looking at me while whispering to each other: “Well then, who the hell is this long-haired mortal punk chit-chatting with the almighty Sir Livingstone?!” 🙂

Keynotes and Performances

Featuring two days of talks around creative industries, community support, and tools & technologies, there was something for everyone, from experienced designers and veteran artists to folks just getting started.

For me, the highlights of the meetings were;

  “Life is a Game” – Ian Livingstone
  “How Not To Kill Your Art Director” – Vincent Gault
  “How Not to Go Bankrupt” – Cliff Harris
  “The Late Game” – Brie Code

All meetings were held at the authentic Conservatoire National des Arts et Métiers (CNAM) amphitheatres, the largest of which can accomodate an audience of 750. These amphitheatres are still heavily used today, as CNAM offers a doctoral degree-granting higher education establishment and Grande école in engineering, operated by the French government, dedicated to providing education and conducting research for the promotion of science and industry. It is a continuing education school for adults seeking engineering (multidisciplinary scientific program) and business degrees, proposing evening classes in a variety of topics.

Show & Tell Demo Area

It was certainly worth visiting each and every indie game developer at the demo area. Bringing young talents and industry veterans together is a step forward for developing better games. We learn from each other. No matter how experienced you are in the global game development industry, there is (and will always be) more to learn. It is in the nature of video game development business.

On the Way Home…

After 2 days full of playing games, meeting game developers and attending various game related events, it was time to go home – yep, for game development! The thing is, I wasn’t aware of the surprise waiting for me at Paris Charles de Gaulle Airport.

Even more games!!! 🙂

In case you wonder, here is the full list of locations you can play Sony PlayStation 4 games -free of charge- at Paris CDG Airport.

  Terminal 1: Satellites 1, 3, 4, 5, 6 and 7
  Terminal 2: Gates A39, C85, D40 and D66
  Terminal 2E: Hall K Gates K36, K43 and K49
  Terminal 2E: Hall L Gates L22, L25 and L45
  Terminal 2E: Hall M Gates M25 and M45
  Terminal 2F: Gates F22 and F46
  Terminal 3: International boarding lounge

Blood, Sweat, and Pixels

Nowadays, I’m reading a tiny HarperCollins book called “Blood, Sweat, and Pixels”, written by Jason Schreier.

It is a journey through ‘development hell’ – a media industry jargon for a project that remains in development (often moving between different crews, scripts, or studios) without progressing to completion. In other words, ‘a never-ending project’.

So, if you have ever wondered what it takes to be a video game developer, don’t read this book! It must be the very last introductory document you should be referring to. – Just kidding! 😉

“If I ascend up into heaven, you are there: if I make my bed in hell, behold, you are there.” – (Psalm 139:8)

Jason Schreier takes readers on a fascinating odyssey behind the scenes of video game development. Ultimately, a tribute to the dedicated diehards and unsung heroes who scale mountains of obstacles in their quests to create the best games imaginable.

Life is hard for video game developers. Very hard, indeed… Thanks to nice small touches and heavenly surprises, life is more bearable. This book is certainly one of them. Thank you Jason!

Back to coding… 😉

New Video Game Project: Annual Information Update 2015

December 1, 2013 marks the beginning of my new video game project. The math is simple; I have been working on it for 2 years, precisely. Designing, developing and co-producing… A lot of work has been done, and many more still in progress. All tough tasks. Mostly game design related, such as 3-bit node graph architecture. Plus, a lot of coding…

It has been a busy year, indeed. – So, what’s new?

Workflow 3.0

The most distinguishing element of this project –optimized game development workflow– has been upgraded to version 3. This is something that I’m really proud of. Simply because, it is;

 more cost- and time-efficient,

more artwork/cinematography oriented,

 100% compatible with both old & next-gen workflows.

This year, I mostly concentrated on the last item. As we all know, global video game industry is having a hard time trying to make a quantum leap to next-gen video games, as well as keeping the cash flow pumping. Let’s face it, upgrading a business model while doing business is risky! You need to educate developers, reorganize teamwork and improve asset management, while keeping an eye on the ongoing projects and meeting the deadlines. A kind of “make something new, and keep the business running old-fashioned way” situation.

