For a spot lamp I have two angles -- angle of the outer cone (spot size) and angle of the inner cone that inidicates the boundary line at which light from the spot will start to blur. Based on these two angles how can I calculate "blend" of the spot?
Blender reference manual says that "blend" value can be between 0.0 and 1.0 and that:
The falloff rate of the Spot lamp light is a ratio between the Blend and Size values; the larger the circular gap between the two, the more gradual the light fades between Blend and Size.
But I can't figure out the exact formula to calculate blend based on those two angles.