mirror of
https://github.com/lscharen/iigs-game-engine.git
synced 2025-01-24 13:29:48 +00:00
WIP of fixing horizontal scrolling
This commit is contained in:
Lucas Scharenbroich
parent
50f5da5608
commit
b6fadedfc7
@ -29,6 +29,23 @@ tiledata ENT
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hex 000FF000
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hex 00000000
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hex 00F00F00
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hex 00F00F00
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hex 00F00F00
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hex 00FFFF00
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hex 00000F00
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hex 00000F00
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hex 00000F00
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hex 00000000
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hex 00FFFF00
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hex 00F00000
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hex 00F00000
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hex 00FFF000
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hex 00000F00
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hex 00000F00
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hex 00FFF000
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hex 00000000
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tileend
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@ -39,3 +56,4 @@ tileend
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@ -14,16 +14,16 @@
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; We assume that there is a clean code field in this routine
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SetBG0XPos
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cmp StartX
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beq :out ; Easy, if nothing changed, then nothing changes
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beq :out ; Easy, if nothing changed, then nothing changes
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ldx StartX ; Load the old value (but don't save it yet)
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sta StartX ; Save the new position
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ldx StartX ; Load the old value (but don't save it yet)
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sta StartX ; Save the new position
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lda #DIRTY_BIT_BG0_X
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tsb DirtyBits ; Check if the value is already dirty, if so exit
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bne :out ; without overwriting the original value
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tsb DirtyBits ; Check if the value is already dirty, if so exit
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bne :out ; without overwriting the original value
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stx OldStartX ; First change, so preserve the value
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stx OldStartX ; First change, so preserve the value
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:out rts
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; Simple function that restores the saved opcode that are stached in _applyBG0Xpos. It is
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@ -45,14 +45,14 @@ _RestoreBG0Opcodes
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:exit_offset equ tmp4
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asl
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sta :virt_line_x2 ; Keep track of it
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sta :virt_line_x2 ; Keep track of it
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txa
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asl
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sta :lines_left_x2
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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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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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and #$FFFE
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tax
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@ -61,39 +61,39 @@ _RestoreBG0Opcodes
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:loop
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ldx :virt_line_x2
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ldal BTableLow,x ; Get the address of the first code field line
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ldal BTableLow,x ; Get the address of the first code field line
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tay
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sep #$20
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ldal BTableHigh,x
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pha
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plb ; This is the bank that will receive the updates
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plb ; This is the bank that will receive the updates
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rep #$20
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txa ; lda :virt_line_x2
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txa ; lda :virt_line_x2
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and #$001E
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eor #$FFFF
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inc
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clc
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adc #32
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min :lines_left_x2
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sta :draw_count_x2 ; Do half of this many lines
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sta :draw_count_x2 ; Do half of this many lines
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; y is already set to :base_address
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tax ; :draw_count * 2
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; y is already set to :base_address
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tax ; :draw_count * 2
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tya
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clc
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adc :exit_offset ; Add some offsets to get the base address in the code field line
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adc :exit_offset ; Add some offsets to get the base address in the code field line
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jsr RestoreOpcode
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lda :virt_line_x2 ; advance to the virtual line after the segment we just
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clc ; filled in
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lda :virt_line_x2 ; advance to the virtual line after the segment we just
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clc ; filled in
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adc :draw_count_x2
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sta :virt_line_x2
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lda :lines_left_x2 ; subtract the number of lines we just completed
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lda :lines_left_x2 ; subtract the number of lines we just completed
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sec
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sbc :draw_count_x2
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sta :lines_left_x2
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@ -138,11 +138,13 @@ _ApplyBG0XPos
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:exit_address equ tmp7
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:base_address equ tmp8
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:draw_count_x2 equ tmp9
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:opcode equ tmp0
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:odd_entry_offset equ tmp10
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; This code is fairly succinct. See the corresponding code in Vert.s for more detailed comments.
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lda StartY ; This is the base line of the virtual screen
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sta :virt_line ; Keep track of it
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lda StartY ; This is the base line of the virtual screen
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sta :virt_line ; Keep track of it
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lda ScreenHeight
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sta :lines_left
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@ -185,40 +187,109 @@ _ApplyBG0XPos
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; So, in short, the entry tile position is rounded up from the x-position and the exit
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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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jsr Mod164 ;
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pha ; Save for a bit
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lda StartX ; This is the starting byte offset (0 - 163)
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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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; Now, the left edge of the screen is pushed last, so we need to exit one instruction *after*
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; the location (163 - StartX % 164)
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;
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; x = 0
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;
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; | PEA $0000 |
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; +-----------+
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; | PEA $0000 |
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; +-----------+
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; | JMP loop | <-- Exit here
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; +-----------+
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;
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; x = 1 and 2
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;
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; | PEA $0000 |
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; +-----------+
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; | PEA $0000 | <-- Exit Here
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; +-----------+
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; | JMP loop |
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; +-----------+
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lda #163
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sec
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sbc 1,s
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tay
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; Right now we have the offset of the last visible byte. Add one to get the offset
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; of the byte that will be patched for an exit.
