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1 Introduction to the Hardware Graphics Pipeline Introduction To Overview of the Tutorial: Morning Tutorial 5: Programming Graphics Hardware 8:30 Introduction to the Hardware Graphics Pipeline Introduction to Cyril Zeller the Hardware Graphics Pipeline 9:30 Controlling the GPU from the CPU: the 3D API Cyril Zeller Cyril Zeller 10:15 Break 10:45 Programming the GPU: High-level Shading Languages Randy Fernando 12:00 Lunch Tutorial 5: Programming Graphics Hardware Overview of the Tutorial: Afternoon Overview Concepts: 12:00 Lunch Real-time rendering 14:00 Optimizing the Graphics Pipeline Hardware graphics pipeline Matthias Wloka Evolution of the PC hardware graphics pipeline: 14:45 Advanced Rendering Techniques 1995-1998: Texture mapping and z-buffer Matthias Wloka 1998: Multitexturing 15:45 Break 1999-2000: Transform and lighting 16:15 General-Purpose Computation Using Graphics Hardware 2001: Programmable vertex shader Mark Harris 2002-2003: Programmable pixel shader 2004: Shader model 3.0 and 64-bit color support 17:30 End PC graphics software architecture Performance numbers Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Real-Time Rendering Hardware Graphics Pipeline Graphics hardware enables real-time rendering Application Geometry Rasterization 3D Triangles 2D Triangles Pixels Real-time means display rate at more than 10 images per second Stage Stage Stage For each For each triangle: triangle vertex: Rasterize Transform triangle 3D position Interpolate into vertex attributes screen position across triangle Compute Shade attributes pixels 3D Scene = Image = Resolve visibility Collection of Array of pixels 3D primitives (triangles, lines, points) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 1 PC Architecture 1995-1998: Texture Mapping and Z-Buffer CPU GPU Motherboard Application / Geometry Stage Rasterization Stage Raster Texture Central Processor Unit (CPU) Rasterizer Operations Unit Unit System Memory Bus Port (PCI, AGP, PCIe) 2D Triangles Bus Frame 2D Triangles Textures Textures (PCI) Buffer Video Memory System Memory Video Memory Graphics Processor Unit (GPU) PCI: Peripheral Component Interconnect 3dfx’s Voodoo Video Board Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Texture Mapping Texture Mapping: Texture Coordinates Interpolation Triangle Meshtextured with Base Texture Screen Space Texture Space x u (x1, y1) + y v (u1, v1) (x, y) (x0, y0) (u, v) (x2, y2) (u0, v0) = (u2, v2) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Texture Mapping: Perspective-Correct Interpolation Texture Mapping: Magnification Screen Space Texture Space x u y v Perspective-Incorrect Perspective-Correct or Nearest-Point Sampling Bilinear Filtering Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 2 Texture Mapping: Minification Texture Mapping: Mipmapping Screen Space Texture Space x u y v or Bilinear Filtering Trilinear Filtering Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Texture Mapping: Anisotropic Filtering Texture Mapping: Addressing Modes or Wrap Mirror Bilinear Filtering Trilinear Filtering Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Texture Mapping: Addressing Modes Raster Operations Unit (ROP) Raster Operations stencil buffer value Unit at (x, y) tested against Texture Rasterizer Fragments Scissor Test reference value Unit Fragment Alpha Test tested against Frame Buffer Screen Position (x, y) scissor rectangle Stencil Test Stencil Buffer tested against Alpha Value a reference value Z Test Z-Buffer tested against Depth z z-buffer value at (x, y) Color Buffer (visibility test) Alpha Blending Pixels blended with color buffer value at (x, y): Clamp Border Color (r, g, b) Ksrc * Colorsrc + Kdst * Colorsrc (src = fragment dst = color buffer) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 3 1998: Multitexturing AGP CPU GPU PCI uses a parallel connection Application / Geometry Stage Rasterization Stage AGP uses a serial connection Raster Multitexture Rasterizer Operations → Less pins, simpler protocol → Cheaper, more scalable Unit Unit PCI uses a shared-bus protocol AGP uses a point-to-point protocol → Bandwidth is not shared among devices 2D Triangles Bus Frame 2D Triangles Textures Textures (AGP) Buffer AGP uses a dedicated system memory called AGP memory or non-local video memory System Memory Video Memory The GPU can lookup textures that resides in AGP memory AGP: Accelerated Graphics Port NVIDIA’s TNT, ATI’s Rage Bandwidth: AGP = 2 x PCI (AGP2x = 2 x AGP, etc.) