That old X,Y coordinates generation using that ugly way was a real sh*t.
Now it is ways better (it simply does `random number` modulo `screen rows` - or columns, depends). There also was an error in comparing snakeX,Y with new piece of food's X,Y Now really fixed (I hope, at least, since the bug is terribly difficult to reproduce) Also improved printing routine: now it can print general hexadecimal numbers, and can locate them everywhere across first line (and beyond also, since it is not checked, but if you do, you are a moron). Simply put byte to be print in accumulator, column in Y index, and then jsr.
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61a1c140f4
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104
snake.asm
104
snake.asm
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@ -320,48 +320,69 @@ overEndCheck:
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jsr calcTileMem
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lda (tileMem),y ; read content of head memory location
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cmp foodTile
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bne checkSelfEat ; if memory does not contain food, then skip to self-eat test...
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beq foodEaten ; if memory does contain food, then perform foodEaten actions,
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jmp checkSelfEat ; else just loooong jump to test if I ate myself
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foodEaten:
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ldx length ; else, increment snake length,
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inx
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stx length
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genFood:
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ldx random ; increment random value
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ldx random
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inx
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stx random
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txa
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sta calcTileX ; use it as tile X-coordinate
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lsr ; divide it by 8; maximum expected is 32 (256/8)
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lsr
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lsr
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cmp #18 ; test if it is still > 18
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bcc foodNoMod ; value must be < 18,
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; because it is the highest value v
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; for which v * 40 + 256 < 1000
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; this ensures that piece if food will be placed
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; within visible screen
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sec ; if value is > 18, then subtract 18; now it
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sbc #18 ; surely is less than 18
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foodNoMod:
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cmp #0
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bne foodNoLow ; if it is 0, then set 1 (avoid first line)
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lda #1
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foodNoLow:
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sta calcTileY ; use this new value as tile Y-coordinate
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genFoodX: ; calculate `random` modulo `screenW`
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sec
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sbc screenW
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cmp screenW
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bcs genFoodX
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sta calcTileX
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txa
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genFoodY: ; calculate `random` modulo 22 (22 = screenH - 1)
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sec
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sbc #22
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cmp #22
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bcs genFoodY
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clc ; add 1 because 1st line can not be used
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adc #1
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sta calcTileY
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; Now I have X and Y coordinate for food stored in calcTileX, calcTileY
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; and I must check it is not the location that I am going to overwrite
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; with the head in draw snake head...
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cmp snakeY
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bne foodOK
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lda snakeX
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lda calcTileX
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cmp snakeX
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bne foodOK
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lda calcTileY
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cmp snakeY
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beq genFood
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foodOK:
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; debug -- print choosen X,Y for food
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ldy #$18
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lda calcTileX
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jsr printByte
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ldy #$1b
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lda calcTileY
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jsr printByte
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; debug -- print snake head X,Y
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ldy #$1f
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lda snakeX
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jsr printByte
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ldy #$22
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lda snakeY
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jsr printByte
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ldy #0
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jsr calcTileMem ; calc food address in memory
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lda (tileMem),y ; check if memory is empty
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cmp #$20 ; is there a space?
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bne genFood ; if not, must generate another number
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lda foodTile ; else, just put that fucking piece of food there
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sta (tileMem),y
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lda #$d4
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clc
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adc tileMem + 1
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@ -369,7 +390,9 @@ foodOK:
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lda foodColor
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sta (tileMem),y
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jsr printScore ; print score
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ldy #$10
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lda length
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jsr printByte ; print score
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jmp checkEndSelfEat
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checkEndFood:
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@ -381,6 +404,7 @@ checkSelfEat:
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checkEndSelfEat:
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; Draw snake head
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ldy #0
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lda snakeX ; calc char address in video memory, and put snakeTile
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sta calcTileX
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lda snakeY
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@ -423,6 +447,11 @@ irqalways:
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inx
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stx random
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; debug -- print current random value
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ldy #$14
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lda random
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jsr printByte
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; Go to original system routine
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jmp $ea31
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@ -501,17 +530,11 @@ calcTileEnd: ; now multiplication is ended, so add X
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rts
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; Print score
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printScore:
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; Push registers on stack (save)
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pha
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txa
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pha
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tya
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pha
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; Take length in A and copy also in X
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lda length
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; Print a byte in hexadecimal
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; A input register for byte to print
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; Y input register for printing colum (on first line)
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printByte:
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; Copy parameter also in X
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tax
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lsr ; Take most significant nibble
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@ -519,19 +542,12 @@ printScore:
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lsr
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lsr
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jsr printDigit
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sta $410 ; print msb char at $410
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sta $400,y ; print msb char
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txa ; Take least significant nibble (use previous copy)
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and #$0f
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jsr printDigit
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sta $411 ; print lsb char at $411
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; Pull registers from stack (restore)
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pla
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tay
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pla
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tax
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pla
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sta $401,y ; print lsb char
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rts
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