8bitworkshop/presets/vcs/ecs/velocity.ecs

//#resource "vcs-ca65.h"

import "vcslib.ecs"
import "sprites.ecs"

component TinyVelX
// TODO: -8..7? packed?
  xvel: 0..15 default 8
end
component TinyVelY
// TODO: -8..7? packed?
  yvel: 0..15 default 8
end

system TinyMover
  locals 1
  on postframe do foreach [HasXpos,TinyVelX]
---
  lda {{<FrameCount:frame}}
  and #7		; reduce frame # to 0..7
  tay
  lda {{^VMaskTable}},y	; lookup frame bit mask
  ldy {{<xvel}}		; xvel from 0..15
  and {{^VAndTable}},y	; mask with velocity table
  jeq @nomove		; no bits set? no move
  lda {{^DeltaVTable}},y	; lookup position delta
  clc
  adc {{<xpos}}		; add to coordinate
  sta {{<xpos}}		; store to coordinate
  {{!xmoved}}		; maybe modify it?
@nomove:
---
  on postframe do foreach [HasXpos,TinyVelY]
---
  lda {{<FrameCount:frame}}
  and #7		; reduce frame # to 0..7
  tay
  lda {{^VMaskTable}},y	; lookup frame bit mask
  ldy {{<yvel}}		; xvel from 0..15
  and {{^VAndTable}},y	; mask with velocity table
  jeq @nomove		; no bits set? no move
  lda {{^DeltaVTable}},y	; lookup position delta
  clc
  adc {{<ypos}}		; add to coordinate
  sta {{<ypos}}		; store to coordinate
  {{!ymoved}}		; maybe modify it?
@nomove:
---// set player reflection bit
   on xmoved do with [Sprite]
   ---
   pha
   lda {{<plyrflags}}
   and #255-8
   ora {{^VReflectTab}},y
   sta {{<plyrflags}}
   and #7
   tay
   lda {{^VXLimitTab}},y
   sta {{$0}}
   pla
   ---
// TODO: x/y limits should be properties
   on xmoved do with [HasXpos]
   ---
   cmp #2
   jcc @left
   cmp {{$0}}
   jcc @skip
@right:
   {{!xlimit_right}}
   jne @skip
@left:
   {{!xlimit_left}}
@skip:
   ---
   on xlimit_right do with [HasXpos]
   ---
   lda {{$0}}
   sta {{<xpos}}
   ---
   on xlimit_left do with [HasXpos]
   ---
   lda #2
   sta {{<xpos}}
   ---

end

resource DeltaVTable ---
; this table tells us which direction to move
; for each of the 16 velocity values (-1, 0 or +1)
	.byte $fe,$fe,$ff,$ff,$ff,$ff,$ff,$00
        .byte $00,$01,$01,$01,$01,$01,$02,$02
---

resource VAndTable ---
; this table contains a bitmask for each of the 16
; velocity values -- it's ANDed with a global shift
; register that tells us which frames to update position

	.byte %11111111 ;16/8
        .byte %01110111 ;12/8
	.byte %11111111 ;8/8
        .byte %01110111 ;6/8
        .byte %10101010 ;4/8
        .byte %01010010 ;3/8
        .byte %10001000 ;2/8
        .byte %00000000 ;0
        .byte %00000000 ;0
        .byte %10001000 ;2/8
        .byte %01010010 ;3/8
        .byte %10101010 ;4/8
        .byte %01110111 ;6/8
	.byte %11111111 ;8/8
        .byte %01110111 ;12/8
	.byte %11111111 ;16/8
---

resource VMaskTable ---
	.byte %00000001
	.byte %00000010
	.byte %00000100
	.byte %00001000
	.byte %00010000
	.byte %00100000
	.byte %01000000
	.byte %10000000
---

resource VReflectTab ---
	.byte 8,8,8,8,8,8,8,8
        .byte 0,0,0,0,0,0,0,0
---

/*
if 000,         X               one copy
if 001,         X X             two copies, close
if 010,         X   X           two copies, medium
if 011,         X X X           three copies, close
if 100,         X       X       Two copies, far
if 101,         XX              one copy, double width
if 110,         X   X   X       3 copies, medium
if 111,         XXXX            one copy, quad width
*/
resource VXLimitTab ---
	.byte 152-8*1
        .byte 152-8*3
        .byte 152-8*5
        .byte 152-8*5
        .byte 152-8*9
        .byte 152-8*2
        .byte 152-8*9
        .byte 152-8*4
---