BITMAP SCALING TRANSPARENCY OPERATIONS
IBitmapScale must rely on the caller to specify if the source image supports transparency. If it doesn't, IBitmapScale_Scale() can ignore the alpha channel and do the scale in less time. If it does, IBitmapScale_Scale() has to create an alpha channel if needed and consider it while combining pixels to make sure transparency is preserved.
AEEBITMAPSCALE_OPAQUE: The source image does not support transparency AEEBITMAPSCALE_ALPHA: The source image has an alpha channel AEEBITMAPSCALE_KEYCOLOR: The source image has a transparent color