initial commit

blinking_ball.asm

@@ -0,0 +1,68 @@
+; a blinking ball controllable with WASD
+
+define W 119
+define S 115
+define A 97
+define D 100
+
+jsr init
+
+loop:
+	jsr draw_player
+	jsr clear_player
+	jsr handle_movement
+	jmp loop
+
+init:
+	ldx #0 ; player position
+	stx $1 ; make sure $1 is zeroed
+	lda #1 ; color
+	rts
+
+handle_movement:
+	lda $ff ; load last pressed key
+
+	; reset the last pressed key so that we only move on new input
+	ldy #0
+	sty $ff
+
+	cmp #W
+	beq move_up
+	cmp #S
+	beq move_down
+	cmp #A
+	beq move_left
+	cmp #D
+	beq move_right
+
+	rts
+
+move_up:
+	txa
+	sbc #$20
+	tax
+	rts
+
+move_down:
+	txa
+	adc #$1f
+	tax
+	rts
+
+move_left:
+	dex
+	rts
+
+move_right:
+	inx
+	rts
+
+draw_player:
+	lda #1 ; white
+	sta $0200, X
+	rts
+
+clear_player:
+	lda #0 ; black
+	sta $0200, X
+	rts

colors.asm

@@ -0,0 +1,14 @@
+; A = color to draw
+LDA #0
+
+; X = graphics index
+LDX #0
+
+draw:
+  STA $0200, X ; store A (the color) at $0200 + X
+
+  ADC #1
+
+  CPX #$ff
+  INX
+  BNE draw

mirrored_colors.asm

@@ -0,0 +1,19 @@
+LDA #0 ; color and index
+
+first_draw_pass:
+  TAX
+  STA $0200, X
+  PHA ; push for the second pass
+  ADC #1
+  CMP #$10
+  BNE first_draw_pass
+
+TAX
+DEX
+
+second_draw_pass:
+  PLA
+  INX
+  STA $0200, X
+  CPX #$20
+  BNE second_draw_pass