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inc ; (a + 1) % 164
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cmp #164
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bcc :nomod1
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lda #0 ; range check
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:nomod1 and #$FFFE ; clamp and load the BRA for this column
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bcc :hop1
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lda #0
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:hop1
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; If the exit byte is an even value, then this is the spot to exit. If it's an
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; odd value, then round down and use the odd exit path in the blitter to push
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; the high byte of the word.
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bit #$0001
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bne :odd_exit
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; This is the even code path
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tax
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lda CodeFieldEvenBRA,x
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sta :exit_bra
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lda Col2CodeOffset,X
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sta :exit_offset
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bra :do_entry
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; This is the odd code path
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:odd_exit and #$FFFE
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tax
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lda CodeFieldOddBRA,x
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sta :exit_bra
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lda Col2CodeOffset,X
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sta :exit_offset
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tya ; reload (164 - x) % 164
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; Calculate the entry byte into the code field
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:do_entry tya ; reload 163 - 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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sbc ScreenWidth ; back up to entry point
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inc
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bpl :hop2
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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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adc #164
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:hop2
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pla ; Pop off the saved value
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; If the entry index is even, then just go to that column. If it's odd, then we
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; enter the field at the _next_ column and change the entry code to take care of
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; pushing the low byte. In both cases we set the same entry address, but update
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; the blitter opcode at entry_jmp, and for odd entries point, we also need to
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; set the address of odd_entry in the code field
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bit #$0001
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bne :odd_entry
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tax
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lda Col2CodeOffset,x
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sta :entry_offset
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lda #$004C ; set the entry_jmp opcode to JMP
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sta :opcode
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stz :odd_entry_offset ; mark as an even case
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bra :prep_complete
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:odd_entry
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and #$FFFE
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tax
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lda Col2CodeOffset,x
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sta :entry_offset
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lda Col2CodeOffset+2,x
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sta :odd_entry_offset
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lda #$00AF ; set the entry_jmp opcode to LDAL
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sta :opcode
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:prep_complete
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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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@ -228,18 +299,18 @@ _ApplyBG0XPos
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:loop
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lda :virt_line
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asl ; This will clear the carry bit
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asl ; This will clear the carry bit
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tax
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ldal BTableLow,x ; Get the address of the first code field line
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tay ; Save it to use as the base address
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adc :exit_offset ; Add some offsets to get the base address in the code field line
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ldal BTableLow,x ; Get the address of the first code field line
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tay ; Save it to use as the base address
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adc :exit_offset ; Add some offsets to get the base address in the code field line
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sta :exit_address
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sty :base_address
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sep #$20
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ldal BTableHigh,x
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pha
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plb ; This is the bank that will receive the updates
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plb ; This is the bank that will receive the updates
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rep #$20
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lda :virt_line
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@ -250,7 +321,7 @@ _ApplyBG0XPos
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adc #16
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min :lines_left
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sta :draw_count ; Do this many lines
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sta :draw_count ; Do this many lines
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asl
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sta :draw_count_x2
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@ -262,14 +333,14 @@ _ApplyBG0XPos
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; used in odd-aligned cases to determine how to draw the 8-bit value on the left edge of the
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; screen
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; y is already set to :base_address
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tax ; :draw_count_x2
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lda :exit_address ; Save from this location
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; y is already set to :base_address
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tax ; :draw_count_x2
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lda :exit_address ; Save from this location
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jsr SaveOpcode
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ldx :draw_count_x2 ; Do this many lines
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lda :exit_bra ; Copy this value into all of the lines
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ldy :exit_address ; starting at this address
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ldx :draw_count_x2 ; Do this many lines
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lda :exit_bra ; Copy this value into all of the lines
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ldy :exit_address ; starting at this address
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jsr SetConst
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; Next, patch in the CODE_ENTRY value, which is the low byte of a JMP instruction. This is an
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@ -280,17 +351,35 @@ _ApplyBG0XPos
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lda :entry_offset
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ldy :base_address
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jsr SetCodeEntry
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; Now, patch in the opcode
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ldx :draw_count_x2
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lda :opcode
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ldy :base_address
