How a projector's color combines with what's already on the target.
'alpha'
dst = mix(dst, src, src.a * opacity)
'add'
dst += src * opacity
'multiply'
dst *= mix(1, src, opacity)
How a projector's color combines with what's already on the target.
'alpha'—dst = mix(dst, src, src.a * opacity); the usual sticker / slide look.'add'—dst += src * opacity; light-projector / caustic look.'multiply'—dst *= mix(1, src, opacity); gobo / stain look.