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Week 3 - Monday. CS361. Last time. What did we talk about last time? Graphics rendering pipeline Rasterizer Stage. Questions?. Project 1. Assignment 1. XNA Drawing Primitives. The BasicEffect class. An effect says how things should be rendered on the screen
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Week 3 - Monday CS361
Last time • What did we talk about last time? • Graphics rendering pipeline • Rasterizer Stage
The BasicEffect class • 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 • 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
Vertex buffers • 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 = newVertexPositionColor[3] { newVertexPositionColor(new Vector3(0, 1, 0), Color.Red), newVertexPositionColor(new Vector3(+0.5f, 0, 0), Color.Green), newVertexPositionColor(new Vector3(-0.5f, 0, 0), Color.Blue) }; vertexBuffer = newVertexBuffer(GraphicsDevice, typeof(VertexPositionColor), 3, BufferUsage.WriteOnly); vertexBuffer.SetData<VertexPositionColor>(vertices);
Vertices • We will define a list of vertices • Then we will define primitives with lists of indices into that list VertexPositionColor[] vertices = newVertexPositionColor[3] { newVertexPositionColor(new Vector3(0, 1, 0), Color.Red), newVertexPositionColor(new Vector3(+0.5f, 0, 0), Color.Green), newVertexPositionColor(new Vector3(-0.5f, 0, 0), Color.Blue) }; short[] indices = new short[3] { 0, 1, 2};
Drawing an icosahedron • 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
Lists and strips • 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 • 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
More pipes! • 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
Programmable Shaders • 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
Shading languages • 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
Virtual machines • 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)
Programming model • 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
Language style • 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)
Where the idea comes from • 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
Shaders • 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
Example of real shadercode • 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; structVertexShaderInput { float4 Position : POSITION0; }; structVertexShaderOutput { float4 Position : POSITION0; };
Example of real shader code continued VertexShaderOutputVertexShaderFunction(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(); } }
More advanced shader code • 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; structVertexShaderInput { float4 Position : POSITION0; float4 Normal : NORMAL0; }; structVertexShaderOutput { float4 Position : POSITION0; float4 Color : COLOR0; };
More advanced shader code continued VertexShaderOutputVertexShaderFunction(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(); } }
Next time… • GPU architecture • Vertex shading • Geometry shading • Pixel shading
Reminders • Keep reading Chapter 3 • Keep working on Assignment 1, due this Friday by 11:59 • Keep working on Project 1, due next Friday, February 8 by 11:59 • Programming Club tonight at 6pm in E281!