Is there anybody knows how to calculate the area of world coordinates for one texel in a shadow map (for dir-light or spot-light)? I just remember some paper has given some MAGIC formula to calculate this, such as:
float calculateSurfelAreaLight(vec3 lightPos)
{
return (4.0 * lightPos.z * lightPos.z * f_tanFovXHalf * f_tanFovYHalf) / (i_RSMsize * i_RSMsize);
}
But i can't find the full induction process about its formula. How can I get this induced formula? What is the relationship between the area and the light-fov? Any suggestions or paper-references about this would be greatly appreciated!