BeamShader.RFC

REQUEST FOR COMMENTS: BEAM SHADER

The beam shader is a GPU shader  (texture: GLtexture; x,y: REAL: di,dj: INTEGER; nx,ny,nz: REAL; ra, ga, ba, dot: REAL) --> ARRAY di,dx OF GLPixel  [pseudocode] 

texture: previously loaded
x,y: a position in the texture unit rectangle (unit because the whole texture is on [0,1][0,1], rectangle because the texture need not be square) 
di,dj: size of result patch
nx,ny,nz: normal vector of texture plane to beam
ra,ga,ba,dot: alpha multiplicands

Intuition: Any math should be performed here on the GPU side rather than before the call if it can be.

BEGIN
	Project the result patch (a rectangle di*dj) onto the texture according to the normal (foreshortening)
	Fill the result patch with pixels from the texture
	For each pixel p:
		p.red:= p.red*ra*dot;
		p.green:=p.green*dot;
		p.blue:=p.blue*dot;
	END
END

The input to the shader is in the form of an array W,H of records (texture: GLtexture; x,y: REAL: di,dj: INTEGER; nx,ny,nz: REAL; ra, ga, ba, dot: REAL)
The output is in the form of an array W*N,W*M of pixels, ie a texture
If di and dj are equal for all records (beams) then the output array is made up of tiles of equal size 

The shader runs once per frame.