Geometric Objects and Transformations

Coordinate systems

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

Clockwise = Front Face

The DirectX 10 Pipeline

Stage 1: Model Space -> World Space

http://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)

http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx

The DirectX 10 Pipeline

Stage 3: Camera Space -> Projection Space

http://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)

http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx

The DirectX 10 Pipeline

Stage 5: Clipping (Not a Matrix!)

http://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)

http://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)

http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx

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)

HLSL

• High Level Shader Language, the Dx only solution.

• Cg, the Nvidia Dx / GL solution• GLSL, the GL only solution

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;

}

Our Super Cheap Vertex Shader

float4 VS( float4 Pos : POSITION ) : SV_POSITION{ return Pos;}The Colon: sets the semantics of the data

(metadata)

Geometry Shaders WTF?

• Grass• Water• Fur+ve

Less Bus DataLess CPU + Memory usage

-veMore GPU LoadNo Dx9 or below compatibility (Who cares!)

Vertex Shader

• Base Functions:– World– View– Projection Transformation

• Extensions:– Water Movement– Plant movements– Object Morphing

Pixel (Fragment) Shader

• Colouring• Simple texturing• Cell shading• Normal mapping• Particle effects• Alpha blending• Etc!

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

Semantics

• What about:float4x4 wvp : WORLDVIEWPROJ...

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

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

• 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

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

References

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