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Conscious use of assembler pre-processor directives, to avoid use of magic numbers and memory locations for costants

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giomba 2017-12-27 18:26:44 +01:00
parent e177fdcd86
commit 3ce810a482
1 changed files with 32 additions and 35 deletions
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67
snake.asm
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@ -15,13 +15,6 @@ printIntroString = $a3
; Pointer to screen position where to print intro string ($fb-$fc)
introScreenStart = $fb
; Status of the game (costants pre-processor defined)
ST_INTRO0 = 0
ST_INTRO1 = 1
ST_PLAY = 2
ST_OUTRO = 3
ST_END = 4
org $801
. = $801 ; 10 SYS9216 ($2400) BASIC autostart
BYTE #$0b,#$08,#$0a,#$00,#$9e,#$39,#$32,#$31,#$36,#$00,#$00,#$00
@ -89,20 +82,24 @@ outroDelay
; Costants
; ----------------------------------------------------------------------
; Screen width and height
screenW:
BYTE #40
screenH:
BYTE #24
snakeTile:
BYTE #81
snakeColor:
BYTE #5
foodTile:
BYTE #90
foodColor:
BYTE #15
; Status of the game (costants pre-processor defined, sort of enum)
ST_INTRO0 = 0
ST_INTRO1 = 1
ST_PLAY = 2
ST_OUTRO = 3
ST_END = 4
; Screen features
SCREEN_W = 40
SCREEN_H = 24
; Snake features
SNAKE_TILE = 81
SNAKE_COLOR = 5
; Food features
FOOD_TILE = 90
FOOD_COLOR = 15
; Strings
gameoverString:
BYTE "GAME IS OVER"
BYTE #0
@ -240,7 +237,7 @@ upperbarLoop:
bne upperbarLoop
; Init game variables
lda foodTile
lda #FOOD_TILE
sta $500 ; Put first piece of food
lda #4
sta irqn ; Initialize interrupt divider
@ -595,7 +592,7 @@ overEndCheck:
sta calcTileY
jsr calcTileMem
lda (tileMem),y ; read content of head memory location
cmp foodTile
cmp #FOOD_TILE
beq foodEaten ; if memory does contain food, then perform foodEaten actions,
jmp checkSelfEat ; else just loooong jump to test if I ate myself
foodEaten:
@ -608,15 +605,15 @@ genFood:
stx random
txa
genFoodX: ; calculate `random` modulo `screenW`
genFoodX: ; calculate `random` modulo SCREEN_W
sec
sbc screenW
cmp screenW
sbc #SCREEN_W
cmp #SCREEN_W
bcs genFoodX
sta calcTileX
txa
genFoodY: ; calculate `random` modulo 22 (22 = screenH - 1)
genFoodY: ; calculate `random` modulo 22 (22 = SCREEN_H - 1)
sec
sbc #22
cmp #22
@ -648,14 +645,14 @@ foodOK:
lda (tileMem),y ; check if memory is empty
cmp #$20 ; is there a space?
bne genFood ; if not, must generate another number
lda foodTile ; else, just put that fucking piece of food there
lda #FOOD_TILE ; else, just put that fucking piece of food there
sta (tileMem),y
lda #$d4
clc
adc tileMem + 1
sta tileMem + 1
lda foodColor
lda #FOOD_COLOR
sta (tileMem),y
; print score at $10th column
@ -668,26 +665,26 @@ checkEndFood:
; --- Self eat ---
checkSelfEat:
cmp snakeTile
cmp #SNAKE_TILE
bne checkEndSelfEat
jmp gameover
checkEndSelfEat:
; Draw snake head
ldy #0
lda snakeX ; calc char address in video memory, and put snakeTile
lda snakeX ; calc char address in video memory, and put SNAKE_TILE
sta calcTileX
lda snakeY
sta calcTileY
jsr calcTileMem
lda snakeTile
lda #SNAKE_TILE
sta (tileMem),y
lda #$d4 ; add #$d400 to previous address (obtain color memory
clc ; correspondent), and put snakeColor
clc ; correspondent), and put SNAKE_COLOR
adc tileMem + 1
sta tileMem + 1
lda snakeColor
lda #SNAKE_COLOR
sta (tileMem),y
; Erase snake tail
@ -743,7 +740,7 @@ statusOutroEnd:
; ----------------------------------------------------------------------
; Do some math to calculate tile address in video memory
; using x,y coordinates
; Formula: addr = $400 + y * screenW + x
; Formula: addr = $400 + y * SCREEN_W + x
calcTileMem:
; Save registers
pha
@ -764,7 +761,7 @@ calcTileMult:
beq calcTileEnd ; if Y is equal to zero, nothing to do, just skip moltiplication, else...
dey ; decrement Y
clc
lda screenW ; A = screen width = 40
lda #SCREEN_W ; A = screen width = 40
adc tileMem ; A = screen width + tileMem (low)
sta tileMem ; update tileMem (low)
lda #0 ; do the same with higher byte: A = 0