Week 3 - Monday

 What did we talk about last time?  Graphics rendering pipeline  Rasterizer Stage

 An effect says how things should be rendered on the screen  We can specify this in details using shader programs  The BasicEffect class gives you the ability to do effects without creating a shader program  Less flexibility, but quick and easy  The BasicEffect class has properties for:  World transform  View transform  Projection transform  Texture to be applied  Lighting  Fog

 Vertices can be stored in many different formats depending on data you want to keep  Position is pretty standard  Normals are optional  Color is optional  We will commonly use the VertexPositionColor type to hold vertices with color

 The GPU holds vertices in a buffer that can be indexed into  Because it is special purpose hardware, it has to be accessed in special ways  It seems cumbersome, but we will often create an array of vertices, create an appropriately sized vertex buffer, and then store the vertices into the buffer VertexPositionColor[] vertices = new VertexPositionColor[3] { new VertexPositionColor(new Vector3(0, 1, 0), Color.Red), new VertexPositionColor(new Vector3(+0.5f, 0, 0), Color.Green), new VertexPositionColor(new Vector3(-0.5f, 0, 0), Color.Blue) }; vertexBuffer = Buffer.New (GraphicsDevice, 3, BufferFlags.VertexBuffer); vertexBuffer.SetData (vertices); inputLayout = VertexInputLayout.New (0); VertexPositionColor[] vertices = new VertexPositionColor[3] { new VertexPositionColor(new Vector3(0, 1, 0), Color.Red), new VertexPositionColor(new Vector3(+0.5f, 0, 0), Color.Green), new VertexPositionColor(new Vector3(-0.5f, 0, 0), Color.Blue) }; vertexBuffer = Buffer.New (GraphicsDevice, 3, BufferFlags.VertexBuffer); vertexBuffer.SetData (vertices); inputLayout = VertexInputLayout.New (0);

 In order to draw a vertex buffer, you have to:  Set the basic effect to have the appropriate transformations  Set the vertex buffer on the device as the current one being drawn  Set the vertex input layout so that the device knows what's in the vertex buffer  Loop over the passes in the basic effect, applying them  Draw the appropriate kind of primitives basicEffect.World = world; basicEffect.View = view; basicEffect.Projection = projection; GraphicsDevice.SetVertexBuffer (vertexBuffer); GraphicsDevice.SetVertexInputLayout(inputLayout); foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.Draw(PrimitiveType.TriangleList, 3); } basicEffect.World = world; basicEffect.View = view; basicEffect.Projection = projection; GraphicsDevice.SetVertexBuffer (vertexBuffer); GraphicsDevice.SetVertexInputLayout(inputLayout); foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.Draw(PrimitiveType.TriangleList, 3); }

 Sometimes a mesh will repeat many vertices  Instead of repeating those vertices, we can give a list of indexes into the vertex list instead short[] indices = new short[3] { 0, 1, 2}; indexBuffer = Buffer.New (GraphicsDevice, 3, BufferFlags.IndexBuffer); indexBuffer.SetData (indices); short[] indices = new short[3] { 0, 1, 2}; indexBuffer = Buffer.New (GraphicsDevice, 3, BufferFlags.IndexBuffer); indexBuffer.SetData (indices);

 Once you have the index buffer, drawing with it is very similar to drawing without it  You simply have to set it on the device  The false means that the indexes are short values instead of int values  Then call DrawIndexed() instead of Draw() on the device basicEffect.World = world; basicEffect.View = view; basicEffect.Projection = projection; GraphicsDevice.SetVertexBuffer (vertexBuffer); GraphicsDevice.SetVertexInputLayout(inputLayout); GraphicsDevice.SetIndexBuffer(indexBuffer, false); foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.DrawIndexed(PrimitiveType.TriangleList, 3); } basicEffect.World = world; basicEffect.View = view; basicEffect.Projection = projection; GraphicsDevice.SetVertexBuffer (vertexBuffer); GraphicsDevice.SetVertexInputLayout(inputLayout); GraphicsDevice.SetIndexBuffer(indexBuffer, false); foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.DrawIndexed(PrimitiveType.TriangleList, 3); }

 An icosahedron has 20 sides, but it only has 12 vertices  By using an index buffer, we can use only 12 vertices and 60 indices  Check out the XNA tutorial on RB Whitaker's site for the data:   There are some minor changes needed to make the code work

 It is very common to define primitives in terms of lists and strips  A list gives all the vertex indices for each of the shapes drawn  2n indices to draw n lines  3n indices to draw n triangles  A strip gives only the needed information to draw a series of connected primitives  n + 1 indices to draw a connected series of n lines  n + 2 indices to draw a connected series of n triangles

 GPU stands for graphics processing unit  The term was coined by NVIDIA in 1999 to differentiate the GeForce256 from chips that did not have hardware vertex processing  Dedicated 3D hardware was just becoming the norm and many enthusiasts used an add- on board in addition to their normal 2D graphics card  Voodoo2

 Modern GPU's are generally responsible for the geometry and rasterization stages of the overall rendering pipeline  The following shows colored-coded functional stages inside those stages  Red is fully programmable  Purple is configurable  Blue is not programmable at all Vertex Shader Geometry Shader Clipping Screen Mapping Triangle Setup Triangle Traversal Pixel Shader Merger

