Please note that the bottom four bits in the pattern are not used by this instruction, and should always be set to zero. Also, that SCREEN COPY combines the source and destination graphics using blitter areas B and C, but not area A. To short-circuit the mass of all 255 options, here is a list of five of the most common modes, along with their binary bit-map patterns, followed by a ready-made working example to examine:
Mode Bit-pattern Effect
REPLACE %11000000 Replace destination graphics with a copy of the
source image. (Default mode.)
INVERT %00110000 Replace destination graphics with an inverse
video image of the source.
AND %10000000 Combine together the source and destination
images, with a logical AND operation.
OR %11100000 Overlap the source image with the destination
graphics.
XOR %011000000 Combine together an inverse source image and
destination graphics, with an Exclusive OR.
Examine that demonstration program, and use the mouse pointer to copy the image anywhere on screen, with a single click of the left mouse button. Keep the button held down and move the mouse pointer to see the full potential of SCREEN COPY, then press any key to call up the next mask and repeat the process.
Scrolling the screen
DEF SCROLL
instruction: define a scrolling screen zone
Def Scroll number,x1,y1 To x2,y2,horizontal value, vertical value
Using the AMOS Professional system, you are able to define up to 16 different scrolling screen zones, and each one can have an individual pattern of movement. Simply follow your DEF SCROLL command with the number from 1 to 16 of the zone you are setting up. Then give the coordinates of the area of the zone to be scrolled, from the top left-hand corner to the diagonally opposite bottom right-hand corner. Finally, give this zone a scrolling pattern by setting the number of pixels to be shifted horizontally, and the number of pixels to be shifted vertically during each scrolling operation. Positive horizontal values will cause a shift to the right whereas negative values will shift the zone towards the left of the screen. Similarly, positive vertical values will scroll downwards and negative values cause an upward scroll.
SCROLL
instruction: scroll a screen zone
Scroll zone number
To scroll a screen zone already specified with a DEF SCROLL setting, use SCROLL followed by the zone number you require.