“…using both current and upcoming tools/assets.”

This is exactly where my upgraded workflow comes handy. In simple terms, it is a next-gen game development workflow offering an optimized way of making games for less money/time, using both current and upcoming tools/assets. Because it is backwards compatible, a veteran game development team/company can still use their old-fashioned workflow and make a smooth transition to next-gen video game development process using this workflow.

So far so good, but…

Why on earth is that backward compatibility thing so important? Simply because, when we say “workflow assets”, we are actually speaking about human beings! People with families, children, and responsibilities.

During the last 30 years, I have witnessed the highs and lows of the game development industry. It has always been very harsh on developers on critical occasions. When a “next-big thing” is in, managers start headhunting for next-gen guys. Current developers instantly turn into “old-fashioned guys”, and most of the time get fired. The turnover is so high that most experienced video game developers hate working inhouse for AAA companies. Instead, they prefer freelance business, just like me.

Frankly speaking, I upgraded my workflow to version 3 for a better human resource management. The first 2 versions favoured the management and income aspects of business. Now, the final version concentrates on developers. – Yep, something for my teammates!

We don’t work in a vacuum

Our environment feeds into the work we produce, particularly when that work is creative. Every piece of “thing” in our working environment affects us. What we see, listen, touch, and even smell, stimulates our creativity and in a way gets injected to our piece of work.

My humble home office

So, I made a radical decision. In order to increase my productivity, I decided to split my home office activities into two. Thanks to a painstaking and backaching performance, I moved all my coding/artwork related books, tools and computers from my mom’s house to home. Using some modular equipment from Ikea, I built a custom table wide enough for my desktop monitor and Wacom tablet, and spent a lot of time for cabling and ergonomics. Keeping things tidy, certainly served well. As I promised my beloved wife that I will use less than 2 m² of our living room, I have finally managed to create a wide open space using only 1.98 m². – Oh, that is optimization 😉

Within just a few days, I have realized a positive impact in my productivity. Now, my process is crystal clear. I do all my coding/artwork at home, and music related stuff in mom’s house. And the bonus is, I spend less time in traffic and more with my family.

“Creativity is a gift. It doesn’t come through if the air is cluttered.” – (John Lennon)

More details

Actually, I have so many things to tell you. I really would like to tell more and give you under the hood –technical- details of my upcoming project… I am afraid, I can’t. Until the official announcement, there are things not meant to be known or seen by public. Well, you know, this is how video game business works!

So, I’ll keep you posted whenever I can…

Tonight

Regarding the latest annual update and current status of my new video game project, I’m planning to open a bottle of wine and enjoy rest of the evening with my family. I think I deserved it.

See you next year!

So you want to be a video game developer, huh?

No problem.

Read this, then we’ll talk about it 😉

Myths & Facts

Many people believe that video game developers earn millions, live in Hawaii, drive a Ferrari, and date Victoria’s Secret supermodels. Well, maybe some of my colleagues do… Not me, for sure.

“Hey, where are the supermodels ?!”

Contrary to popular belief, career in video game development is full of challenges. Besides dealing with coding hurdles and release date stress, where time is your enemy in both cases, you need to handle egocentric teamwork meetings while keeping an eye on the tight budget. If that is not enough, you need to refine your skills forever and ever to make sure that you are keeping up with the latest technological achievements, even before they are released. – “Hey, where are the supermodels?!”

Despite all challenges, a game developer’s life is actually more upbeat than speculated. Forget about all the challenges for a minute; the best part is the necessity of refining skills. When you keep on sharpening your technical/artistic skills, you’ll have a chance of tweaking industry standard workflows. With every tweak, you’ll add a bit of haute couture touch both to the project you’re working on, and to your signature development methods. The more you sculpt a unique style, the more you stand out from the rest. And, that makes a real difference, by all means.

Education necessary?

Most preferably yes, but not essential. I studied both Science and Arts, but have always considered myself an autodidact a self-taught person. Nobody taught me how to develop video games! Through rewarding self-discipline skills, studying various topics in Mathematics, Physics, Architecture, Sculpture and Philosophy helped me to increase self-knowledge and unleash my creative potential. I’m an advocate of the mantra, “never stop learning.”

