163 lines
2.7 KiB
ArmAsm
163 lines
2.7 KiB
ArmAsm
;================================
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; draw local tilemap to screen
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;================================
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; tilemap is 20x12 grid with 2x4 (well, 2x2) tiles
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draw_tilemap:
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ldy #0 ; Y on screen currently drawing
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sty tiley ; we draw two at a time
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ldx #1 ; offset in current screen
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stx tilemap_offset ; tilemap
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lda #0 ; init odd/even
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sta tile_odd
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tilemap_outer_loop:
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ldy tiley ; setup output pointer to current Y
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lda gr_offsets,Y
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sta GBASL
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lda gr_offsets+1,Y
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clc
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adc DRAW_PAGE
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sta GBASH
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ldy #0
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; ldy #6 ; we draw in window 6->34
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tilemap_loop:
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ldx tilemap_offset ; get actual tile
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lda tilemap,X
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asl ; *4 ; get offset in tile
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asl
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tax
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lda tile_odd
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beq not_odd_line
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inx
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inx
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not_odd_line:
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lda tiles,X ; draw two tiles
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cmp #$AA ; transparency
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beq skip_tile1
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sta (GBASL),Y
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skip_tile1:
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iny
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lda tiles+1,X
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cmp #$AA
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beq skip_tile2
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sta (GBASL),Y
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skip_tile2:
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iny
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inc tilemap_offset
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cpy #40 ; until done
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; cpy #34 ; until done
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bne tilemap_loop
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; move to next line
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lda tile_odd ; toggle odd/even
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eor #$1 ; (should we just add/mask?)
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sta tile_odd
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bne move_to_odd_line
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; ????
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move_to_even_line:
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lda tilemap_offset
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clc
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adc #2
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jmp done_move_to_line
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move_to_odd_line:
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lda tilemap_offset
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sec
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sbc #14
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done_move_to_line:
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sta tilemap_offset
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ldy tiley ; move to next output line
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iny
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iny
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sty tiley
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cpy #48 ; check if at end
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; cpy #40 ; check if at end
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bne tilemap_outer_loop
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rts
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; these should probably be in the zero page
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tilemap_offset: .byte $00
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tile_odd: .byte $00
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tiley: .byte $00
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;===================================
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; copy tilemap
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;===================================
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; want to copy a 16x10 area from global tileset to local
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; originally 16x10 16x10 = 160 bytes
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; extend to 20x12 for full screen? 20x12 = 240 bytes
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; big tilemap is 256*40
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; so each row is a page
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; TILEMAP_X, TILEMAP_Y specify where in big
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; copy to tilemap
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TILEMAP_X_COPY_SIZE = 20
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TILEMAP_Y_COPY_SIZE = 12
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copy_tilemap_subset:
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; set start
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lda TILEMAP_Y
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clc ; set start
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adc #>big_tilemap ; each row is a page, so adding
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; Y to top byte is indexing to row
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sta cptl1_smc+2 ; set proper row in big tilemap
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adc #TILEMAP_Y_COPY_SIZE
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sta cptl3_smc+1 ; set loop limit (end)
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; reset row
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lda #<tilemap
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sta cptl2_smc+1 ; set small tilemap to row0
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cp_tilemap_outer_loop:
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ldx TILEMAP_X
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ldy #0
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cp_tilemap_inner_loop:
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cptl1_smc:
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lda $9400,X
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cptl2_smc:
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sta $BC00,Y
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iny
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inx
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cpy #TILEMAP_X_COPY_SIZE
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bne cp_tilemap_inner_loop
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; next line
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inc cptl1_smc+2 ; incremement page
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clc
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lda cptl2_smc+1 ; increment row
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adc #TILEMAP_X_COPY_SIZE
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sta cptl2_smc+1
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lda cptl1_smc+2
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cptl3_smc:
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cmp #TILEMAP_Y_COPY_SIZE
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bne cp_tilemap_outer_loop
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rts
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