Routines
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58535: Draw Three Byte Rows
Draws a piece of terrain that is three bytes wide, going up the screen two pixel rows at a time, using three words of the picture for each pair of rows. The entry points at DrawThreeByteRows and DrawThreeByteRows_Two first move to the right by three columns and two columns.
Input
A Number of pairs of pixel rows to draw
HL Screen address of the bottom left of the piece
SP Address of the picture
DrawThreeByteRows 58535 INC L Advance L.
DrawThreeByteRows_Two 58536 INC L Advance L.
58537 INC L Advance L.
58538 LD B,A B=A.
DrawThreeByteRows_Loop 58539 POP DE Bring DE back off the stack.
58540 LD (HL),E Write E where HL points.
58541 INC L Advance L.
58542 LD (HL),D Write D where HL points.
58543 INC L Advance L.
58544 POP DE Bring DE back off the stack.
58545 LD (HL),E Write E where HL points.
58546 DEC H Step H back.
58547 LD (HL),D Write D where HL points.
58548 DEC L Step L back.
58549 POP DE Bring DE back off the stack.
58550 LD (HL),E Write E where HL points.
58551 DEC L Step L back.
58552 LD (HL),D Write D where HL points.
58553 DEC H Step H back.
58554 LD A,H A=H.
58555 INC A Advance A.
58556 AND %00000111 Keep the bits of A that are set in 7.
58558 JR NZ,DrawThreeByteRows_Next Jump to DrawThreeByteRows_Next if the zero flag is clear.
58560 LD A,L A=L.
58561 SUB 32 Subtract 32 from A.
58563 LD L,A L=A.
58564 JR C,DrawThreeByteRows_Next Jump to DrawThreeByteRows_Next if the carry flag is set.
58566 LD A,H A=H.
58567 ADD A,8 Add 8 to A.
58569 LD H,A H=A.
DrawThreeByteRows_Next 58570 DJNZ DrawThreeByteRows_Loop Decrease B and jump to DrawThreeByteRows_Loop until none remain.
58572 JP FinishStep Jump to FinishStep.
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