Regarding the opportunity for learning new tricks, a new video game project still makes my heart beat like a butterfly, even after 30+ years of active coding. – I keep the spirit alive!

“Self-education is, I firmly believe, the only kind of education there is.” – (Isaac Asimov)

Manners Maketh Man

Video game development is challenging, sore and tough. Doing video game business is worse!

Because of cheap and dirty business tricks that you are not familiar with yet, your heart can be easily broken. You may lose self confidence by getting discouraged, no matter how talented you are. Misery plagues creativity! When days turn into nights, melancholy takes over. Then, your talent starts to fade away. At the final phase, you start asking yourself “What have I done to deserve this?”, and the more you question your manners the more you lose self confidence. A perfect vicious circle! – Yep, I’ve been there. I know what I’m talking about.

No worries! It’s not your fault.

Unlike typical businessmen -underestimating your skills in a hot meeting, while puffing the fume of an expensive cigar right into your eyes- game developers are artists. I’m afraid, raw capitalist tricks work on us, simply because we are fragile.

Here is the cure – Act by the book! Follow the unwritten rules & guidelines of professionalism, and be happy 😉

Develop a thick skin.

Be prepared for the worst.

Settle with “less”. – Less is more.

In case of failure; get angry, not sad. Stand up and fight!

In case of criticism; embrace it. It is a chance for sharpening your skills.

Be good at what you are doing, not the best! Best kills creativity, and feeds pride.

You better be really good at what you are doing!

For starters, spend some time with experienced game developers. Speak less, listen more, show respect, and be gentle. Pay attention to how they tolerate mistakes. It is mistakes, that makes an artist a better one. Good artists are well aware of it, most probably you are not. That makes a difference!

“Creativity is allowing yourself to make mistakes. Art is knowing which ones to keep.” – (Scott Adams)

Knighthood served as a “Free Man”

I have always been a freelancer; a “free man” with no chains tied to a game development company/publisher. I had the chance of picking the projects I wanted, working with people I liked, and always preferred creativity over materialism – Free as a bird!

Sounds too good?

Actually, it is a state of nirvana, that comes with a few costs!

Expect to work harder than full-time developers – You are a marathon runner, not a nine-to-fiver. Be prepared to work more than 10 hours a day.

“There is no substitute for hard work.” – (Thomas A. Edison)

Invest in yourself – Besides work, make some time for reading something “new”. Never underestimate the advantage of using latest technologies. Keep sharpening your skills regularly, and be ahead of full-timers.

“Give me six hours to chop down a tree and I will spend the first four sharpening the axe.” – (Abraham Lincoln)

Expect no respect from full-time developers – They are going to hate you! Simply because, you have already become what they want to be. – You have achieved the goals of becoming a “free” game developer. You are no more afraid of taking risks. You have right to say “No!”. Your talent is appreciated. And, you are well paid… Enough number of reasons to attract hatred. So, be a professional by getting prepared for a bunch of miserable/jealous full-timers gathered around a meeting table. Do not let the meeting room turn into a battlefield. Take control of the conversation by tolerance. Make sure they understand that you could have simply become one of them, if you hadn’t taken the risks!

“Go up close to your friend, but do not go over to him! We should also respect the enemy in our friend.” – (Friedrich Nietzsche)

Expect no credits – None at all. If you are well paid and your work is appreciated, this is all you’ll get for a long time. Within years, you’ll start getting credits for your work, for sure. However, you better accept the bitter truth that you’ll never get the same “fame factor” that full-timers do. Full-time dedication to a single developer/publisher is always rewarded with full credits. I am afraid, this is how it works… As a result of your anonymous contributions; you will not be famous, you will not be invited to release parties, and you will be purposely excluded from development team photos. Most embarrassingly, your existence will be denied while your work will always be remembered! – It’s easy to deal with this case; don’t confuse fame with success. For me, success is happiness.

“Fame is the thirst of youth.” – (Lord Byron)

Expect no money – At least for now! You’ll make plenty of money, soon, but this shouldn’t be the ultimate motivation of your career. Game development is all about “passion”. A passion for coding challenges, artwork challenges, teamwork challenges, and even more challenges that you do not expect at all. Keep in mind that you are solving technical problems for the sake of art. It is 100% fun! – In return, you’ll get paid for it, sooner or later.

