3D游戏编程GPU编程基础.pdf

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1、GPU Programming Yanci Zhang Game Programming IIGame Programming II GPU overview OpenGL shading language overview Vertex/Geometry/Fragment shader Application:Per-pixel shading Game Programming IIGame Programming II Outline GPU:Graphics Processing Unit Developed rapidly from being primitive drawing de

2、vices to being major computing resources Extremely powerful and flexible processor Tremendous memory bandwidth and computational power High level languages have emerged Capable of general-purpose computation beyond graphics applications Game Programming IIGame Programming II What is GPU?In many resp

3、ects GPU is more powerful than CPU Computational power:FLOPS(Floating point Operations Per Second)Parallelism Bandwidth Performance growth rate Game Programming IIGame Programming II Motivation FLOPS:A common benchmark measurement for rating the speed of FPU CPU Intel Core i7 980 XE(quad-core):107.5

4、5 GFLOPS GPU nVidia GeForce GTX 480:2.02 TFLOPS Modern GPUs support high precision 32-bit floating point throughout the pipeline No support for a double precision format Game Programming IIGame Programming II Floating Point Calculation Parallelism:allows simultaneous operations at the same time CPU

5、Do not adequately exploit parallelism Dual-core,quad-core GPU GeForce GTX 480:512 kernels Game Programming IIGame Programming II Parallelism Peak performance of computer systems is often far in excess of actual application performance The bandwidth between key components ultimately dictates system p

6、erformance CPU 64bits DDR3-2133 dual-channel:17GB/s GPU GeForce GTX 480:384bits,177.4GB/s Game Programming IIGame Programming II Bandwidth CPU Annual growth 1.5x-decade growth 60 x Moores law GPU Annual growth 2.0 x-decade growth 1000 x Faster than Moores law Multi-billion dollar video game market i

7、s a pressure cooker that drives innovation Game Programming IIGame Programming II Getting Faster and Faster Efficient computation Maximize the hardware devoted to computation Allow parallelism Task parallelism Data parallelism Instruction parallelism Ensure each computation unit operates at maximum

8、efficiency Game Programming IIGame Programming II Keys to High-Perf.Computing Efficient communication Simply providing large amounts of computation is not sufficient PEs often spend most of the time waiting for data Minimize off-chip communication Game Programming IIGame Programming II Keys to High-

9、Perf.Computing A programming model allowing high efficiency in computation and communication Two basic components Stream All data is represented as a stream An ordered set of data of the same data type Kernels:operations on streams Applications are constructed by chaining multiple kernels together G

10、ame Programming IIGame Programming II Stream Programming Model Operates on entire streams of elements and produces new streams Within a kernel,computations on one stream element are never dependant on computations on another element Input elements and intermediate computed data are stored locally Fi

11、ts perfectly onto data-parallel hardware Game Programming IIGame Programming II Kernel Use of transistors can be divided to three categories:Control:direct the computation Datapath:perform computation Storage:store data Game Programming IIGame Programming II Efficient Computation(1)Only simple contr

12、ol flow in kernel execution Devote most of transistors to datapath hardware rather than control hardware Streams expose parallelism in the application Allows a hardware implementation to specialize hardware Game Programming IIGame Programming II Efficient Computation(2)Off-chip communication is effi

13、cient Intermediate results between kernels are kept on-chip to minimize off-chip communication High degree of latency tolerance Game Programming IIGame Programming II Efficient Communication Prescribes both the operation to be executed and the required data Only a limited prefetch of the input data

14、can occur Jumps are expected in the instruction stream L2 cache consumes lots of the transistors in CPU Game Programming IIGame Programming II Instruction-Stream-Based(CPU)Separates two tasks:Configuring PEs Controlling data-flow to and from PEs Data elements can be assembled from memory before proc

15、essing Uses only small caches and devotes the majority of transistors to computation Game Programming IIGame Programming II Data-Stream-Based(GPU)The stream formulation of the graphics pipeline All data as streams All computation as kernels Both user-programmable and nonprogrammable stages can be ex

16、pressed as kernels Game Programming IIGame Programming II Mapping Pipeline to Stream Model Fixed Very fast Can not modify the pipeline,only can turn on/off some functions Hard to implement advanced techniques on GPU Programmable Allows programmers to write shaders to change the pipeline Game Program

17、ming IIGame Programming II Fixed vs.Programmable Three programmable kernels in pipeline Vertex shader Geometry shader Pixel shader Load shaders through graphics API The fixed pipeline are replaced by shaders Game Programming IIGame Programming II Programmable Graphics Hardware MIMD:Multiple Instruct

18、ion stream,Multiple Data stream A number of processors that function asynchronously and independently Game Programming IIGame Programming II Vertex Processor Operate on a single input vertex and produce a single output vertex Replace transformation&lighting unit Now you have to do everything by your

19、self Transformation Lighting Texture coordinates generation As a minimum,a vertex shader must output vertex position in homogeneous clip space Game Programming IIGame Programming II Vertex Shader:Basic Function What else we can do?Displacement mapping Object deformation Vertex blending Game Programm

