Other Spreadsheet functions
Blend function: blend_op( Ca, Cb, Ka , Kb)
= Ca * Ka + Cb * Kb (all parameters must be between 0,1)
Clamp function: clamp (val, min, max)
Will clamp val between min and max values
lod_adjust function: lod_adjust(val, lod)
= val >> int(lod) (shift val left by lod amount)
This function is useful for calculating width, height of new texture
map given the LOD and width, height of Zero-level texture map.