From this site: http://www.catalinzima.com/?page%5Fid=14
I've always been confused about how the depth map is calculated.
The vertex shader function calculates position as follows:
VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
{
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
output.TexCoord = input.TexCoord; //pass the texture coordinates further
output.Normal =mul(input.Normal,World); //get normal into world space
output.Depth.x = output.Position.z;
output.Depth.y = output.Position.w;
return output;
}
What are output.Position.z and output.Position.w? I'm not sure as to the maths behind this.
And in the pixel shader there is this line: output.Depth = input.Depth.x / input.Depth.y;
So output.Depth is output.Position.z / outputPOsition.w? Why do we do this?
Finally in the point light shader (http://www.catalinzima.com/?page%5Fid=55) to convert this output to be a position the code is:
//read depth
float depthVal = tex2D(depthSampler,texCoord).r;
//compute screen-space position
float4 position;
position.xy = input.ScreenPosition.xy;
position.z = depthVal;
position.w = 1.0f;
//transform to world space
position = mul(position, InvertViewProjection);
position /= position.w;
again I don't understand this. I sort of see why we use InvertViewProjection as we multiply by the view projection previously, but the whole z and now w being made to equal 1, after which the whole position is divided by w confuses me quite a bit.