20、ing IIGame Programming II Vertex Shader:Advanced Function We can not Add or delete any vertices Change the primitive type Change the order of vertices form the primitives No knowledge of the type of primitive and neighboring vertices Game Programming IIGame Programming II Vertex Shader:Limitations S

21、IMD:Single Instruction,Multiple Data Achieves data level parallelism “get this pixel,get the next one”-“get lots of pixel”Game Programming IIGame Programming II Fragment Processor Invoked once for each fragment covered by the primitive Computes the final pixel color and depth Can output up to 8 32-b

22、it 4-component data for the current pixel location Game Programming IIGame Programming II Fragment Shader:Basic Function Enables rich shading techniques Per-pixel lighting,bump mapping,normal mapping Fluid simulation Game Programming IIGame Programming II Fragment Shader:Advanced Function Dynamic br

23、anching less efficient than vertex proc.Can not change the screen coordinate of a fragment No arbitrary memory write Game Programming IIGame Programming II Fragment Shader:Limitations New for 2007 Executed after vertex shaders Input:whole primitive,possibly with adjacent information Invoked once for

24、 every primitive Output:multiple vertices forming a single selected topology(tristrip,linestrip,pointlist)Output may be fed to rasterizer and/or to a vertex buffer in memory Game Programming IIGame Programming II Geometry Shader Point Sprite Expansion Single Pass Render-to-Cubemap Dynamic Particle S

25、ystems Fur/Fin Generation Shadow Volume Generation Game Programming IIGame Programming II Geometry Shader:Applications Graphics applications Per-pixel lighting Ray tracing Deformation GPGPU Computer vision Physically-based simulation Image processing Database queries Game Programming IIGame Programm

26、ing II Programmable GPUs:Applications General-purpose Computation on GPUs Capable of performing more than the specific graphics computations Goal:make the inexpensive power of the GPU available to developers as a sort of computational coprocessor Example applications range from in-game physics simul

27、ation to conventional computational science Game Programming IIGame Programming II GPGPU Production rendering Geared towards maximum image quality Example:RenderMan Real-time rendering GLSL:OpenGL shading language HLSL:DirectX High-level shading language CG:C for Graphcis,nVidia Game Programming IIG

28、ame Programming II Shading Language High level shading language based on C Not a hardware-specific language Cross platform compatibility on multiple OS Each hardware vender includes GLSL compiler in their driver Game Programming IIGame Programming II OpenGL Shading Language Check whether your GPU su

29、pports GLSL GLSL is part of OpenGL 2.0 If OpenGL 2.0 is not available,then use OpenGL extensions Game Programming IIGame Programming II Before Using GLSL GL_ARB_shader_object Adds API calls that are necessary to manage shader objects and program objects GL_ARB_fragment_shader Adds functionality to d

30、efine fragment shader objects GL_ARB_vertex_shader Adds functionality to define vertex shader objects Game Programming IIGame Programming II Extensions Required GLEW:The OpenGL Extension Wrangler Library(http:/ GLEW Game Programming IIGame Programming II GLEW 1/2#include#include .glutInit(&argc,argv

31、);glutCreateWindow(GLEW Test);GLenum err=glewInit();if(GLEW_OK!=err)/*Problem:glewInit failed,something is seriously wrong.*/fprintf(stderr,Error:%sn,glewGetErrorString(err);.Check extensions Check core OpenGL functionality Game Programming IIGame Programming II GLEW 2/2 if(GLEW_ARB_vertex_shader)/*

32、It is safe to use the GL_ARB_vertex_shader extension here.*/if(GLEW_VERSION_2_0)/*Yay!OpenGL 2.0 is supported!*/Scalar bool,int,float Vector Supports 2D,3D,4D vector:vec2,3,4,ivec2,3,4,bvec2,3,4 Matrix Square matrix:mat2,mat3,mat4 mat2x3,mat2x4,mat3x2,mat3x4,mat4x2,mat4x3 Texture sampler1D,sampler2D

33、,sampler3D samplerCube sampler1DShadow,sampler2DShadow Game Programming IIGame Programming II Data Types Pretty much the same as in C Flexible when initializing variables using other variables Game Programming IIGame Programming II Variables 1/3 float a,b;/two float variables(the comments are like i

34、n C)int c=2;/initialize a variable when declaring it vec3 g=vec3(1.0,2.0,3.0);/declare and initialize a vector vec2 a=vec2(1.0,2.0);vec2 b=vec2(3.0,4.0);vec4 c=vec4(a,b)/c=vec4(1.0,2.0,3.0,4.0);Flexible when accessing a vector x,y,z,w:accessing vectors that represent points or normals r,g,b,a:access

35、ing vectors that represent colors s,t,p,q:accessing vectors that represent texture coordinates Game Programming IIGame Programming II Variables 2/3 Accessing components beyond those declared for the vector type is an error Game Programming IIGame Programming II Variables 3/3 vec4 a=vec4(1.0,2.0,3.0,

