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Add proper handling of wraparound in vertical positioning

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This commit is contained in:
Lucas Scharenbroich 2021-07-17 21:00:46 -05:00
parent 4b390fef20
commit 160a9afafb
7 changed files with 76 additions and 19 deletions
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7
src/Actions.s
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@ -27,9 +27,9 @@ MoveRight
pla
rts
MoveDown
MoveUp
clc
adc StartY ; Increment the virtual X-position
adc StartY ; Increment the virtual Y-position
jsr SetBG0YPos
lda StartY
@ -39,7 +39,7 @@ MoveDown
jsr DoFrame
rts
MoveUp
MoveDown
pha
lda StartY
sec
@ -104,3 +104,4 @@ FPSStr str 'FPS'

7
src/App.Main.s
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@ -643,10 +643,16 @@ BlitInit
stz ScreenTileHeight
stz ScreenTileWidth
stz StartX
stz StartXMod164
stz StartY
stz StartYMod208
stz EngineMode
stz DirtyBits
stz LastPatchOffset
stz BG1StartX
stz BG1StartXMod164
stz BG1StartY
stz BG1StartYMod208
]step equ 0
lup 13
@ -976,5 +982,6 @@ qtRec adrl $0000

9
src/Render.s
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@ -64,10 +64,13 @@ Render
jsr ShadowOff
jsr ShadowOn
jsr _ApplyBG0XPos ; Patch the PEA instructions with exit BRA opcode
; It's important to do _ApplyBG0YPos first because it calculates the value of StartY % 208 which is
; used in all of the other loops
jsr _ApplyBG0YPos ; Set stack addresses for the virtual lines to the physical screen
jsr _ApplyBG0XPos ; Patch the PEA instructions with exit BRA opcode
jsr _ApplyBG1YPos ; Adjust the index values into the BG1 bank buffer
jsr _ApplyBG1XPos ; Adjust the direct page pointers to the BG1 bank
jsr _ApplyBG1YPos
ldx #0 ; Blit the full virtual buffer to the screen
ldy ScreenHeight
@ -90,3 +93,5 @@ Render

46
src/blitter/BG1.s
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@ -1,16 +1,38 @@
; Initialization and setup routines for the second background
_InitBG1
jsr _ApplyBG1XPos
jsr _ApplyBG1YPos
jsr _ApplyBG1XPos
rts
SetBG1XPos
sta BG1StartX
rts
cmp BG1StartX
beq :out ; Easy, if nothing changed, then nothing changes
ldx BG1StartX ; Load the old value (but don't save it yet)
sta BG1StartX ; Save the new position
lda #DIRTY_BIT_BG1_X
tsb DirtyBits ; Check if the value is already dirty, if so exit
bne :out ; without overwriting the original value
stx OldBG1StartX ; First change, so preserve the value
:out rts
SetBG1YPos
sta BG1StartY
rts
cmp BG1StartY
beq :out ; Easy, if nothing changed, then nothing changes
ldx BG1StartY ; Load the old value (but don't save it yet)
sta BG1StartY ; Save the new position
lda #DIRTY_BIT_BG1_Y
tsb DirtyBits ; Check if the value is already dirty, if so exit
bne :out ; without overwriting the original value
stx OldBG1StartY ; First change, so preserve the value
:out rts
; Everytime either BG1 or BG0 X-position changes, we have to update the direct page values. We
; *could* do this by adjusting the since address offset, but we have to change up to 200 values
@ -86,9 +108,12 @@ _ApplyBG1YPos
:draw_count equ tmp2
:ytbl_idx equ tmp3
stz :ytbl_idx ; Start copying from the first entry in the table
lda BG1StartY
jsr Mod208
sta BG1StartYMod208
sta :ytbl_idx ; Start copying from the first entry in the table
lda StartY ; This is the base line of the virtual screen
lda StartYMod208 ; This is the base line of the virtual screen
sta :virt_line ; Keep track of it
lda ScreenHeight
@ -246,6 +271,13 @@ CopyBG1YTableToBG1Addr

16
src/blitter/DirectPage.s
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@ -24,12 +24,16 @@ OldStartY equ 32
LastPatchOffset equ 34 ; Offset into code field that was patched with BRA instructions
StartXMod164 equ 36
StartYMod208 equ 38
BG1StartX equ 38 ; Logical offset of the second background
BG1StartXMod164 equ 40
BG1StartX equ 40 ; Logical offset of the second background
BG1StartXMod164 equ 42
BG1StartY equ 42
BG1StartYMod208 equ 44
BG1StartY equ 44
BG1StartYMod208 equ 46
OldBG1StartX equ 48
OldBG1StartY equ 50
bstk equ 208 ; 16-byte stack to push bank addresses
@ -66,6 +70,10 @@ DIRTY_BIT_BG1_Y equ $0008

3
src/blitter/Horz.s
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@ -146,7 +146,7 @@ _ApplyBG0XPos
; This code is fairly succinct. See the corresponding code in Vert.s for more detailed comments.
:ok
lda StartY ; This is the base line of the virtual screen
lda StartYMod208 ; This is the base line of the virtual screen
sta :virt_line ; Keep track of it
lda ScreenHeight
@ -745,3 +745,4 @@ SetCodeEntryOpcode

7
src/blitter/Vert.s
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@ -5,8 +5,7 @@
; SetBG0YPos
;
; Set the virtual position of the primary background layer. In addition to
; updating the direct page state locations, this routine needs to
; Set the virtual position of the primary background layer.
SetBG0YPos
cmp StartY
beq :out ; Easy, if nothing changed, then nothing changes
@ -38,6 +37,9 @@ _ApplyBG0YPos
stz :rtbl_idx ; Start copying from the first entry in the table
lda StartY ; This is the base line of the virtual screen
jsr Mod208
sta StartYMod208
sta :virt_line ; Keep track of it
; copy a range of address from the table into the destination bank. If we restrict ourselves to
@ -188,3 +190,4 @@ CopyRTableToStkAddr
sta: STK_ADDR+$0000,y
:none rts