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Multitexturing 1999-2000: Transform and Lighting Base Texturemodulated by Light Map CPU GPU “Fixed Function Pipeline” Application Geometry Stage Rasterization Stage Stage Raster Transform Register Rasterizer Operations and Combiner Unit Lighting X Unit Texture Unit 3D Triangles Textures Bus Frame from UT2004 (c) 3D Triangles Textures (AGP) Epic Games Inc. Buffer Used with permission System = Memory Video Memory Register Combiner: Offers many more texture/color combinations NVIDIA’s GeForce 256 and GeForce2, ATI’s Radeon 7500, S3’s Savage3D Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Transform and Lighting Unit (TnL) Bump Mapping Transform and Lighting Unit Bump mapping is about fetching the normal from a texture (called a normal map) instead of using the interpolated normal to compute Transform lighting at a given pixel World World View Perspective Model Camera Projection Screen Matrix Space Matrix Division or or Projection or or and Object Eye Matrix Clip Window Model-View Viewport Space Space Space Space Matrix Matrix Lighting Material Properties Vertex Light Properties Diffuse and Specular Color Normal Map Vertex Color Diffuse light without bump Diffuse light with bumps Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 4 Cube Texture Mapping Projective Texture Mapping Cubemap Projected Texture (covering Environment Mapping (x, y, z, w) the six faces z (x (the reflection vector of a cube) ,y,z y (x/w, y/w) Texture Projection ) is used to lookup x the cubemap) Cubemap lookup Projective Texture lookup (with direction (x, y, z)) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 2001: Programmable Vertex Shader Vertex Shader CPU GPU A programming processor for any per-vertex computation Application Geometry Stage Rasterization Stage void VertexShader( Stage Raster // Input per vertex Register in float4 positionInModelSpace, Vertex Shader Rasterizer Operations (no flow control) (with Z-Cull) Combiner in float2 textureCoordinates, Unit in float3 normal, Texture // Input per batch of triangles uniform float4x4 modelToProjection, Shader uniform float3 lightDirection, // Output per vertex out float4 positionInProjectionSpace, 3D Triangles out float2 textureCoordinatesOutput, out float3 color Textures Bus Frame ) 3D Triangles Textures { (AGP) Buffer // Vertex transformation System positionInProjectionSpace = mul(modelToProjection, positionInModelSpace); Memory Video Memory // Texture coordinates copy Z-Cull: Predicts which fragments will fail the Z test and discards them textureCoordinatesOutput = textureCoordinates; Texture Shader: Offers more texture addressing and operations // Vertex color computation color = dot(lightDirection, normal); NVIDIA’s GeForce3 and GeForce4 Ti, ATI’s Radeon 8500 } Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware Volume Texture Mapping Hardware Shadow Mapping Shadow Map Computation z/w The shadow map contains the depth z/w of the 3D points visible (x, y, z, w) from the light’s point of view: Spot (x/w, y/w) light Shadow Rendering shadow z map A 3D point (x, y, z, w) is in shadow if: value (x,y,z) y z/w < value of shadow map at (x/w, y/w) (x, y, z, w) x Spot Volume Texture Noise Perturbation A hardware shadow map lookup (x/w, y/w) light (3D Noise) returns the value of this comparison between 0 and 1 Volume Texture lookup (with position (x, y, z)) Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 5 Antialiasing: Definition Antialiasing: Supersampling and Multisampling Supersampling: Pixel Center Aliasing: Undesirable visual artifacts due to Compute color and Z at insufficient sampling of: higher resolution and Sample Primitives (triangles, lines, etc.) → jagged edges display averaged color to smooth out the visual Textures or shaders → pixelation, moiré patterns artifacts Those artifacts are even more noticeable on animated images. Multisampling: Antialiasing: Method to reduce aliasing Same thing except only Z Texture antialiasing is largely handled by proper is computed at higher mipmapping and anisotropic filtering resolution Multisampling performs Shader antialiasing can be tricky (especially with antialiasing on primitive conditionals) edges only Tutorial 5: Programming Graphics Hardware Tutorial 5: Programming Graphics Hardware 2002-2003: Programmable Pixel Shader Pixel Shader CPU GPU A programming processor for any per-pixel computation Application Geometry Stage Rasterization Stage void PixelShader( Stage Vertex Shader Pixel Shader Raster // Input per pixel Rasterizer in float2 textureCoordinates, (static and dynamic (static Operations (with Z-Cull) in float3 normal, flow control) flow control only) Unit // Input per batch of triangles Texture uniform sampler2D
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