36、4.0);float posX=a.x;/posX=1.0 float posY=a1;/posY=2.0 float depth=a.w;/depth=4.0 Vec3 b=a.xxy;/b=vec3(1.0,1.0,2.0)Vec3 c=a.bra;/b=vec3(3.0,1.0,4.0)vec2 t=vec2(1.0,2.0);float tt=t.z;/incorrect!Operations are component-wise Game Programming IIGame Programming II Vector and Matrix Operations vec3 u,v,w

37、;float f;mat3 a1,a2,a3;u=v+f;u=v+w;u=v*a1;a1=a2*a3;u.x=v.x+f;u.y=v.y+f;u.z=v.z+f;u.x=v.x+w.x;u.y=v.y+w.y;u.z=v.z+w.z;u.x=dot(v,a10);u.y=dot(v,a11);u.z=dot(v,a12);selection(if-else)iteration(for,while,and do-while)jumps(discard,return,break,and continue)discard is only allowed within fragment shaders

38、 discard causes the fragment to be discarded and no updates to any buffers will occur Game Programming IIGame Programming II Control Flow Statements if(depth 0.5)discard;The function main()is used as the entry point to a shader executable Game Programming IIGame Programming II Function Definition re

39、turnType functionName(type0 arg0,type1 arg1,.,typen argn)/do some computation return returnValue;gl_Position(vec4)Output of vertex shader Homogeneous vertex position Must write a value into this variable gl_FragCoord(vec4)Holds the window relative coordinates x,y,z,and 1/w values for the fragment Re

40、ad-only variable in fragment shader Game Programming IIGame Programming II Important Build-in Variables 1/2 gl_FragColor (vec4)Output of fragment shader Writing to gl_FragColor specifies the fragment color gl_FragDepth(float)Output of fragment shader Default value:gl_FragCoord.z If you write to gl_F

41、ragDepth,then it is your responsibility for always writing it Game Programming IIGame Programming II Important Build-in Variables 2/2 Angle and trigonometry functions sin,cos,asin,acos Exponential functions pow,exp,sqrt Common functions abs,clamp,smoothstep Geometric functions length,dot,cross Game

42、Programming IIGame Programming II Build-in Functions Matrix functions outerProduct,transpose Vector relational functions lessThan,equal Texture lookup functions texture2D,texture2DLod Fragment processing functions Noise functions Game Programming IIGame Programming II Build-in Functions ftransform()

43、For vertex shaders only Produces exactly the same result as would be produced by OpenGLs fixed functionality transform reflect(vec3 I,vec3 N)Computes reflection vector by incident vector I and normal vector N Game Programming IIGame Programming II Important Build-in Functions gl_Position=ftransform(

44、)Vertex shader Fragment shader Game Programming IIGame Programming II First Example void main()gl_Position=ftransform();void main()gl_FragColor=vec4(1.0,1.0,1.0,1.0);Game Programming IIGame Programming II Make Fun of Fragment Shader void main()vec4 t=vec4(1.0,0.6,0.3,0.0);gl_FragColor=t.xxxx;/flexib

45、le vector accessing void main()gl_FragColor=vec4(gl_FragCoord.zzz,1.0);/lets view the depth map void main()if(gl_FragCoord.x 320)discard;/try discard gl_FragColor=vec4(1.0,1.0,1.0,1.0);Vertex shader build-in attributes gl_Vertex,gl_Normal,gl_Color,gl_MultiTexCoord Vertex shader build-in output varia

46、bles gl_FrontColor,gl_TexCoord Fragment shader build-in input variables gl_Color,gl_TexCoord Built-In uniform state gl_ModelViewMatrix,gl_ProjectionMatrix Game Programming IIGame Programming II More Build-in Variables Game Programming IIGame Programming II Example:Using Build-in Matrixes void main()

47、gl_Position=ftransform();void main()gl_Position=gl_ModelViewProjectionMatrix*gl_Vertex;void main()gl_Position=gl_ModelViewMatrix*gl_Vertex;gl_Position=gl_ProjectionMatrix*gl_Position;Vertex shader Fragment shader Game Programming IIGame Programming II Example:Using Colors void main()gl_Position=ftra

48、nsform();gl_FrontColor=gl_Color;void main()gl_FragColor=gl_Color;Vertex shader Fragment shader Game Programming IIGame Programming II Example:Using Texture Coordinates void main()gl_Position=ftransform();gl_TexCoord0=vec4(gl_MultiTexCoord0.xy,1.0,0.0);void main()gl_FragColor=gl_TexCoord0;Important t

49、o per-vertex and per-pixel lighting Transpose of the inverse of the upper leftmost 3x3 of gl_ModelViewMatrix Converts normal vector from object space to eye space Game Programming IIGame Programming II gl_NormalMatrix void main()gl_FragColor=gl_Color;Vertex shader Fragment shader Game Programming II

50、Game Programming II View Normal Vectors void main()gl_Position=ftransform();gl_FrontColor=vec4(gl_Normal,1.0);void main()gl_Position=ftransform();gl_FrontColor=vec4(gl_NormalMatrix*gl_Normal,1.0);Communication between OpenGL and shader One way communication Use uniform qualifier when declaring varia