“A wise man should have money in his head, but not in his heart.” – (Jonathan Swift)

Despite all psychological threats above, working in video game industry as a freelancer is the best way to serve and survive. Swimming with sharks in a pool will keep you prepared for anything. Contrary to full-time workers, take advantage of your freelance position; free your mind, be creative & productive, and dominate the pool. – In case you need Plan B, enjoy the luxury of switching to an another pool 😉

Beyond Barriers

Many people assume that living in Istanbul (Turkey) as a freelance game developer and doing business with international game developers/publishers would be the hardest thing to do. I hear, “But, you’ve got to be there!” kind of buzz all the time. – Actually, not at all. In addition to overcoming cultural complexities, living in Istanbul as a freelancer and doing business with international game developers/publishers has always been the smoothest part in my workflow.

Even back in 1984, it was a no-brainer process. Before our local post office had a fax machine for hire, I used to contact people by writing business letters and sending them my codes/artwork on cassette tapes. Yes, it used to take 2 months to get a reply from UK, but that was the way how business was done in those days! – Worth waiting every minute for, actually. Each and every day I used to ask mom if the postman had delivered something for me; an acceptance letter, a cassette tape with my next project specifications on it, a new release with my code/artwork in it, or a paycheck preferably.

When I started working in UK, things changed entirely. Peaceful days were gone. Never-ending meetings, heavy ego traffic, more chat, less work, and unsuccessful management tricks adding insult to injury by causing more stress as we get close to the release day! Yep, usual game development company stuff, same even today 😉

Take my word for it! Get rid of unnecessary distractors. If you are self-disciplined and well-organized, nothing compares to working at home as a freelancer. Today, we have e-mail, video conference and more than anything we need at our fingertips. Easier and faster than ever. Never mind the distance, focus on the business! Sharpen your skills. If you are really talented at something, there is simply no barrier for doing business globally.

The barriers are not erected which can say to aspiring talents and industry, “Thus far and no farther.” – (Ludwig van Beethoven)

One final word, young man… Keep in touch!

A lot of things have changed and evolved during the last 3 decades of game development, except one thing; the necessity of keeping in touch with your contacts! If you’re in entertainment business, keeping your relations alive is everything. – Sounds easy, but is actually hard to do.

3-bit Node Graph Architecture for Next-Gen Game Development

Speaking of my latest video game development project, yet an another milestone achieved. – Quite a tough one, indeed!

But first, please allow me to focus on some of the very basic mathematical logic definitions heavily used in software engineering, so that we can clearly understand what’s going on under the hood of a decent game development process.

Don’t worry, it’s not rocket science 😉

Some theory

All video games have gameplay mechanics based on logic. A game is “a set of story driven goals to achieve” from a programmer’s perspective.

When you open a chest, solve a puzzle or kill an enemy, you are actually triggering a logic unit that is predefined within the game code. Depending on game’s technical requirements and gameplay complexity, there can be thousands of these units forming a web of logic units.

Game programmers tend to use graph theory for defining and coding logic units. Each unit is symbolized with a simple geometric shape. A box, a circle, anything… And these units are connected to each other with links.

  “Logic units” (nodes) represent tasks that the player will perform.

  “Links” (lines) represent the relationship between the logic units.

Behaviour Analysis

A node graph architecture is almost identical to an electronic circuit. When you start executing a node graph code, you are actually branching from one component (node, in our case) to an another by the rules you’ve set for the logic units, just like electric current flowing from a resistor to a capacitor. And, as you can guess, this type of signal flow is 100% linear.

When the player accomplishes a task, the node related to that event will be “expired”. In other words, it will be dead. Expired nodes cannot be resurrected. Once they’re done, they will be ignored (skipped) during code execution, forever. – Which is unlikely in electronics! An electronic component, such as a resistor, a diode, etc. cannot be conditionally turned on/off.

Back to 2002 for a “classic” implementation: Flagger

During the “Culpa Innata” development sessions, we precisely knew that we needed a node graph architecture for handling game’s complex execution flow. Many discussions were held on the method of implementation. All members of the core management & development team were expert electric/electronics engineers with no experience in video game production [Reference], but me! As a video game programmer, my perspective towards node graph theory was naturally very different, contrary to their classical approaches. I wasn’t thinking in terms of voltage, current, etc., but focused on just one thing: optimized code execution.

