Routines
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45688: Copy Block To Screen
Used by the routines at DrawChangedObjects and DisplayObjectsCarried.
Copies a rectangle from the buffer to the screen, a line at a time.
Input
B Number of lines
C Width in bytes
DE Screen address of the top line of the rectangle
HL Buffer address of the first line
CopyBlockToScreen 45688 PUSH BC Stash the line counter, the screen address and the buffer address on the stack.
45689 PUSH DE
45690 PUSH HL
45691 LD B,0 Clear B, ready for the copy.
45693 LDIR Copy a line of the rectangle to the screen.
45695 POP HL Restore the buffer address from the stack.
45696 LD DE,32 Move HL on to the next line of the buffer by adding 32.
45699 ADD HL,DE
45700 POP DE Restore the screen address from the stack.
Move up to the next pixel line of the screen.
45701 DEC D Move up one pixel line.
45702 LD A,D Invert the high byte of the screen address to test its pixel line bits.
45703 CPL
45704 AND %00000111 Keep only the pixel line bits.
45706 JR NZ,CopyBlockToScreen_Next Jump to CopyBlockToScreen_Next if the line is still in the same character row.
45708 LD A,E Move up one character row.
45709 SUB 32
45711 LD E,A
45712 JR C,CopyBlockToScreen_Next Jump to CopyBlockToScreen_Next if that has crossed into the third above.
45714 LD A,D Otherwise cancel the effect of the borrow on the third, by adding 8 to the high byte.
45715 ADD A,8
45717 LD D,A
CopyBlockToScreen_Next 45718 POP BC Restore the line counter from the stack.
45719 DJNZ CopyBlockToScreen Decrease the line counter and loop until all the lines have been copied.
45721 RET Return.
View the equivalent code in;
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