' D/BASIC port of the official GX physics/gravity.bas sample.
'
' Original sample and assets copyright (c) 2021 boxgaming, MIT licensed.
' This port keeps the official sample's controls, player, reusable bullets,
' gravity, platforms, and collision rules. Its original PNG sprites and GXM
' map ship in gx-gravity-assets; this alpha live path expresses that material
' with current GFX primitives until named resources join the browser provider.
IMPORT gx

CONST PLAYER = 0
CONST PLATFORM_ONE = 1
CONST PLATFORM_TWO = 2
CONST FLOOR_ENTITY = 3
CONST BULLET_FIRST = 4
CONST BULLET_COUNT = 10
CONST RIGHT = 2
CONST LEFT = 1
CONST SKY = 8456
CONST GROUND = 10697
CONST GROUND_EDGE = 21162
CONST PLAYER_RED = -1835
CONST PLAYER_WHITE = -1
CONST COIN_GOLD = -1120

DIM SHARED Scene(0 TO 7) AS INTEGER
DIM SHARED Entities(0 TO 139) AS INTEGER
DIM SHARED Camera(0 TO 1) AS INTEGER
DIM SHARED BulletAlive(0 TO 9) AS INTEGER
DIM SHARED BulletNext AS INTEGER
DIM SHARED Direction AS INTEGER
DIM SHARED AnimationTick AS INTEGER
DIM SHARED Paused AS INTEGER

DECLARE SUB EntitySetPosition(Slot AS INTEGER, X AS INTEGER, Y AS INTEGER)
DECLARE SUB EntitySetVelocity(Slot AS INTEGER, VX AS INTEGER, VY AS INTEGER)
DECLARE SUB StepPlayer()
DECLARE SUB StepBullets()
DECLARE SUB Shoot()
DECLARE SUB DrawMap()
DECLARE SUB DrawEntity(Slot AS INTEGER, Color AS INTEGER)
DECLARE SUB DrawPlayer()
DECLARE SUB DrawBullets()

WINDOW SUB OPEN()
  CALL GXSceneOpen(Scene(), 320, 192)
  CALL GXEntitySpawn(Entities(), PLAYER, 20, 0, 16, 20, 1)
  CALL GXEntitySpawn(Entities(), PLATFORM_ONE, 40, 140, 100, 20, 2)
  CALL GXEntitySpawn(Entities(), PLATFORM_TWO, 200, 80, 100, 20, 2)
  CALL GXEntitySpawn(Entities(), FLOOR_ENTITY, 0, 184, 320, 8, 2)
  Direction = RIGHT
  BulletNext = 0
  AnimationTick = 0
  Paused = 0
  SERVICE SET_TITLE("GX Gravity - official sample")
END SUB

WINDOW SUB DRAW()
  IF Paused = 0 THEN
    CALL GXSceneAdvance(Scene())
    CALL StepPlayer()
    CALL StepBullets()
    AnimationTick = AnimationTick + 1
    IF AnimationTick > 30000 THEN AnimationTick = 0
  END IF

  INTENT GFX.BEGIN_FRAME()
  INTENT GFX.FILL_RECT(0, 0, 320, 192, SKY)
  CALL DrawMap()
  CALL DrawEntity(PLATFORM_ONE, GROUND)
  CALL DrawEntity(PLATFORM_TWO, GROUND)
  CALL DrawEntity(FLOOR_ENTITY, GROUND)
  CALL DrawPlayer()
  CALL DrawBullets()
  INTENT GFX.DRAW_TEXT(8, 7, "A/D move   K jump   J fire   P pause", 2, PLAYER_WHITE, SKY)
  IF Paused <> 0 THEN
    INTENT GFX.FILL_RECT(112, 80, 96, 28, 0)
    INTENT GFX.DRAW_TEXT(129, 86, "PAUSED", 3, PLAYER_WHITE, 0)
  END IF
  INTENT GFX.PRESENT()
  SERVICE INVALIDATE()
END SUB

WINDOW SUB CLOSE()
END SUB

ON KEY SUB (K AS INTEGER)
  DIM EntityAt AS INTEGER
  EntityAt = GXEntityBase(Entities(), PLAYER)
  IF K = 65 OR K = 97 THEN
    Entities(EntityAt + GX_ENTITY_VX_AT) = -3
    Direction = LEFT
  END IF
  IF K = 68 OR K = 100 THEN
    Entities(EntityAt + GX_ENTITY_VX_AT) = 3
    Direction = RIGHT
  END IF
  IF K = 75 OR K = 107 THEN
    IF Entities(EntityAt + GX_ENTITY_VY_AT) = 0 THEN Entities(EntityAt + GX_ENTITY_VY_AT) = -9
  END IF
  IF K = 74 OR K = 106 THEN CALL Shoot()
  IF K = 80 OR K = 112 THEN Paused = NOT Paused
END SUB

