mcmillen/pewpew
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Set background color on every frame.

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Make some comments more clear.
This commit is contained in:
Colin McMillen 2015-05-22 15:09:14 -04:00
parent f6ef82180d
commit 1ab6ee37f3
2 changed files with 11 additions and 9 deletions
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2
header.asm
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@ -53,4 +53,6 @@ EmptyHandler:
.ENDS .ENDS
; Fills unused areas with $00.
; This is the opcode for BRK, which will halt the SNES if executed.
.EMPTYFILL $00 .EMPTYFILL $00

18
pewpew.asm
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@ -16,12 +16,7 @@
Start: Start:
InitSNES ; Initialize SNES. InitSNES ; Initialize SNES.
; Set the background color.
; $2121 is the color palette selection register [CGADD].
; Storing 0 because that's the SNES background color.
stz $2121
; Turn on the screen. ; Turn on the screen.
; $2100: Screen display register [INIDISP] ; $2100: Screen display register [INIDISP]
; ;
@ -148,7 +143,7 @@ JoypadY:
bne JoypadDone ; Button not pressed. bne JoypadDone ; Button not pressed.
lda $21 lda $21
cmp #0 cmp #0
beq JoypadDone beq JoypadDone ; Value saturated.
dec $21 dec $21
JoypadDone: JoypadDone:
@ -174,7 +169,7 @@ SetBackgroundColor:
; $20 $21 $22 are (R, G, B), each ranging from [0-31]. ; $20 $21 $22 are (R, G, B), each ranging from [0-31].
; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr] ; The palette color format is 15-bit: [0bbbbbgg][gggrrrrr]
; Compute and store the low-order byte. ; Compute and the low-order byte and store it in CGDATA.
lda $21 ; Green. lda $21 ; Green.
.rept 5 .rept 5
asl asl
@ -182,7 +177,7 @@ SetBackgroundColor:
ora $20 ; Red. ora $20 ; Red.
sta $2122 sta $2122
; Compute and store the high-order byte. ; Compute the high-order byte and store it in CGDATA.
lda $22 ; Blue. lda $22 ; Blue.
.rept 2 .rept 2
asl asl
@ -194,6 +189,11 @@ SetBackgroundColor:
.endr .endr
ora $00 ora $00
sta $2122 sta $2122
; Set the background color.
; $2121 is the color palette selection register [CGADD].
; Entry 0 corresponds to the SNES background color.
stz $2121
rts rts