diff options
Diffstat (limited to 'snake.s')
| -rw-r--r-- | snake.s | 77 |
1 files changed, 76 insertions, 1 deletions
@@ -17,6 +17,11 @@ BANKS 1 .enum $0000 buttons_pressed DB +head_x DB +head_y DB +direction DB ; 0: up, 1: down, 2: left, 3: right +frame_skip DB +frame_count DB .ende @@ -73,6 +78,13 @@ LoadPalettesLoop: ; initialize variables in ram LDA #$00 STA buttons_pressed + STA direction + STA frame_count + LDA #$80 + STA head_x + STA head_y + LDA #30 + STA frame_skip LDA #%00010000 ; enable sprites STA $2001 @@ -115,24 +127,87 @@ handle_up: AND #%00001000 CMP #$00 BEQ handle_down + LDA #$00 + STA direction handle_down: LDA buttons_pressed AND #%00000100 CMP #$00 BEQ handle_left + LDA #$01 + STA direction handle_left: LDA buttons_pressed AND #%00000010 CMP #$00 BEQ handle_right + LDA #$02 + STA direction handle_right: LDA buttons_pressed AND #%00000001 CMP #$00 - BEQ nmi_return + BEQ handle_frame + LDA #$03 + STA direction + +handle_frame: + LDX frame_count + INX + STX frame_count + CPX frame_skip + BMI draw_snake + + LDA #$00 + STA frame_count + + LDA #$00 + CMP direction + BEQ go_up + LDA #$01 + CMP direction + BEQ go_down + LDA #$02 + CMP direction + BEQ go_left + +go_right: + LDA head_x + ADC #$08 + STA head_x + JMP draw_snake +go_up: + LDA head_y + SBC #$08 + STA head_y + JMP draw_snake +go_down: + LDA head_y + ADC #$08 + STA head_y + JMP draw_snake +go_left: + LDA head_x + SBC #$08 + STA head_x + +draw_snake: + LDA head_y + STA $0200 + LDA #$00 + STA $0201 + LDA #$00 + STA $0202 + LDA head_x + STA $0203 + + LDA #$00 + STA $2003 + LDA #$02 + STA $4014 nmi_return: RTI |