Routines
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50758: Draw Overlapped Block
Draws a block in the parts left uncovered by entities drawn earlier. Those entities are in the table at 45491, four bytes each, and the count is patched into this routine. Each item that covers the row leaves a span, which DrawBlockSpan draws.
The two limits of the row are remembered, and the count of overlapping items is patched into the loop.
DrawOverlappedBlock 50758 LD (50775),HL Remember the first limit.
50761 LD (50816),DE Remember the second limit.
50765 EXX Use the limits' register set.
50766 LD IX,45491 Start at the first overlapping item.
50770 LD B,0 The number of items is patched.
50772 AND A Clear the carry for the comparison.
DrawOverlappedBlock_Loop 50773 PUSH BC Remember how many items remain.
50774 LD HL,0 Read the patched first limit.
50777 LD A,L Take its low byte.
50778 AND %11111000 Use the patched mask.
50780 OR %00000000 Apply the patched bits.
50782 LD L,A Remember the masked limit.
50783 LD (51117),A
50786 LD D,128 Take the item's first byte, with the patched high byte.
50788 LD E,(IX+0)
50791 SBC HL,DE Subtract it from the limit.
50793 JR C,DrawOverlappedBlock_Above The item starts above the row.
50795 LD A,H The item is a whole byte or more past the row.
50796 AND A
50797 JR NZ,DrawOverlappedBlock_Next
50799 LD A,L The gap is at least the item's next byte.
50800 SUB (IX+2)
50803 JR NC,DrawOverlappedBlock_Next
50805 JR DrawOverlappedBlock_Second Join the second limit.
DrawOverlappedBlock_Above 50807 INC H The other side is a whole byte or more away.
50808 JR NZ,DrawOverlappedBlock_Next
50810 LD A,L The item's extra size does not reach the row.
50811 ADD A,0
50813 JR NC,DrawOverlappedBlock_Next
DrawOverlappedBlock_Second 50815 LD HL,0 Read the patched second limit.
50818 SLA H The high byte has to be clear.
50820 JR NZ,DrawOverlappedBlock_Next
50822 LD A,L The low byte has to reach the patched edge.
50823 SUB 0
50825 JR C,DrawOverlappedBlock_Height
50827 INC A Shift that distance up.
50828 RLA
50829 JR C,DrawOverlappedBlock_Next A distance that overflowed does not cover the row.
DrawOverlappedBlock_Height 50831 LD B,(IY+6) Read the shape's position byte.
50834 LD A,L Subtract the item's byte from the distance.
50835 SUB (IX+1)
50838 JR C,DrawOverlappedBlock_Far The item covers the far side of the row.
50840 LD H,A The remainder is the height so far.
50841 SUB 0 A remainder past the patched edge does not cover the row.
50843 JR NC,DrawOverlappedBlock_Next
50845 LD L,(IX+1) The height is the item's byte, negated.
50848 NEG
50850 LD B,A
50851 CP (IX+3) Use the smaller of that height and the item's other byte.
50854 JR C,DrawOverlappedBlock_Draw
50856 LD B,(IX+3) Use the item's byte when it is the smaller.
50859 JR DrawOverlappedBlock_Draw
DrawOverlappedBlock_Far 50861 ADD A,(IX+3) Add the item's byte to the distance.
50864 JR NC,DrawOverlappedBlock_Next The sum has to reach past zero.
50866 JR Z,DrawOverlappedBlock_Next
50868 CP 0 Use the patched edge when the sum is below it.
50870 JR NC,DrawOverlappedBlock_Draw
50872 LD B,A The height is that sum.
DrawOverlappedBlock_Draw 50873 CALL DrawBlockSpan Draw the span that this item leaves.
DrawOverlappedBlock_Next 50876 LD BC,4 Move on to the next item.
50879 ADD IX,BC
50881 POP BC Bring the count back.
50882 DJNZ DrawOverlappedBlock_Loop Repeat for the remaining items.
50884 RET Return.
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