189 lines
3.3 KiB
ArmAsm
189 lines
3.3 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 ; current screen Ypos to draw at
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sty TILEY ; (we draw two at a time as lores
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; is two blocks per byte)
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ldx #0 ; offset in current tilemap
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stx TILEMAP_OFFSET ;
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lda #0 ; init odd/even
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sta TILE_ODD ; (tiles are two rows tall)
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tilemap_outer_loop:
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ldy TILEY ; setup output pointer to current Ypos
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lda gr_offsets,Y ; get address of start of row
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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 ; adjust for page
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sta GBASH
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ldy #0 ; draw row from 0..39
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; might be faster to count backwards
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; but would have to adjust a lot
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tilemap_loop:
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ldx TILEMAP_OFFSET ; get actual tile number
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lda tilemap,X ; from tilemap
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asl ; *4 ; point to tile to draw (4 bytes each)
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asl
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tax
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lda TILE_ODD ; check to see if top or bottom
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beq not_odd_line
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inx ; point to bottom half of tile
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inx
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not_odd_line:
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; draw two blocks
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; note we don't handle transparency in the keen engine
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lda tiles,X
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sta (GBASL),Y ; draw upper right
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iny
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lda tiles+1,X
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sta (GBASL),Y ; draw upper left
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iny
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inc TILEMAP_OFFSET ; point to next tile
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cpy #40 ; until done
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bne tilemap_loop
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; row is done, 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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beq move_to_even_line
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; move ahead to next row
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; for even line we're already pointing to next
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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 #0
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; jmp done_move_to_line
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; reset back to beginning of line to display it again
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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 #TILE_COLS ; subtract off length of row
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sta TILEMAP_OFFSET
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move_to_even_line: ; no need, already points to
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; right place
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done_move_to_line:
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ldy TILEY ; move to next output line
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iny ; each row is two lines
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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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bne tilemap_outer_loop
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rts
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;===================================
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; copy tilemap
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;===================================
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; local tilemap subset is 20x12 tiles = 240 bytes
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; nicely fits in one page
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;
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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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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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done_tilemap_subset:
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; activate yorps
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ldx #0
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clc
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lda TILEMAP_X
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adc #22
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sta INL
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activate_yorp_loop:
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; if TILEMAP_X+22>YORP_X
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lda INL
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cmp enemy_data_tilex,X
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bcc next_yorp
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lda #1
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sta enemy_data_out,X
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next_yorp:
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inx
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cpx #NUM_ENEMIES
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bne activate_yorp_loop
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rts
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