MPictureDissolveOut PictureBitmapNum.w,Colour.b,WipeToColour.b ;Do picture-based colour dissolve-out of bitmap

Performs a picture-based dissolve in order to `wipe out' a destination bitmap.
You first have to `use' the destination bitmap with MUseBitmap. Then you specify
the `Picture Bitmap' as a parameter to this command which will be the number of a
chunky Bitmap containing an `effect' picture. The routine will search for the
location of pixels in the effect picture that are of the specified colour. When
it finds one it will draw a pixel at those coordinates in the dest Bitmap to
the colour chosen in WipeToColour.b. Note that the picture bitmap and the dest
bitmap in this operation have to be the same size. To fully wipe-out a whole
picture you should call this command as many times as there are colours in the
effect-picture so that all pixels are eventually wiped. The more colours you
make use of in the effect-picture the longer the wipe will take. Note that the
effect-picture should still be 256-colours even if you only use 64, for example.
To create an effect-picture that produces a nice screenwipe you should create
a simple greyscale gradient in something like Deluxe Paint and then perform
some good image-processing operations on it in something like ImageFX to
distort and mangle the gradient to bring variety into the effect. If the
destination bitmap starts off blank it will just cause the effect to appear in a
new colour rather than removing a graphic.