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jsr SetCodeEntryOpcode
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; If this is an odd entry, also set the odd_entry low byte
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lda :odd_entry_offset
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beq :not_odd
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ldx :draw_count_x2
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ldy :base_address
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jsr SetOddCodeEntry
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:not_odd
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rep #$20
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; Do the end of the loop -- update the virtual line counter and reduce the number
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; of lines left to render
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lda :virt_line ; advance to the virtual line after the segment we just
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clc ; filled in
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lda :virt_line ; advance to the virtual line after the segment we just
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clc ; filled in
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adc :draw_count
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sta :virt_line
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lda :lines_left ; subtract the number of lines we just completed
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lda :lines_left ; subtract the number of lines we just completed
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sec
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sbc :draw_count
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sta :lines_left
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@ -497,6 +586,95 @@ SetCodeEntry
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sta: CODE_ENTRY+$0000,y
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:bottom rts
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; SetOddCodeEntry
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;
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; Patch in the low byte at the ODD_ENTRY. Must be called with 8-bit accumulator
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;
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; X = number of lines * 2, 0 to 32
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; Y = starting line * $1000
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; A = address low byte
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SetOddCodeEntry
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jmp (:tbl,x)
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:tbl da :bottom-00,:bottom-03,:bottom-06,:bottom-09
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da :bottom-12,:bottom-15,:bottom-18,:bottom-21
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da :bottom-24,:bottom-27,:bottom-30,:bottom-33
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da :bottom-36,:bottom-39,:bottom-42,:bottom-45
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da :bottom-48
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:top sta ODD_ENTRY+$F000,y
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sta ODD_ENTRY+$E000,y
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sta ODD_ENTRY+$D000,y
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sta ODD_ENTRY+$C000,y
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sta ODD_ENTRY+$B000,y
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sta ODD_ENTRY+$A000,y
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sta ODD_ENTRY+$9000,y
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sta ODD_ENTRY+$8000,y
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sta ODD_ENTRY+$7000,y
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sta ODD_ENTRY+$6000,y
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sta ODD_ENTRY+$5000,y
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sta ODD_ENTRY+$4000,y
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sta ODD_ENTRY+$3000,y
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sta ODD_ENTRY+$2000,y
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sta ODD_ENTRY+$1000,y
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sta: ODD_ENTRY+$0000,y
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:bottom rts
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; SetCodeEntryOpcode
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;
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; Patch in the opcode at the CODE_ENTRY_OPCODE. Must be called with 8-bit accumulator
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;
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; X = number of lines * 2, 0 to 32
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; Y = starting line * $1000
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; A = opcode value
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SetCodeEntryOpcode
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jmp (:tbl,x)
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:tbl da :bottom-00,:bottom-03,:bottom-06,:bottom-09
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da :bottom-12,:bottom-15,:bottom-18,:bottom-21
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da :bottom-24,:bottom-27,:bottom-30,:bottom-33
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da :bottom-36,:bottom-39,:bottom-42,:bottom-45
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da :bottom-48
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:top sta CODE_ENTRY_OPCODE+$F000,y
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sta CODE_ENTRY_OPCODE+$E000,y
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sta CODE_ENTRY_OPCODE+$D000,y
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sta CODE_ENTRY_OPCODE+$C000,y
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sta CODE_ENTRY_OPCODE+$B000,y
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sta CODE_ENTRY_OPCODE+$A000,y
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sta CODE_ENTRY_OPCODE+$9000,y
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sta CODE_ENTRY_OPCODE+$8000,y
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sta CODE_ENTRY_OPCODE+$7000,y
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sta CODE_ENTRY_OPCODE+$6000,y
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sta CODE_ENTRY_OPCODE+$5000,y
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sta CODE_ENTRY_OPCODE+$4000,y
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sta CODE_ENTRY_OPCODE+$3000,y
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sta CODE_ENTRY_OPCODE+$2000,y
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sta CODE_ENTRY_OPCODE+$1000,y
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sta: CODE_ENTRY_OPCODE+$0000,y
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:bottom rts
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@ -20,6 +20,8 @@ Col2CodeOffset lup 82
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dw CODE_TOP+{]step*PER_TILE_SIZE}
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]step equ ]step+1
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--^
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dw CODE_TOP
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; Table of BRA instructions that are used to exit the code field. Separate tables for
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; even and odd aligned cases.
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;
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@ -219,3 +221,5 @@ BTableLow ds 208*2*2
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@ -10,7 +10,9 @@ DP_ENTRY equ entry_1-base
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TWO_LYR_ENTRY equ entry_2-base
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ONE_LYR_ENTRY equ entry_3-base
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CODE_ENTRY_OPCODE equ entry_jmp-base
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CODE_ENTRY equ entry_jmp-base+1 ; low byte of the page-aligned jump address
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ODD_ENTRY equ odd_entry-base+1
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CODE_TOP equ loop-base
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CODE_LEN equ top-base
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CODE_EXIT equ even_exit-base
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@ -791,9 +793,9 @@ long_1 stal *+4-base
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; gets a 1-cycle penalty, but we save 3 cycles here.
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r_is_pea xba ; fast code for PEA
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sep #$30
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sep #$20
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pha
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rep #$30
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rep #$20
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odd_entry jmp $0100 ; unconditionally jump into the "next" instruction in the
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; code field. This is OK, even if the entry point was the
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; last instruction, because there is a JMP at the end of
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@ -973,6 +975,9 @@ top
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