Updated scene shader
 * less-transparent pixes (with alpha > 0.1) substitute texture color (i.e. laser projection, as it worked before, but without color invertion)
 * almost-transparent pixels (with alpha <= 0.1) are added to texture color with the same RGB value and alpha=1 (i.e. work as light source, noo invertion needed)
 * opaque white (1,1,1,1) and transparent black (0,0,0,0) do not affect projection in any way

Known limitations:
 * Inability to project opaque white laser, but can be done by setting RGB values or alpha value to 0.996078431 (254 in integer notation).