【Game Engine Architecture 1】
1、This book is really just the beginning of a fascinating and potentially lifelong journey.
We’ll focus primarily on the engine itself, including a host of low-level foundation systems, the rendering engine, the collision system, the physics simulation, character animation, audio, and an in-depth discussion of what I call the gameplay foundation layer.
This layer includes the game’s object model, world editor, event system and scripting system. We’ll also touch on some aspects of gameplay programming, including player mechanics, cameras and AI.
2、This book is intended to be used as a course text for a two- or three-course college-level series in intermediate game programming.
Industrial-strength 3D game engines are still written primarily in C++.
3、A general-purpose job system can be used to unlock the power of concurrency within a game engine
3.1、常用的引擎：
1）Epic Games’ Unreal Engine 4
2）Valve’s Source engine
3）Crytek’s CRYENGINE® 3,
4）Electronic Arts DICE’s Frostbite™ engine
5）the Unity game engine
4、The role of producer is defined differently by different studios.
In some game companies, the producer’s job is to manage the schedule and serve as a human resources manager.
In other companies, producers serve in a senior game design capacity. Still other studios ask their producers to serve as liaisons between the development team and the business unit of the company (finance, legal, marketing, etc.). Some smaller studios don’t have producers at all. For example, at Naughty Dog, literally everyone in the company, including the two co-presidents, plays a direct role in constructing the game; team management and business duties are shared between the senior members of the studio.
5、A physics simulation may need to be updated 120 times per second in order to remain stable.
6、A rendering engine that was designed to handle intimate indoor environments probably won’t be very good at rendering vast outdoor environments. The indoor engine might use a binary space partitioning (BSP) tree or portal system to ensure that no geometry is drawn that is being occluded by walls or objects that are closer to the camera.
The outdoor engine, on the other hand, might use a less-exact occlusion mechanism, or none at all, but it probably makes aggressive use of level-of-detail (LOD) techniques to ensure that distant objects are rendered with a minimum number of triangles, while using high-resolution triangle meshes for geometry that is close to the camera.
7、MR（Mixed Reality），中文名称混合现实。MR是对VR和AR的进一步发展，以增强用户体验的真实感。
而MR和AR的区别在于：在MR的世界里，呈现在真实世界里的虚拟物体，并不会因为玩家位置改变而发生位移，它们的位置其实是相对固定的。在高级的MR世界里，用户很有可能分不清哪一个是虚拟物体，哪一个是现实物体。
8、Studies have shown that VR running at below 90 frames per second is likely to induce disorientation, nausea, and other negative user effects. This means that not only do VR systems need to render the scene twice per frame, they need to do so at 90+ FPS. This is why VR games and applications are generally required to run on highpowered CPU and GPU hardware.
9、Runtime Game Entine Architecture
1）底层。
2）中底层。
3）渲染层。
4）游戏层。
10、Collision & Physics
• Havok is a popular industrial-strength physics and collision engine.
• PhysX is another popular industrial-strength physics and collision engine, available for free download from NVIDIA.
• Open Dynamics Engine (ODE) is a well-known open source physics/collision package.
11、HUD：heads up display。指的是player头顶的UI。
GUI：graphical user interface。指的是游戏面板UI，如背包、菜单等等。
12、Full-Motion video (FMV) system in this layer. This system is responsible for playing full-screen movies that have been recorded earlier (either rendered with the game’s rendering engine or using another rendering package).
In-game cinematics (IGC) system. This component typically allows cinematic sequences to be choreographed within the game itself, in full 3D. For example, as the player walks through a city, a conversation between two key characters might be implemented as an in-game cinematic. IGCs may or may not include the player character(s). They may be done as a deliberate cut-away during which the player has no control, or they may be subtly integrated into the game without the human player even realizing that an IGC is taking place. Some games, such as Naughty Dog’s Uncharted 4: A Thief’s End, have moved away from pre-rendered movies entirely, and display all cinematic moments in the game as real-time IGCs.
13、Digital Content Creation.
14、Asset Conditioning Pipeline
ACP，将DCC导出的资源，处理成适用于 Engine引用的资源。
14.1、Brush Geometry
Brush geometry is defined as a collection of convex hulls, each of which is defined by multiple planes. Brushes are typically created and edited directly in the game world editor. This is essentially an “old school” approach to creating renderable geometry
15、Skeletal Animation Data
A skeletal mesh is a special kind of mesh that is bound to a skeletal hierarchy for the purposes of articulated animation. Such a mesh is sometimes called a skin.
