By changing these planes, selected colours can be omitted from the Bob when it is drawn on screen. For example:
X Set Bob 1,0,$000111 : Rem Display bits drawn in colours 0 to 7 Set Bob 1,0,$111111 : Rem Display all bit-planes
The last SET BOB parameter is another bit pattern, that selects one of 255 possible Miler modes used to draw Bobs on screen. This can set a mask, so that colour zero is transparent, and a full description of the available modes is given at the beginning of Chapter 6.2, in the SCREEN COPY section. In fact, the mask parameter is usually set to one of two values:
%11100010 if no mask is to be used.
%11001010 if the Bob is to be used with a mask, in other words, if colour zero is to be transparent.
So the following line would set Bob 1 moving across the original screen colours, with a mask set:
E> Set Bob 1,0,%111111, %11001010
Advanced users may find the following information useful:
Blitter Source Purpose A Blitter Mask B Blitter Object C Destination Screen