I already have a fragment shader that generates a normal map from a height map. Now I need to apply the effect to all 360 degrees of the rotated heightmap.
Of coarse I could just apply the effect 360 times to each heighmap, but if I have already done it once then is it possible to use what I have to efficiently generate the remaining 359 maps?
Im guessing that each pixel gets offset (in r,g,b) by some constant amount depending on the rotation:
Given the normal that you unpack from the normalmap, I think all you need to do is transform that normal by a matrix that specifies a rotation about the z-axis by the number of degrees you need.
Awesome. It ended up being much simpler than I made it out to be, thanks!
sampler2D input : register(s0);
float degree : register(C0);
float3 rotatedVec(float3 original)
{
float rad = radians( degree);
float3x3 rotationMat =
{
cos( rad), -sin(rad), 0,
sin( rad), cos(rad), 0,
0,0,1
};
return mul( rotationMat , original);
}
float4 main(float2 uv : TEXCOORD) : COLOR
{
float3 norm = normalize(tex2D(input, uv.xy).rgb * 2.0 - 1.0);
float3 newColor = rotatedVec(norm);
newColor = newColor * 0.5 + 0.5;
return float4(newColor,1.0);
}
You could further optimize the shader by calculating the sine (and the cosine) of the rotation angle in CPU and pass it as a shader constant 