An unoptimized skeletal animation is defined by a stream of 4 x 3 matrix samples, taken at a frequency of at least 30 frames per second, for each of the joints in a skeleton (of which there can be 500 or more for a realistic humanoid character). Thus, animation data is inherently memory-intensive. For this reason, animation data is almost always stored in a highly compressed format. Compression schemes vary from engine to engine, and some are proprietary. There is no one standardized format for game-ready animation data.
16、 Perforce
Perforce is a professional-grade source control system, with both text-based and GUI interfaces. One of Perforce’s claims to fame is its concept of change lists. A change list is a collection of source files that have been modified as a logical unit. Change lists are checked into the repository atomically—either the entire change list is submitted, or none of it is.
Perforce is used by many game companies, including Naughty Dog and Electronic Arts.
17、Libraries, Executables and Dynamic Link Libraries
When a translation unit is compiled, the resulting machine code is placed in an object file (files with a .obj extension under Windows or .o under UNIX-based operating systems). The machine code in an object file is:
• relocatable, meaning that the memory addresses at which the code resides have not yet been determined
• unlinked, meaning that any external references to functions and global data that are defined outside the translation unit have not yet been resolved.
Object files can be collected into groups called libraries. A library is simply an archive, much like a ZIP or tar file, containing zero or more object files. Libraries exist merely as a convenience, permitting a large number of object files to be collected into a single easy-to-use file.
17.1、_DEBUG & NDEBUG
As a ubiquitous example, the symbol _DEBUG is always defined for a debug build, while in non-debug builds, the symbol NDEBUG is defined instead.
18、Local and Global Optimizations
Local optimizations operate only on small chunks of code known as basic blocks. Roughly speaking, a basic block is a sequence of assembly language instructions that doesn’t involve a branch. Local optimizations include things like:
• algebraic simplification,
• operator strength reduction (e.g., converting x / 2 into x >> 1 because the shift operator is “lower strength” and therefore less expensive than the integer division operator),
• code inlining,
• constant folding (recognizing expressions that are constant at compile time and replacing such expressions with their known value),
• constant propagation (replacing all instances of a variable whose value turns out to be constant with the literal constant itself),
• loop unrolling (e.g., converting a loop that always iterates exactly four times with four copies of the code within the loop, in order to eliminate conditional branching),
• dead code elimination (removal of code that has no effect, such as removing the assignment expression x = 5; if it is immediately followed by another assignment to x like x = y + 1;), and
• instruction reordering (in order to minimize CPU pipeline stalls).
link-time optimizations (LTO).
optimize its most performance-critical code paths.
18.1、Typical Build Configurations
1）debug：关闭优化，开启Debug模块
2）development：开启优化，开启Debug功能。
3）ship：开启优化，关闭Debug功能。
19、Visual Studio Linker Property Page
of the final product of the build, usually an executable or DLL.
link into the final executable.
application..
Note that Visual Studio employs various “magic spells” to specify libraries that should be linked into an executable. For example, a special #pragma instruction in your source code can be used to instruct the linker to automatically link with a particular library. For this reason, you may not see all of the libraries you’re actually linking to in the “Additional Dependencies” field. (In fact, that’s why they are called additional dependencies.) You may have noticed, for example, that Direct X applications do not list all of the DirectX libraries manually in their “Additional Dependencies” field. Now you know why.
20、 suffix of watcher window
• The “,d” suffix forces values to be displayed in decimal notation.
• The “,x” suffix forces values to be displayed in hexadecimal notation.
array data that is referenced through a pointer.
this:
my_array,[my_array_count]
named my_array.
21、数据断点
a hardware breakpoints.
21.1、Memory Leak and Corruption Detection
can’t hurt. Thankfully, many such tools exist.
problem is linked directly to the source code that caused the problem, make ing tracking down and fixing these kinds of problems relatively easy.
22、Multiple Inheritance
mix-in classes.
大多数 C++ 开发者禁用多重继承。主流的做法是，只有单一继承链上的类可以多重继承，但只能继承无父类的非本链类型，从而保证不会出现死亡钻石。这样的类叫 mix-in classes。
23、Composition and Aggregation
and tend to underutilize aggregation and composition.