Thanks to my Zilog Z80 and Motorola 68000 assembly language programming background, I offered the term “Flag” for the base logic unit (node), and teamed up with Mr. Mete Balcı for 3 weeks. In December 2002, we developed a tool called “Flagger”.

Pros and Cons

Flagger was a C++ code generator with a very handy visual interface similar to UE4’s current Blueprint approach. Using Flagger, we were able to add nodes, connect them to each other, program the logic behind the nodes/links, and even take printout of the whole node graph scenario. When the visual logic design process was over, it was just a matter of selecting “Generate C++ code” from the menu, and source code was generated within minutes.

Over the following years, Flagger evolved into a more sophisticated development tool capable of handling various scenarios. Although it was a very handy tool and saved many hours during “Culpa Innata” sessions, there were a few problems with the classical node graph theory that the implementation was based on;

  Flags were single threaded. Only one node was allowed to execute at a time. No multi-threading.

  Flags were expirable. When a task was done, related flag (node) was marked as “expired”, not deleted for the sake of logic integrity.

  Flags were not reusable. Once they were expired, there was no way of resurrecting them. – Inefficient memory usage, thanks to hundreds of expired nodes.

  Flags were heavily loaded with variables. Too many dialogue related “customized” variables were defined for special cases (exceptions). – Inefficient memory usage, once again.

  Flag execution flow wasn’t well optimized because of node-tree search algorithm. The more nodes we had, the longer it took to accomplish the search.

  Flag execution was linear. When a node was expired, the graph code was first searching for related nodes and then retriggering the whole diagram from the beginning, like an electronic circuit simulator. – Well, that was ideal for modeling a circuit, not for developing a video game!

A Modern Approach: 3-bit Worker!

13 years later, I have once again found an opportunity to dive into node graph theory, and just completed implementing a new architecture for my latest video game development project. Unlike Flagger, it is something extraordinary! It is very… atypical, unconventional, unorthodox… Well, whatever… You got it 😉

First of all, it has nothing to do with classical electric/electronic circuit theory. This time, I’m on my own, and approaching the problem as a software engineer. Everything I designed/coded is based on game requirement specifications. In other words, it is implemented with “practical usage” in mind.

  I have defined the basic logic unit (node), as a “worker”.(Due to functional similarities, I simply borrowed this term from Web Workers.)

  A worker is a background task with adjustable priority settings. It performs/responds like a hardware interrupt.

  Each worker is multi-threaded.

  Depending on conditional requirements, a worker can expire and/or live forever. If expired, it can be resurrected and/or reinitialized, while preserving its previous state. So, a worker is a 100% reusable node.

  Each worker uses only 3-bits! No additional variables, no references, nothing else. – (If necessary, a worker offers flexible architecture for additional variables. However, I find it totally unnecessary. 3-bits are more than enough!)

  Workers are object oriented. They can easily be inherited.

  Inherited workers don’t need additional logic variables. All child workers share the same 3-bit information that they inherited from their parents!

  Each worker has a time dependent linear workflow. Just like a reel-to-reel tape recorder, it can be played, paused, slowed down, accelerated, fast forwarded, rewinded, and stopped.

  Workers can be non-linearly linked to other Workers! Which means, node-tree search algorithms are no more necessary. There is no “main loop” for executing nodes! Code execution is pre-cached for optimum performance.

  Workers are optimized for event driven methodology. No matter how many concurrent active workers (threads) you have in the scene, there is practically no CPU overhead. Ideal for mobile scenarios.

  Workers are managed by “Managers”. A Manager is inherited from base Worker node. So, any worker can be assigned as a Manager.

  Workers can communicate with each other and access shared variables via Managers.

  Whole architecture is 100% platform independent. For a showcase, I’ve implemented it for Unreal Engine 4 using C++ and Blueprints. It can easily be ported to other game engines; such as Unity, CryEngine, etc.

  And, most important of all, everything is meticulously tested. – It’s working as of today 🙂

Any drawbacks?

