A C64 Game - Step 86

And something different for a change: Added road side stones to the story pages to make it look a bit neater.

Looks better in motion :)



It's actually pretty simple: We add a stone in front and one in the back. Store positions and update them every frame with different deltas.

Start with the position value variables:

MOVE_STONES
          !byte 0

MOVE_STONE_POS_BACK
          !byte 0

MOVE_STONE_POS_FRONT
          !byte 0

...and the actual code.

STONE_BACK_DISTANCE = 20
STONE_FRONT_DISTANCE = 24
          lda MOVE_STONES
          bne +
          jmp .NoStones

+

          ;background
          ldy #19
          lda SCREEN_LINE_OFFSET_TABLE_LO,y
          sta ZEROPAGE_POINTER_1
          sta ZEROPAGE_POINTER_2
          lda SCREEN_LINE_OFFSET_TABLE_HI,y
          sta ZEROPAGE_POINTER_1 + 1
          clc
          adc #( ( SCREEN_COLOR - SCREEN_CHAR ) >> 8 )
          sta ZEROPAGE_POINTER_2 + 1
          ldy MOVE_STONE_POS_BACK

-
          lda #32
          sta (ZEROPAGE_POINTER_1),y
          tya
          clc
          adc #STONE_BACK_DISTANCE
          tay
          cpy #39
          bcc -

          lda MOVE_STONE_POS_BACK
          clc
          adc #1

-
          cmp #STONE_BACK_DISTANCE
          bcc +
          sec
          sbc #STONE_BACK_DISTANCE
          jmp -

+
          sta MOVE_STONE_POS_BACK
          ldy MOVE_STONE_POS_BACK

-
          lda #149
          sta (ZEROPAGE_POINTER_1),y
          lda #8
          sta (ZEROPAGE_POINTER_2),y
          tya
          clc
          adc #STONE_BACK_DISTANCE
          tay
          cpy
          #39
          bcc -

          ;foreground
          ldy #22
          lda SCREEN_LINE_OFFSET_TABLE_LO,y
          sta ZEROPAGE_POINTER_1
          sta ZEROPAGE_POINTER_2
          lda SCREEN_LINE_OFFSET_TABLE_HI,y
          sta ZEROPAGE_POINTER_1 + 1
          clc
          adc #( ( SCREEN_COLOR - SCREEN_CHAR ) >> 8 )
          sta ZEROPAGE_POINTER_2 + 1

          ldy MOVE_STONE_POS_FRONT

-
          lda #32
          sta (ZEROPAGE_POINTER_1),y
          tya
          clc
          adc #STONE_FRONT_DISTANCE
          tay
          cpy #39
          bcc -

          lda MOVE_STONE_POS_FRONT
          clc
          adc #2

-
          cmp #STONE_FRONT_DISTANCE
          bcc +
          sec
          sbc #STONE_FRONT_DISTANCE
          jmp -

+
          sta MOVE_STONE_POS_FRONT
          ldy MOVE_STONE_POS_FRONT

-
          lda #148
          sta (ZEROPAGE_POINTER_1),y
          lda #9
          sta (ZEROPAGE_POINTER_2),y
          tya
          clc
          adc #STONE_FRONT_DISTANCE
          tay
          cpy #39
          bcc -

.NoStones

step86.zip