Geometric Objects and Transformations

1. Geometric Objects and Transformations

2. Coordinate systems http://alt.pluralsight.com/wiki/default.aspx/Craig.DirectX/CoordinateSystemsTutorial.html

3. Clockwise = Front Face

4. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 1: Model Space -> World Space

5. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 2: World Space -> Camera Space (Not done in OpenGL 2.x)

6. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 3: Camera Space -> Projection Space

7. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 4: Change the Clipping Matrix (If you are not using the std Projection Matrix)

8. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 5: Clipping (Not a Matrix!)

9. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 6: Projected Space -> Clipping Space (Flips the Y-Axis)

10. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspxhttp://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx The DirectX 10 Pipeline Stage 7: Projected Space -> Screen Space (Coordinates passed to the rasterizer)

11. Up till Dx9 this was all done for us... With the new approach to Rendering, NOTHING is default • Need to write our own: • Geometry Shader (Optional) • Vertex Shader • Pixel Shader • Code to run the Combined Vertex Shader + Pixel Shader on the GPU (Effect)

12. HLSL • High Level Shader Language, the Dx only solution. • Cg, the NvidiaDx / GL solution • GLSL, the GL only solution

13. What about a real Vertex Shader? matrix World; matrix View; matrix Projection; VS_OUTPUT VS( float4 Pos : POSITION, float4 Color : COLOR ) { VS_OUTPUT output = (VS_OUTPUT)0; output.Pos = mul( Pos, World ); output.Pos = mul( output.Pos, View ); output.Pos = mul( output.Pos, Projection ); output.Color = Color; return output; }

14. Our Super Cheap Vertex Shader float4 VS( float4 Pos : POSITION ) : SV_POSITION { return Pos; } The Colon: sets the semantics of the data (metadata)

15. Geometry Shaders WTF? • Grass • Water • Fur +ve Less Bus Data Less CPU + Memory usage -ve More GPU Load No Dx9 or below compatibility (Who cares!)

16. Vertex Shader • Base Functions: • World • View • Projection Transformation • Extensions: • Water Movement • Plant movements • Object Morphing

17. Pixel (Fragment) Shader • Colouring • Simple texturing • Cell shading • Normal mapping • Particle effects • Alpha blending • Etc!

18. Semantics (metadata) • There are so few data types in GPU programming (Typically just a load of floats) • Using Semantics we can specify the intended purpose of the variables • What does this do: • float3 pos : POSITION; • Creates 3x floats to store the xyz + tells HLSL the floats are used as a position

19. Semantics • What about: float4x4 wvp : WORLDVIEWPROJ ...

20. float4 PS( float4 Pos : SV_POSITION ) : SV_Target { return float4( 1.0f, 1.0f, 0.0f, 1.0f ); // BGRA }

21. In both OpenGL and Direct3D Z is the depth of the viewport!!!! hence the Z-buffer (Depth Buffer)

22. Z Buffer Depth • Due to the scalar nature of the Pyramid Viewport • Depth precision drops as the distance between the Near and Far planes are moved apart • This will result in more artefacts and visual errors

23. Viewport types • Orthogonal • No depth perception (scaling) • Projected • This is the typical 3D viewport • Objects \ Vertices are scaled and rotated based on the ‘virtual’ distance from the screen

24. References • http://knol.google.com/k/hlsl-shaders#