CS361

1. Week 7 - Friday CS361

2. Last time • What did we talk about last time? • Mipmapping • Summed area tables • Anisotropic filtering

3. Questions?

4. Project 2

5. XNA Shader Examples

6. Effect files • We have been using BasicEffect to achieve most of our shading • BasicEffect gets so much done that it's tempting not to move any further • But more complex effects can be achieved by writing shader code ourselves • To start, right click in your Content project and choose Add > New Item • Choose Effect File from the wizard and name it whatever you want

7. Shader declarations • We need to declare the variables we are going to use at the top of the file • These usually include at least the following (which are already given in the template) • We're also going to add an ambient color and an ambient intensity for this shader float4x4 World; float4x4 View; float4x4 Projection; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1;

8. Shader data structures • We also have to define structures to take the input and the output • These vary because different vertex formats include different data (position, normals, colors, texture coordinates) • The simplest possible input and output would have position only • The POSITION0 is called a semantic • Semantics are used to tell the shader what the purpose of a variable is structVertexShaderInput { float4 Position : POSITION0; }; structVertexShaderOutput { float4 Position : POSITION0; };

9. Vertex shader • The job of the vertex shader is, at the very least, to transform a vertex from model space to world space to view space to clip space • It can also do normal and color calculations, but this first shader will only do the transforms VertexShaderOutputVertexShaderFunction(VertexShaderInput input) { VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View); output.Position = mul(viewPosition, Projection); return output; }

10. Pixel shader • The pixel shader must find the final color of the pixel fragment • This first pixel shader uses an ambient shading model • The ambient shading model is the simplest possible • Everything gets colored the same, no matter where it is float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return AmbientColor * AmbientIntensity; }

11. Techniques • You're allowed to name your vertex and pixel shaders anything you want • You specify which you're going to use in a technique • At this level, techniques only have one pass, but it is possible to use multiple techniques to achieve interesting effects technique Ambient { pass Pass1 { VertexShader = compile vs_2_0 VertexShaderFunction(); PixelShader = compile ps_2_0 PixelShaderFunction(); } }

12. Using the shader in the game • You have to load the shader like other content • Then, we run a loop similar to the earlier one, setting the parameters for the effect object effect = Content.Load<Effect>("Shaders/ambient"); foreach( ModelMeshmesh inmodel.Meshes ) { foreach( ModelMeshPartpart inmesh.MeshParts ) { part.Effect= effect; effect.Parameters["World"].SetValue(world * mesh.ParentBone.Transform); effect.Parameters["View"].SetValue(view); effect.Parameters["Projection"].SetValue(projection); } mesh.Draw(); }

13. The results! • Okay, not that impressive yet • But now we have some idea what we're doing

14. Project 2 Work Time

15. Upcoming

16. Next time… • Materials • Alpha • Bump mapping

17. Reminders • Finish Project 2 • Due tonight by midnight • Read Chapter 7 • Assignment 3 will be assigned over Spring Break