Routines
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928D: Set screen attributes for sprite area.
Fills rectangular regions of attribute cells for both old (erase) and new (draw) sprite positions.
Algorithm: For each position (old then new), calculate the top-left attribute address, then fill a rectangle of B rows × C columns with attribute value A. After filling each row, advance HL by stride DE to reach the next row's starting column.
Input
A Sprite width in tiles (columns to fill).
DE Sprite height in pixels (D), attribute color byte (E).
BC Old position coordinates from previous_object_coordinates.
HL New position coordinates from object_coordinates.
set_sprite_attributes 928D PUSH HL Save registers, store width to attr_sprite_width.
928E PUSH BC
928F LD ($928B),A
9292 LD A,E
9293 CP $00 If ATTRIBUTES_INHERIT, leave existing screen attributes unchanged.
9295 JP Z,handle_zero_attributes
9298 LD ($9287),DE Save DE, BC, HL to memory at attr_saved_de, attr_saved_bc, attr_saved_hl for later use.
929C LD ($9285),BC
92A0 LD ($9289),HL
92A3 LD BC,($8B0A) Calculate attribute address for old position: HL = screen_attributes + (Y AND $F8) * 4 + (X >> 3). Y coordinate is in B of stored BC at previous_object_coordinates, X in C.
92A7 LD A,B
92A8 AND $F8
92AA LD H,$00
92AC LD L,A
92AD ADD HL,HL
92AE ADD HL,HL
92AF LD DE,$5800
92B2 ADD HL,DE
92B3 LD D,$00
92B5 LD E,C
92B6 SRL E
92B8 SRL E
92BA SRL E
92BC ADD HL,DE
92BD LD A,($928B) Calculate row count B = (height >> 3) + 3. This covers sprite height plus padding. Load width into C.
92C0 LD C,A
92C1 LD DE,($9287)
92C5 LD A,D
92C6 SRL A
92C8 SRL A
92CA SRL A
92CC INC A
92CD INC A
92CE INC A
92CF LD B,A Calculate row stride DE = $20 - width. After filling C columns, add DE to reach column 0 of next row. Check if Y is at screen top (row 0).
92D0 EX DE,HL
92D1 LD HL,$0020
92D4 PUSH BC
92D5 LD B,$00
92D7 OR A
92D8 SBC HL,BC
92DA EX DE,HL
92DB LD BC,($8B0A)
92DF LD A,B
92E0 AND $F8 If at screen top (Y AND $F8 = 0), use wrapped fill at set_attr_wrap_old to handle attribute area start.
92E2 CP $00
92E4 LD A,$0C
92E6 JP Z,set_attr_wrap_old
92E9 POP BC
This entry point is used by the routine at set_attr_wrap_old.
set_attr_old_outer_loop 92EA PUSH BC Outer loop start: push BC to preserve row count (B) and column count (C) for this row.
set_attr_old_inner_loop 92EB LD (HL),A Inner loop: write attribute byte A to address HL, increment HL, decrement column counter C, repeat until row complete.
92EC INC HL
92ED DEC C
92EE JR NZ,set_attr_old_inner_loop
92F0 PUSH HL Boundary check: compare HL against screen_attributes_row_16 (row 16 of attributes). If HL >= screen_attributes_row_16, sprite has scrolled off visible area, exit early via attr_old_exit_early.
92F1 LD BC,$5A20
92F4 OR A
92F5 SBC HL,BC
92F7 POP HL
92F8 JP P,attr_old_exit_early
92FB POP BC Row complete: restore BC, add stride DE to HL (moves to same column on next row), decrement row counter B, repeat outer loop.
92FC ADD HL,DE
92FD DJNZ set_attr_old_outer_loop
This entry point is used by the routine at attr_old_exit_early.
set_attr_new_position_entry 92FF LD BC,($8B0C) Calculate attribute address for new position: HL = screen_attributes + (Y AND $F8) * 4 + (X >> 3) using coordinates from object_coordinates.
9303 LD A,B
9304 AND $F8
9306 LD H,$00
9308 LD L,A
9309 ADD HL,HL
930A ADD HL,HL
930B LD DE,$5800
930E ADD HL,DE
930F LD D,$00
9311 LD E,C
9312 SRL E
9314 SRL E
9316 SRL E
9318 ADD HL,DE Calculate row count B = (height >> 3) + 2 (one less row than old position). Load width into C.
9319 LD A,($928B)
931C LD C,A
931D LD DE,($9287)
9321 LD A,D
9322 SRL A
9324 SRL A
9326 SRL A
9328 INC A
9329 INC A Calculate row stride DE = $20 - width. Check if Y is at screen top.
932A LD B,A
932B EX DE,HL
932C LD HL,$0020
932F PUSH BC
9330 LD B,$00
9332 OR A
9333 SBC HL,BC
9335 EX DE,HL
9336 LD BC,($8B0C)
933A LD A,B
933B AND $F8 If at screen top, use wrapped fill at set_attr_wrap_new.
933D CP $00
933F LD BC,($9287)
9343 LD A,C
9344 JP Z,set_attr_wrap_new
9347 POP BC
This entry point is used by the routine at set_attr_wrap_new.
set_attr_new_outer_loop 9348 PUSH BC Outer loop start: push BC to preserve row count (B) and column count (C) for this row.
set_attr_new_inner_loop 9349 LD (HL),A Inner loop: write attribute byte A to address HL, increment HL, decrement column counter C, repeat until row complete.
934A INC HL
934B DEC C
934C JR NZ,set_attr_new_inner_loop
934E PUSH HL Boundary check: compare HL against screen_attributes_row_16. If HL >= screen_attributes_row_16, exit early via attr_new_exit_early.
934F LD BC,$5A20
9352 OR A
9353 SBC HL,BC
9355 POP HL
9356 JP P,attr_new_exit_early
9359 POP BC Row complete: restore BC, add stride DE to HL, decrement row counter B, repeat outer loop.
935A ADD HL,DE
935B DJNZ set_attr_new_outer_loop
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