geometric objects and transformations
DESCRIPTION
Geometric Objects and Transformations. Coordinate systems. http://alt.pluralsight.com/wiki/default.aspx/Craig.DirectX/CoordinateSystemsTutorial.html. Clockwise = Front Face. http://msdn.microsoft.com/en-us/library/ee418867%28VS.85%29.aspx. The DirectX 10 Pipeline. - PowerPoint PPT PresentationTRANSCRIPT
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#