 You can do all kinds of interesting things with programmable shading, but the technology is still evolving  Modern shader stages such as Shader Model 4.0 and 5.0 (DirectX 10 and 11) use a common-shader core  Strange as it may seem, this means that vertex, pixel, and geometry shading uses the same language

 They are generally C-like  There aren't that many:  HLSL: High Level Shading Language, developed by Microsoft and used for Shader Model 1.0 through 5.0  Cg: C for Graphics, developed by NVIDIA and is essentially the same as HLSL  GLSL: OpenGL Shading Language, developed for OpenGL and shares some similarities with the other two  These languages were developed so that you don't have to write assembly to program your graphics cards  There are even drag and drop applications like NVIDIA's Mental Mill

 To maximize compatibility across many different graphics cards, shader languages are thought of as targeting a virtual machine with certain capabilities  This VM is assumed to have 4-way SIMD (single- instruction multiple-data) parallelism  Vectors of 4 things are very common in graphics:  Positions: xyzw  Colors: rgba  The vectors are commonly of float values  Swizzling and masking (duplicating or ignoring) vector values are supported (kind of like bitwise operations)

 A programmable shader stage has two types of inputs  Uniform inputs that stay constant during draw calls ▪ Held in constant registers or constant buffers  Varying inputs which are different for each vertex or pixel

 Fast operations: scalar and vector multiplications, additions, and combinations  Well-supported (and still relatively fast): reciprocal, square root, trig functions, exponentiation and log  Standard operations apply: + and *  Other operations come through intrinsic functions that do not require headers or libraries: atan(), dot(), log()  Flow control is done through "normal" if, switch, while, and for (but long loops are unusual)

 In 1984, Cook came up with the idea of shade trees, a series of operations used to color a pixel  This example shows what the shader language equivalent of the shade tree is

 There are three shaders you can program  Vertex shader  Useful, but boring, mostly about doing transforms and getting normals  Geometry shader  Optional, allows you to create vertices from nowhere in hardware  Pixel shader  Where all the color data gets decided on  Also where we'll focus

 The following, taken from RB Whitaker's Wiki, shows a shader for ambient lighting  We start with declarations: float4x4 World; float4x4 View; float4x4 Projection; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1; struct VertexShaderInput { float4 Position : POSITION0; }; struct VertexShaderOutput { float4 Position : POSITION0; }; float4x4 World; float4x4 View; float4x4 Projection; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1; struct VertexShaderInput { float4 Position : POSITION0; }; struct VertexShaderOutput { float4 Position : POSITION0; };

VertexShaderOutput VertexShaderFunction(VertexShaderInput input) { VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return AmbientColor * AmbientIntensity; } technique Ambient { pass Pass1 { VertexShader = compile vs_1_1 VertexShaderFunction(); PixelShader = compile ps_1_1 PixelShaderFunction(); } VertexShaderOutput VertexShaderFunction(VertexShaderInput input) { VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return AmbientColor * AmbientIntensity; } technique Ambient { pass Pass1 { VertexShader = compile vs_1_1 VertexShaderFunction(); PixelShader = compile ps_1_1 PixelShaderFunction(); }

The result, applied to a helicopter model:

 The following, taken from RB Whitaker's Wiki, shows a shader for diffuse lighting float4x4 World; float4x4 View; float4x4 Projection; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1; float4x4 WorldInverseTranspose; float3 DiffuseLightDirection = float3(1, 0, 0); float4 DiffuseColor = float4(1, 1, 1, 1); float DiffuseIntensity = 1.0; struct VertexShaderInput { float4 Position : POSITION0; float4 Normal : NORMAL0; }; struct VertexShaderOutput { float4 Position : POSITION0; float4 Color : COLOR0; }; float4x4 World; float4x4 View; float4x4 Projection; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1; float4x4 WorldInverseTranspose; float3 DiffuseLightDirection = float3(1, 0, 0); float4 DiffuseColor = float4(1, 1, 1, 1); float DiffuseIntensity = 1.0; struct VertexShaderInput { float4 Position : POSITION0; float4 Normal : NORMAL0; }; struct VertexShaderOutput { float4 Position : POSITION0; float4 Color : COLOR0; };

VertexShaderOutput VertexShaderFunction(VertexShaderInput input){ VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); float4 normal = mul(input.Normal, WorldInverseTranspose); float lightIntensity = dot(normal, DiffuseLightDirection); output.Color = saturate(DiffuseColor * DiffuseIntensity * lightIntensity); return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return saturate(input.Color + AmbientColor * AmbientIntensity); } technique Diffuse { pass Pass1 { VertexShader = compile vs_1_1 VertexShaderFunction(); PixelShader = compile ps_1_1 PixelShaderFunction(); } VertexShaderOutput VertexShaderFunction(VertexShaderInput input){ VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); float4 normal = mul(input.Normal, WorldInverseTranspose); float lightIntensity = dot(normal, DiffuseLightDirection); output.Color = saturate(DiffuseColor * DiffuseIntensity * lightIntensity); return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return saturate(input.Color + AmbientColor * AmbientIntensity); } technique Diffuse { pass Pass1 { VertexShader = compile vs_1_1 VertexShaderFunction(); PixelShader = compile ps_1_1 PixelShaderFunction(); }

The result, applied to a helicopter model:

 GPU architecture  Vertex shading  Geometry shading  Pixel shading

 Keep reading Chapter 3  Keep working on Assignment 1, due this Friday by 11:59  Keep working on Project 1, due next Friday, February 6 by 11:59