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https://github.com/lscharen/iigs-game-engine.git
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WIP on BG0X positioning; fix tile horizonal calculation
This commit is contained in:
Lucas Scharenbroich
parent
be446589b0
commit
50f5da5608
@ -42,7 +42,7 @@ SHR_PALETTES equ $E19E00
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tiledata ext
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; Feature flags
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NO_INTERRUPTS equ 0 ; turn off for crossrunner debugging
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NO_INTERRUPTS equ 1 ; turn off for crossrunner debugging
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; Typical init
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@ -289,6 +289,8 @@ DoTiles
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:rowloop
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lda #0
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sta :column,s
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lda #$0010
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sta :tile,s
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:colloop
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lda :row,s
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@ -300,7 +302,6 @@ DoTiles
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lda :tile,s
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inc
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and #$000F
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sta :tile,s
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lda :column,s
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@ -322,6 +323,8 @@ DoTiles
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; Set up the code field and render it
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DoFrame
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lda #$FFFF
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sta DirtyBits
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jsr Render ; Render the play field
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rts
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@ -737,6 +740,10 @@ qtRec adrl $0000
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@ -1,7 +1,40 @@
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REL
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DSK TILESEG
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tiledata ENT
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ds 65536
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hex 0000F000
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hex 000FF000
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hex 0000F000
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hex 0000F000
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hex 0000F000
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hex 0000F000
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hex 000FFF00
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hex 00000000
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hex 000FF000
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hex 00F00F00
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hex 00000F00
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hex 0000F000
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hex 000F0000
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hex 00F00000
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hex 00FFFF00
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hex 00000000
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hex 000FF000
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hex 00F00F00
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hex 00000F00
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hex 0000F000
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hex 00000F00
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hex 00F00F00
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hex 000FF000
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hex 00000000
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tileend
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@ -109,6 +109,24 @@ _RestoreBG0Opcodes
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; routine. The reason is that the restore *must* be applied using the (StartX, StartY)
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; values from the previous frame, which requires logic that is not relevant to setting
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; up the code field.
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;
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; This function is where the reverse-mapping aspect of the code field is compensated
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; for. In the initialize case where X = 0, the exit point is at the *end* of
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; the code buffer line
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;
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; +----+----+ ... +----+----+----+
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; | 82 | 80 | | 04 | 02 | 00 |
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; +----+----+ ... +----+----+----+
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; ^ x=0
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;
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; As the screen scrolls right-to-left, the exit position moves to earlier memory
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; locations until wrapping around from 163 to 0.
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;
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; The net calculation are
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;
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; x_exit = (164 - x) % 164
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; x_enter = (164 - x - width) % 164
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;
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_ApplyBG0XPos
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:virt_line equ tmp1
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@ -168,31 +186,39 @@ _ApplyBG0XPos
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; tile position is rounded down.
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lda StartX ; This is the starting byte offset (0 - 163)
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inc ; round up to calculate the entry column
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and #$FFFE
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jsr Mod164 ;
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pha ; Save for a bit
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lda #164 ; The left edge of the screen is the exit point
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sec ; of the blitter. So calculate that location for
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sbc 1,s ; the "starting" point of the render
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tay ; cache this value
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cmp #164
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bcc :nomod1
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lda #0 ; range check
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:nomod1 and #$FFFE ; clamp and load the BRA for this column
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tax
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lda CodeFieldOddBRA,x
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sta :exit_bra
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lda Col2CodeOffset,X
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sta :exit_offset
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tya ; reload (164 - x) % 164
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sec
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sbc ScreenWidth ; back up to entry point, which corresponds to the
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bpl :nomod2 ; right edge
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clc
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adc #184
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:nomod2 inc ; round up to calculate the entry column
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cmp #184
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bcc :nomod3
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lda #0
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:nomod3 and #$FFFE
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tax
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lda Col2CodeOffset,X ; This is an offset from the base page boundary
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sta :entry_offset
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lda StartX ; Repeat with adding the screen width
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clc ; to calculate the exit column
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adc ScreenWidth
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bit #$0001 ; Check if odd or even
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bne :isOdd
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and #$FFFE
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tax
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lda CodeFieldEvenBRA,x
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sta :exit_bra
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bra :wasEven
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:isOdd
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and #$FFFE
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tax
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lda CodeFieldOddBRA,x
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sta :exit_bra
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:wasEven
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lda Col2CodeOffset,X
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sta :exit_offset
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pla ; Pop off the saved value
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; Main loop that
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;
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@ -520,6 +546,21 @@ SetCodeEntry
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@ -13,9 +13,6 @@
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; lda #DATA
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; ldx Col2CodeOffset,y
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; sta $0001,x
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;
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; This table is necessary, because due to the data being drawn via stack instructions, the
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; tile order is reversed.