24、C++11 Auto
As such, we decided to adopt a simple rule:
auto may only be used when declaring iterators, in situations where no other approach works (such as within template definitions), or in special cases when code clarity, readability and maintainability is significantly improved by its use. In all other cases, we require the use of explicit type declarations.
顽皮狗限制使用 auto.
25、template metaprogramming.
costs.
26、user error & programmer error
code itself.
working—or in the case of a game, to continue playing.
be caught and fixed before the software ships to the public.
27、Exception Handling
by the stack unwinding process.
functions might be above you on the call stack when you throw an exception.
项目的任意一个文件，如果启用了 try catch，或 throw，则整个项目所有的函数都会被扩展，以添加 exception unwind 信息。从而导致性能下降。
That said, it is possible to “sandbox” a library or libraries that make use of exception handling, in order to avoid your entire game engine having to be written with exceptions enabled. To do this, you would wrap all the API calls into the libraries in question in functions that are implemented in a translation unit that has exception handling enabled. Each of these functions would catch all possible exceptions in a try/catch block and convert them into error return codes. Any code that links with your wrapper library can therefore safely disable exception handling.
要想避免，可以将带 try-catch、throw 的代码，封装到一个库里面。
Clearly there are some pretty strong arguments for turning off exception handling in your game engine altogether. This is the approach employed at Naughty Dog and also on most of the projects I’ve worked on at Electronic Arts and Midway.
28、assert
defined).
29、static_assert
C++11中引入。
30、顽皮狗工作室用lisp方言作为游戏配置脚本。
31、Fixed-Point
32、Floating-Point
m is the fractional value stored in the mantissa.
and vice versa.
The largest possible floating-point value, FLT_MAX = 3.403 x 10^38.
• An exponent of 255 has a special meaning in the IEEE-754 format—it is used for values like not-a-number (NaN) and infinity —so it cannot be used for regular numbers. Hence the maximum eight-bit exponent is actually 254, which translates into 127 after subtracting the implicit bias of 127.
33、Subnormal Values
is ：
and +FLT_MIN.
zero is represented by the constant FLT_TRUE_MIN.
exponent值为0的数，即为 subnormal value. 在计算时，将mantissa隐含的前置1给去除。subnormal value 将 -FLT_MIN、FLT_MIN之间的值均分。最接近0的值为 FLT_TRUE_MIN。
如果不使用subnormal，当 a!=b时， a-b==0 也有可能成立。
34、Machine Epsilon
the machine epsilon is defined to be the smallest floating-point value # that satisfies the equation, 1+ Epsilon != 1. For an IEEE-754 floating-point number, with its 23 bits of precision, the value of Epsilon is 2^(-23), which is approximately 1.192x10^(-7). The most significant digit of Epsilon falls just inside the range of significant digits in the value 1.0, so adding any value smaller than # to 1.0 has no effect. In other words, any new bits contributed adding a value smaller than # will get “chopped off” when we try to fit the sum into a mantissa with only 23 bits.
35、Units in the Last Place（ULP）
ULP指的是 mantissa的最后一位的大小。当浮点数值为1时，1ULP大小为 2^(-23)。当浮点数值为2时，1ULP增大2倍（因为整体 mantissa左移了一位），大小为2^(-22)。
The concept of units in the last place illustrates the idea that the precision of a floating-point number depends on its exponent.
It can also be useful for finding the floating-point value that is the next largest representable value relative to a known value, or conversely the next smallest representable value relative to that value.
36、Before C++11, programmers had to rely on non-portable sized types provided by their compiler.
For example, the Visual Studio C/C++ compiler defined the following extended keywords for declaring variables that are an explicit number of bits wide: __int8, __int16, __int32 and __int64.
Most other compilers have their own “sized” data types, with similar semantics but slightly different syntax.
at Naughty Dog we use the following sized types:
• F32 is a 32-bit IEEE-754 floating-point value.
16-, 32- and 64-bit integers, respectively.
CPU.
<cstdint>
I32F and U32F types we defined at Naughty Dog).
37、OGRE’s Primitive Data Types
Ogre::Real 默认是 float，如果 _PRECISION 为1，则Ogre::Real 会成为 double。
38、LIttle-endian & Big Endian
1）Little-endian. byte, we say that the processor is little-endian.
2）Big-endian. If a microprocessor stores the most significant byte of a multibyte value at a lower memory address.
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