Routines
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D570: Draw Playfield Border
Used by the routines at Apply_Wave_Border_Colour and RenderHUD.
Draws the rectangular border surrounding the play area. If the units digit of *WaveNumber is 09 the routine returns without drawing. Otherwise it draws full-width horizontal strips at rows 0E and 0F (top edge) via DrawPlayfieldBorderRow, then for each row from 10 to B7 it OR-blits columns 06 07 F8 and F9 (left and right edges), and finally draws full-width strips at rows B8 and B9 (bottom edge) via DrawPlayfieldBorderRow. Called from Erase_Narrow_Entity_Sprite and RenderHUD.
playfield-border
DrawPlayfieldBorder D570 LD A,($C408) A=*WaveNumber (BCD wave number).
D573 AND %00001111 Keep the low decimal digit (AND 0F).
D575 CP $09 Return if the units digit is 09 (no border drawn).
D577 RET Z
D578 LD L,$0E Call DrawPlayfieldBorderRow to draw the top-edge strip at row 0E.
D57A CALL DrawPlayfieldBorderRow
D57D LD L,$0F Call DrawPlayfieldBorderRow to draw the top-edge strip at row 0F.
D57F CALL DrawPlayfieldBorderRow
D582 LD L,$10 L=10 (top row of the framed block).
Left and right edges: for each row 10 to B7 OR-blit columns 06 07 F8 and F9 via PlotCharacterCell_Draw.
DrawPlayfieldBorder_SideColumns D584 LD H,$06 H=06 (left inner column).
D586 PUSH HL Stash HL on the stack.
D587 CALL PlotCharacterCell_Draw Call PlotCharacterCell_Draw.
D58A POP HL Restore HL from the stack.
D58B LD H,$07 H=07 (left inner column + 01).
D58D PUSH HL Stash HL on the stack.
D58E CALL PlotCharacterCell_Draw Call PlotCharacterCell_Draw.
D591 POP HL Restore HL from the stack.
D592 LD H,$F8 H=F8 (right inner column).
D594 PUSH HL Stash HL on the stack.
D595 CALL PlotCharacterCell_Draw Call PlotCharacterCell_Draw.
D598 POP HL Restore HL from the stack.
D599 LD H,$F9 H=F9 (right inner column + 01).
D59B PUSH HL Stash HL on the stack.
D59C CALL PlotCharacterCell_Draw Call PlotCharacterCell_Draw.
D59F POP HL Restore HL from the stack.
D5A0 INC L Increment L (next row).
D5A1 LD A,L Loop back to DrawPlayfieldBorder_SideColumns until all rows are drawn.
D5A2 CP $B8
D5A4 JR NZ,DrawPlayfieldBorder_SideColumns
D5A6 LD L,$B8 Call DrawPlayfieldBorderRow to draw the bottom-edge strip at row B8.
D5A8 CALL DrawPlayfieldBorderRow
D5AB LD L,$B9 Call DrawPlayfieldBorderRow to draw the bottom-edge strip at row B9.
D5AD CALL DrawPlayfieldBorderRow
D5B0 RET Return.
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