Visual Juice

What Is “Juice”?

Game designers use “juice” to describe the small visual and audio effects that make games feel satisfying. A button press that does nothing visible feels unresponsive. The same button press with a screen flash, sound effect, and particle burst feels powerful.

We already have audio feedback. Now we add visual punch.

The Border Register

The C64’s border colour lives at $D020. Changing this single byte transforms the entire screen surround:

; Border colour register
; Writing here instantly changes the border
; Values 0-15 map to the C64 colour palette
            lda #$02        ; Red
            sta $d020       ; Border turns red immediately

We’ll flash the border on key moments: cyan when the multiplier increases, red when the player misses.

Effect Timers

Each visual effect needs a timer. When triggered, we set the timer. Each frame, we decrement it. When it hits zero, the effect ends:

; Visual juice constants
BORDER_FLASH_TIME = 8       ; Frames for border flash
HIT_PULSE_TIME    = 3       ; Frames for hit zone pulse
MISS_FLASH_TIME   = 4       ; Frames for miss screen flash

; Visual juice variables
border_flash_timer: !byte $00   ; Frames remaining for border flash
hit_pulse_timer:    !byte $00   ; Frames remaining for hit pulse
miss_flash_timer:   !byte $00   ; Frames remaining for miss flash

At 50 frames per second on PAL, 8 frames gives us roughly 160ms of flash — noticeable but not distracting.

Triggering Effects

When the multiplier increases, we want celebration. Add the border flash trigger to the combo routine:

update_combo:
            ; Trigger hit pulse effect
            lda #HIT_PULSE_TIME
            sta hit_pulse_timer

            inc combo_count
            lda combo_count
            cmp #COMBO_THRESHOLD
            bcc uc_done

            lda multiplier
            cmp #MAX_MULTIPLIER
            bcs uc_reset
            inc multiplier

            ; Trigger border flash on multiplier increase
            lda #BORDER_FLASH_TIME
            sta border_flash_timer

uc_reset:
            lda #$00
            sta combo_count
uc_done:
            rts

Every hit triggers the pulse. But the border flash only fires when the multiplier actually increases — making it feel special.

Miss Feedback

Missing should feel bad. A red border flash reinforces the mistake:

update_crowd_miss:
            jsr play_bum_note

            ; Trigger miss flash effect
            lda #MISS_FLASH_TIME
            sta miss_flash_timer

            ; Reset combo and multiplier
            lda #$00
            sta combo_count
            lda #$01
            sta multiplier
            ; ...

The miss flash is shorter than the multiplier flash. We want the player to notice, not to punish them with a long red screen.

The Update Routine

Each frame, we check all effect timers and set the border colour accordingly:

update_visual_effects:
            ; Border flash (cyan when multiplier increases)
            lda border_flash_timer
            beq uve_no_border
            dec border_flash_timer
            lda #COL_CYAN           ; Bright cyan border flash
            sta $d020
            jmp uve_hit_pulse

uve_no_border:
            ; Miss flash overrides normal
            lda miss_flash_timer
            beq uve_normal_border
            dec miss_flash_timer
            lda #COL_RED            ; Red border on miss
            sta $d020
            jmp uve_hit_pulse

uve_normal_border:
            lda #$00                ; Black border normally
            sta $d020

uve_hit_pulse:
            ; Hit pulse - brighten hit zones briefly
            lda hit_pulse_timer
            beq uve_done
            dec hit_pulse_timer
uve_done:
            rts

The priority matters: multiplier flash beats miss flash beats normal. If somehow both trigger simultaneously, the positive feedback wins.

Integration

Add the update call to the game loop, after other updates:

            ; Update grade text (Unit 10)
            jsr update_grade_text

            ; Update visual effects (Unit 12)
            jsr update_visual_effects

            ; Update displays
            jsr update_display
            jsr draw_crowd

Initialisation

Reset all effect timers when starting a new game:

            ; Reset visual effects
            lda #$00
            sta border_flash_timer
            sta hit_pulse_timer
            sta miss_flash_timer

The Feel Factor

These effects are subtle. You might not consciously notice them. But play the game with and without them — the difference is dramatic.

Good juice follows a principle: reward success loudly, punish failure quietly. The cyan multiplier flash is longer and brighter than the red miss flash. Players feel celebrated for achievement without feeling beaten down by mistakes.

Beyond the Border

The C64 offers more juice possibilities:

• Colour cycling: Rapidly changing character colours
• Screen shake: Offsetting the screen position briefly
• Sprite overlays: Temporary graphics for explosions
• Raster effects: Mid-screen colour changes

Each adds complexity. For SID Symphony, border flashes deliver maximum impact with minimum code.

What’s Next

The game now looks and sounds polished. In Unit 13, we add difficulty progression — making the song speed up as the player succeeds, keeping the challenge fresh.