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PER_TILE_SIZE equ 3
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]step equ 0
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@ -221,3 +218,4 @@ BTableLow ds 208*2*2
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@ -313,6 +313,46 @@ SetYPos sta StartY ; Save the position
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plb
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rts
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; Special subroutine to divide the accumulator by 164 and return remainder in the Accumulator
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;
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; 164 = $A4 = 1010_0100
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Mod164 cmp #%1010010000000000
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bcc *+5
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sbc #%1010010000000000
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cmp #%0101001000000000
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bcc *+5
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sbc #%0101001000000000
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cmp #%0010100100000000
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bcc *+5
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sbc #%0010100100000000
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cmp #%0001010010000000
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bcc *+5
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sbc #%0001010010000000
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cmp #%0000101001000000
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bcc *+5
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sbc #%0000101001000000
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cmp #%0000010100100000
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bcc *+5
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sbc #%0000010100100000
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cmp #%0000001010010000
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bcc *+5
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sbc #%0000001010010000
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cmp #%0000000101001000
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bcc *+5
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sbc #%0000000101001000
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cmp #%0000000010100100
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bcc *+5
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sbc #%0000000010100100
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rts
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; Special subroutine to divide the accumulator by 208 and return remainder in the Accumulator
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;
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; 208 = $D0 = 1101_0000
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@ -930,6 +970,9 @@ top
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@ -13,8 +13,8 @@
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; A low-level function that copies 8x8 tiles directly into the code field space.
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;
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; A = Tile ID (0 - 1023)
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; X = Tile row (0 - 25)
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; Y = Tile columns (0 - 40)
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; X = Tile column (0 - 40)
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; Y = Tile row (0 - 25)
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CopyTile
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phb ; save the current bank
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pha ; save the tile ID
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@ -31,8 +31,13 @@ CopyTile
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pha ; save for a few instruction
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rep #$20
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txa ; there are two columns per tile, so multiple by 4
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asl
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phx ; Reverse the tile index since x = 0 is at the end
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lda #40
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sec
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sbc 1,s
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plx
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asl ; there are two columns per tile, so multiple by 4
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asl ; asl will clear the carry bit
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tax
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lda Col2CodeOffset,x
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@ -88,45 +93,48 @@ CopyTileConst sta: $0000,y
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sta $7003,y
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rts
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:CopyTileMem asl
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:CopyTileMem sec
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sbc #$0010
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asl
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asl
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asl
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asl
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asl
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tax
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CopyTileLinear ldal tiledata+0,x
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sta: $0000,y
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ldal tiledata+2,x
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CopyTileLinear ldal tiledata+0,x ; The low word goes in the *next* instruction
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sta: $0003,y
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ldal tiledata+2,x
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sta: $0000,y
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ldal tiledata+4,x
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sta $1000,y
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ldal tiledata+6,x
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sta $1003,y
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ldal tiledata+6,x
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sta $1000,y
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ldal tiledata+8,x
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sta $2000,y
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ldal tiledata+10,x
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sta $2003,y
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ldal tiledata+10,x
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sta $2000,y
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ldal tiledata+12,x
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sta $3000,y
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ldal tiledata+14,x
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sta $3003,y
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ldal tiledata+14,x
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sta $3000,y
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ldal tiledata+16,x
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sta $4000,y
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ldal tiledata+18,x
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sta $4003,y
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ldal tiledata+18,x
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sta $4000,y
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ldal tiledata+20,x
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sta $5000,y
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ldal tiledata+22,x
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sta $5003,y
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ldal tiledata+22,x
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sta $5000,y
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ldal tiledata+24,x
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sta $6000,y
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ldal tiledata+26,x
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sta $6003,y
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ldal tiledata+26,x
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sta $6000,y
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ldal tiledata+28,x
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sta $7000,y
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ldal tiledata+30,x
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sta $7003,y
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ldal tiledata+30,x
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sta $7000,y
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rts
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@ -143,6 +151,11 @@ CopyTileLinear ldal tiledata+0,x
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