Routines
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95B6: Stamp Terrain Tile
Write crater tiles into TerrainData_Active under the current actor and redraw them on the screen.
Input
IX Actor slot
StampTerrainTile 95B6 CALL ReadTerrainCell Call ReadTerrainCell.
95B9 PUSH HL Stash the cell index on the stack.
95BA LD DE,$7000 DE=TerrainData_Active.
95BD EX DE,HL Switch the DE and HL registers.
95BE ADD HL,DE Point HL at that terrain cell.
95BF BIT 3,(HL) Jump to StampTerrainTile_WriteFirstCell if bit 3 of the tile is reset.
95C1 JR Z,StampTerrainTile_WriteFirstCell
95C3 LD (HL),$0A Write 0A to the cell. udg63166_67x4
95C5 JR StampTerrainTile_Neighbour Jump to StampTerrainTile_Neighbour.
StampTerrainTile_WriteFirstCell 95C7 LD (HL),$08 Write 08 to the cell. udg63150_67x4
Stamp the neighbouring cell.
StampTerrainTile_Neighbour 95C9 INC DE Move onto the next cell.
95CA LD A,D Fetch the high byte.
95CB AND %00000011 Keep only bits 0-1.
95CD LD D,A Write it back to D.
95CE LD HL,$7000 HL=TerrainData_Active.
95D1 ADD HL,DE Point HL at that terrain cell.
Pick the tile for the neighbouring cell: 0A if bit 3 is set, else 09.
95D2 BIT 3,(HL) Jump to StampTerrainTile_WriteSecondCell if bit 3 of the tile is reset.
95D4 JR Z,StampTerrainTile_WriteSecondCell
95D6 LD (HL),$0A Write 0A to the cell. udg63166_67x4
95D8 JR StampTerrainTile_Redraw Jump to StampTerrainTile_Redraw.
StampTerrainTile_WriteSecondCell 95DA LD (HL),$09 Write 09 to the cell. udg63158_67x4
Redraw the stamped columns onto the play area.
StampTerrainTile_Redraw 95DC CALL ClearTerrainUnderActor Jump to StampTerrainTile_Restore if ClearTerrainUnderActor returns non-zero.
95DF JP NZ,StampTerrainTile_Restore
95E2 LD A,H Subtract 08 from the high byte.
95E3 SUB $08
95E5 LD H,A Write it back to H.
Wrap the cell index and point DE at its terrain cell.
95E6 EX (SP),HL Exchange the cell index with the stacked pointer.
95E7 LD A,H Fetch the high byte.
95E8 AND %00011111 Keep only bits 0-4.
95EA LD H,A Write it back to H.
95EB LD DE,$7000 DE=TerrainData_Active.
95EE EX DE,HL Point DE at that terrain cell.
95EF ADD HL,DE
95F0 EX DE,HL
95F1 EX (SP),HL Exchange the cell index with the stacked pointer.
Move onto the next screen column if the scroll is on a character boundary.
95F2 LD A,($607A) Fetch Jetman_Position.
95F5 AND %00000111 Keep only bits 0-2.
95F7 JR NZ,StampTerrainTile_XORColumn Jump to StampTerrainTile_XORColumn if the scroll is not on a character boundary, else move onto the next screen column.
95F9 INC HL
OR the first graphic column onto the screen.
StampTerrainTile_XORColumn 95FA PUSH HL Stash the screen pointer on the stack.
95FB LD A,(DE) Fetch the tile index from *DE into HL.
95FC LD L,A
95FD LD H,$00
95FF LD DE,$F66E DE=TerrainUDGs.
9602 ADD HL,HL Multiply the tile index by 08 and add the graphic base.
9603 ADD HL,HL
9604 ADD HL,HL
9605 ADD HL,DE
9606 EX DE,HL Point DE at that graphic.
Work out the pixel shift from the scroll position.
9607 EXX Switch to the shadow registers.
9608 LD A,($607A) Fetch Jetman_Position.
960B NEG Negate the low byte.
960D AND %00000111 Keep only bits 0-2.
960F LD C,A Store the pixel shift in C.
9610 EXX Switch back to the main registers.
9611 POP HL Restore the screen pointer from the stack, but stash a copy of it on the stack again.
9612 PUSH HL
9613 LD B,$08 Set a pixel row counter in B for 08 loops.
9615 CALL StampTerrainTile_Loop Call StampTerrainTile_Loop.
Fetch the next terrain cell's graphic and draw it in the next screen column.
9618 POP HL Restore the screen pointer from the stack.
9619 EX (SP),HL Exchange it with the stacked cell index.
961A INC HL Move onto the next cell.
961B LD A,H Fetch the high byte.
961C AND %00000011 Keep only bits 0-1.
961E LD H,A Write it back to H.
Look up the graphic for that cell.
961F LD DE,$7000 DE=TerrainData_Active.
9622 ADD HL,DE Point HL at that terrain cell.
9623 LD L,(HL) Fetch the tile index from *HL into HL.
9624 LD H,$00
9626 ADD HL,HL Multiply the tile index by 08.
9627 ADD HL,HL
9628 ADD HL,HL
9629 LD DE,$F66E DE=TerrainUDGs.
962C ADD HL,DE Point DE at that graphic.
962D EX DE,HL
Aim at the next screen column and reset the row counter.
962E POP HL Restore the screen pointer from the stack.
962F INC L Move onto the next screen column.
9630 LD B,$08 Set a pixel row counter in B for 08 loops.
Shift a graphic byte by the scroll and OR it onto two neighbouring screen bytes.
StampTerrainTile_Loop 9632 LD A,(DE) Fetch the graphic byte.
9633 EXX Switch to the shadow registers.
9634 LD H,A Store it in H and clear L.
9635 LD L,$00
9637 LD B,C B=the pixel shift.
9638 LD A,C Jump to StampTerrainTile_MergeBytes if there is no shift.
9639 AND A
963A JR Z,StampTerrainTile_MergeBytes
StampTerrainTile_ShiftPixel 963C SRL H Shift the graphic right by one pixel.
963E RR L
9640 DJNZ StampTerrainTile_ShiftPixel Decrease the shift counter by one and loop back to StampTerrainTile_ShiftPixel until the shift is done.
OR the shifted graphic onto the two screen bytes.
StampTerrainTile_MergeBytes 9642 LD A,L Stash the low byte and fetch the high byte.
9643 EX AF,AF'
9644 LD A,H
9645 EXX Switch back to the main registers.
9646 OR (HL) Merge the high byte onto the current screen byte.
9647 LD (HL),A
9648 INC L
9649 EX AF,AF' Fetch the stashed low byte.
964A OR (HL) Merge the low byte onto the next screen byte.
964B LD (HL),A
964C INC DE Move onto the next graphic byte.
964D DEC L Step back and down one pixel row.
964E INC H
964F DJNZ StampTerrainTile_Loop Decrease the row counter by one and loop back to StampTerrainTile_Loop until the column is drawn.
9651 RET Return.
StampTerrainTile_Restore 9652 POP HL Restore the cell index from the stack.
9653 RET Return.
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