Sure… Due to complexity of comprehending “a set of non-linearly linked time dependent linear nodes”, debugging can be a nightmare. As always, designing simplified and organized logic sets reduces potential problems. – I keep my logic sets neat and tidy 😉

So, what’s next?

Well, to be honest, since all theoretical stuff is done, I’ll switch to game content development. I am quite sure that I’ll keep on adding/removing things to my 3-bit node graph architecture. I will keep on improving it while preserving its simplicity, for sure.

“It is vain to do with more what can be done with less.” – (William of Ockham)

New Video Game Project: Annual Information Update 2014

The new video game project that I started working on a year ago, precisely, is going great! With respect to maintaining confidentiality, I still can’t share specific details with you, but I am more than happy to say that everything is going on “as planned”. – Something quite contrary to the nature of game development in general 😉

One for all, all for one

As the co-producer of the project, I have many responsibilities in addition to the usual things that I have to do. Game design, story development, programming, conceptual artwork design, 3d modeling, texturing, music production, etc. Although sounds like a one-man-army project, actually it is not.

“Only one artist takes all the responsibility…”

In order to preserve game’s artistic style, it is quite normal that only one artist takes all the responsibility of designing & planning everything, and making sure that things will be kept/done in that way. And, this is exactly what I am doing nowadays. – (At one point, we will have developers and artists contributing to the project, naturally. Until that moment, everything must be “well-defined”.)

Coding

Instead of creating detailed game design documents, some game development projects begin with “conceptual coding”. Same goes for this project. Contrary to traditional game development workflow that begins with documenting the game design, I decided to start with implementing a proof of concept.

Similar to LEGO building bricks, I have been coding fundamental elements of “gameplay”. As a result of these coding sessions, I have clearly envisioned a number of next-gen features that can possibly enrich our game.

We are currently evaluating the options. When the gameplay implementation is over, I’ll go back to game design document for sure. – (Yes, I know that it sounds a bit unorthodox, but I have my reasons. Sometimes it’s good to break old habits for the sake of creativity. In this game, I will let “gameplay” define and drive the game design!)

Spinners and Probability

Coding is all about making decisions. Getting your hands dirty in Mathematics has always been rewarding. Going back and forth between Calculus and Geometry is more than a stellar experience.  Not because it makes you a better programmer, but simply because it turns you into a “wise decision maker”.

In terms of design and implementation, this game development project is full of complex decisions. Thankfully, “coding” is the glue between questions and answers. When used wisely, coding offers new ways of dealing with decisions that you derive from Mathematics, and this is exactly what I’m trying to achieve throughout this project.

Content is King!

I spent a lot of time creating a narrative hook, which I believe is the most underestimated element in today’s game design trends! With references from 16-bit retro gaming era, I am quite sure that a well-defined hook creates a huge impact on gameplay.

“Admittedly, I had to make 7 revisions for a ‘great’ hook…”

It was a tough job. In order to fine-tune the hook, I had to rewrite it again and again for many times. After each rewrite, I left it on my bookshelf at least for a few weeks, so that I can completely concentrate on other things as well.  When I picked it up weeks later, I was objective enough to assess the tension and come up with fresh ideas. Each iteration added more flavour to the previous version. Admittedly, I had to make 7 revisions for a great hook, which later turned out to be “Level One”. – Worth every minute spent!

Hidden Treasure: “Workflow 2.0”

The most distinguishing element of this project is the optimized workflow that I have been working on as a side project for many years. Thanks to this workflow, our project will have the luxury of really dramatic cost savings, a more “talent oriented” development process, and the competence of keeping game design/style integrity throughout the development process.

So far, so good…

Still thousands of things to do, so I’m going back to work now.

I’ll keep you posted.

An unexpected surprise made my day!

Since the day I noticed his Star Wars, Alien and Predator sketches, I have always admired Tuncay Talayman’s artwork.

It has been a privilege –and a lot of fun– working with him during Culpa Innata development sessions (2001-2003). Even after all those years, his continuous passion for improving his techniques and seeking new ways of artistic expressions, still surprises me. The portrait below is one of them 😉

What a lovely surprise… Thank you very much Tuncay!

Tuncay Talayman's portrait of Mert Börü