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iigs-game-engine
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Fix off-by-one on tile update range and some comment typos

This commit is contained in:
Lucas Scharenbroich 2023-06-27 21:26:17 -05:00
parent a5af4c206c
commit 139a784bfa
1 changed files with 37 additions and 8 deletions
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45
demos/smb/ppu.s
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@ -626,7 +626,7 @@ scanOAMSprites
:loop
lda PPU_OAM,x ; Y-coordinate
cmp #max_nes_y+1 ; Skip anything that is beyond this lint
cmp #max_nes_y+1 ; Skip anything that is beyond this line
bcs :skip
cmp #y_offset
bcc :skip
@ -816,7 +816,7 @@ buildShadowBitmap
; ldy PPU_OAM,x
ldy OAM_COPY,x
cpy #max_nes_y ; Don't increment something right on the edge (allows )
; cpy #max_nes_y ; Don't increment something right on the edge (allows )
; iny ; This is the y-coordinate of the top of the sprite
ldx y2idx,y ; Get the index into the shadowBitmap array for this y coordinate (y -> blk_y)
@ -981,7 +981,6 @@ exposeShadowList
stx :last
cpx shadowListCount
beq :exit
:loop
phx
@ -1037,7 +1036,7 @@ shadowBitmapToList
sep #$30
ldx #y_offset_rows ; Start at he third row (y_offset = 16) walk the bitmap for 25 bytes (200 lines of height)
ldx #y_offset_rows ; Start at the third row (y_offset = 16) walk the bitmap for 25 bytes (200 lines of height)
lda #0
sta shadowListCount ; zero out the shadow list count
@ -1054,7 +1053,7 @@ shadowBitmapToList
:zero_next
inx
cpx #y_height_rows+y_offset_rows+1 ; End at byte 27
cpx #y_height_rows+y_offset_rows ; +1 ; End at byte 27
bcc :zero_loop
bra :exit ; ended while not tracking a sprite, so exit the function
@ -1171,9 +1170,6 @@ drawOAMSprites
pha
jsr scanOAMSprites ; Filter out any sprites that don't need to be drawn
pla
cmpl nmiCount
beq *+4
brk $1F ; Should not have serviced the VBL interrupt here....
cli
jsr buildShadowBitmap ; Run though and quickly create a bitmap of lines with sprites
@ -1356,6 +1352,28 @@ drawTileToScreen
bit #$0100
jne :drawTileToScreenV
; If we compile the sprites, then each word can be implemented as:
;
; x = screen address
;
; ldy #LOOKUP_VAL ; 3 constant 6-bit tile lookup value from NES CHR rom
; lda: 0,x ; 6
; and #MASK ; 3
; ora [USER_FREE_SPACE],y ; 7 lookup and merge in swizzled tile data = *(SwizzlePtr + palbits)
; sta: 0,x ; 6 = 25 cycles / word
;
; Current implementation below is 4+6+6+4+6+7+6 = 39 cycles
;
; Most tiles don't have 4 consecutive transparent pixels, but there will be some minor savings
; by avoiding those operations. For MASK = $FFFF, the simplified code is and solid words are
; quite common, at least 25 - 30% of the words are solid. So conservative estimate of
; 25 * 0.75 + 16 * 0.25 = ~22 cycles/word on average. Throw in the 100% savings from MASK=0
; words and it's close to twice the speed of the current routine.
;
; ldy #LOOKUP_VAL ; 3 constant 6-bit tile lookup value from NES CHR rom
; lda [USER_FREE_SPACE],y ; 7 lookup and merge in swizzled tile data = *(SwizzlePtr + palbits)
; sta: 0,x ; 6 = 16 cycles / word
]line equ 0
lup 8
ldx USER_TILE_ADDR
@ -1558,6 +1576,17 @@ drawTileToScreen
; Assume that when the tile is updated, it includes a full 10-bit value with the
; palette bits included with the lookup bits
;
; If we could compile all of the tiles, then the code becomes
;
; ldy #DATA
; lda [USER_FREE_SPACE],y
; sta: code,x
;
; And we save _at_least_ 11 cycles / word. 6 + 7 + 4 + 4 + 6 = 27 vs 16.
;
; Also, by exposing/short-circuiting the draw_tile stuff to avoid the GTE tile queue, we significantly
; reduce overhead and probably solve the tile column bug.
NESTileBlitter
lda USER_TILE_ID
and #$0600 ; Select the tile palette from the tile id