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Set background color on every frame.

Make some comments more clear.
main
Colin McMillen 7 years ago
parent
commit
1ab6ee37f3
  1. 2
      header.asm
  2. 18
      pewpew.asm

2
header.asm

@ -53,4 +53,6 @@ EmptyHandler:
.ENDS
; Fills unused areas with $00.
; This is the opcode for BRK, which will halt the SNES if executed.
.EMPTYFILL $00

18
pewpew.asm

@ -16,12 +16,7 @@
Start:
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.
; $2100: Screen display register [INIDISP]
;
@ -148,7 +143,7 @@ JoypadY:
bne JoypadDone ; Button not pressed.
lda $21
cmp #0
beq JoypadDone
beq JoypadDone ; Value saturated.
dec $21
JoypadDone:
@ -174,7 +169,7 @@ SetBackgroundColor:
; $20 $21 $22 are (R, G, B), each ranging from [0-31].
; 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.
.rept 5
asl
@ -182,7 +177,7 @@ SetBackgroundColor:
ora $20 ; Red.
sta $2122
; Compute and store the high-order byte.
; Compute the high-order byte and store it in CGDATA.
lda $22 ; Blue.
.rept 2
asl
@ -194,6 +189,11 @@ SetBackgroundColor:
.endr
ora $00
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

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