SUB EntitySetPosition(Slot AS INTEGER, X AS INTEGER, Y AS INTEGER)
  DIM EntityAt AS INTEGER
  EntityAt = GXEntityBase(Entities(), Slot)
  Entities(EntityAt + GX_ENTITY_X_AT) = X
  Entities(EntityAt + GX_ENTITY_Y_AT) = Y
END SUB

SUB EntitySetVelocity(Slot AS INTEGER, VX AS INTEGER, VY AS INTEGER)
  DIM EntityAt AS INTEGER
  EntityAt = GXEntityBase(Entities(), Slot)
  Entities(EntityAt + GX_ENTITY_VX_AT) = VX
  Entities(EntityAt + GX_ENTITY_VY_AT) = VY
END SUB

SUB StepPlayer()
  DIM EntityAt AS INTEGER
  DIM Platform AS INTEGER
  DIM PlatformBase AS INTEGER
  DIM PreviousY AS INTEGER
  EntityAt = GXEntityBase(Entities(), PLAYER)
  PreviousY = Entities(EntityAt + GX_ENTITY_Y_AT)
  IF Entities(EntityAt + GX_ENTITY_VY_AT) < 8 THEN Entities(EntityAt + GX_ENTITY_VY_AT) = Entities(EntityAt + GX_ENTITY_VY_AT) + 1
  CALL GXEntityStep(Entities(), PLAYER)

  IF Entities(EntityAt + GX_ENTITY_X_AT) < 0 THEN Entities(EntityAt + GX_ENTITY_X_AT) = 0
  IF Entities(EntityAt + GX_ENTITY_X_AT) > 304 THEN Entities(EntityAt + GX_ENTITY_X_AT) = 304

  IF Entities(EntityAt + GX_ENTITY_VY_AT) >= 0 THEN
    FOR Platform = PLATFORM_ONE TO FLOOR_ENTITY
      PlatformBase = GXEntityBase(Entities(), Platform)
      IF PreviousY + 20 <= Entities(PlatformBase + GX_ENTITY_Y_AT) + 2 THEN
        IF GXEntitiesOverlap(Entities(), PLAYER, Platform) <> 0 THEN
          Entities(EntityAt + GX_ENTITY_Y_AT) = Entities(PlatformBase + GX_ENTITY_Y_AT) - 20
          Entities(EntityAt + GX_ENTITY_VY_AT) = 0
        END IF
      END IF
    NEXT Platform
  END IF

  IF Entities(EntityAt + GX_ENTITY_Y_AT) > 192 THEN
    CALL EntitySetPosition(PLAYER, 20, 0)
    CALL EntitySetVelocity(PLAYER, 0, 0)
  END IF

  IF Entities(EntityAt + GX_ENTITY_VX_AT) > 0 THEN Entities(EntityAt + GX_ENTITY_VX_AT) = Entities(EntityAt + GX_ENTITY_VX_AT) - 1
  IF Entities(EntityAt + GX_ENTITY_VX_AT) < 0 THEN Entities(EntityAt + GX_ENTITY_VX_AT) = Entities(EntityAt + GX_ENTITY_VX_AT) + 1
END SUB

SUB StepBullets()
  DIM I AS INTEGER
  DIM Slot AS INTEGER
  DIM EntityAt AS INTEGER
  DIM Platform AS INTEGER
  IF BULLET_COUNT <= 0 THEN EXIT SUB
  FOR I = 0 TO BULLET_COUNT - 1
    IF BulletAlive(I) <> 0 THEN
      Slot = BULLET_FIRST + I
      EntityAt = GXEntityBase(Entities(), Slot)
      IF Entities(EntityAt + GX_ENTITY_VY_AT) < 8 THEN Entities(EntityAt + GX_ENTITY_VY_AT) = Entities(EntityAt + GX_ENTITY_VY_AT) + 1
      CALL GXEntityStep(Entities(), Slot)
      FOR Platform = PLATFORM_ONE TO FLOOR_ENTITY
        IF GXEntitiesOverlap(Entities(), Slot, Platform) <> 0 THEN BulletAlive(I) = 0
      NEXT Platform
      IF Entities(EntityAt + GX_ENTITY_X_AT) < -16 OR Entities(EntityAt + GX_ENTITY_X_AT) > 320 THEN BulletAlive(I) = 0
      IF Entities(EntityAt + GX_ENTITY_Y_AT) > 192 THEN BulletAlive(I) = 0
    END IF
  NEXT I
END SUB

SUB Shoot()
  DIM Slot AS INTEGER
  DIM EntityAt AS INTEGER
  DIM PlayerBase AS INTEGER
  Slot = BULLET_FIRST + BulletNext
  IF Entities(GXEntityBase(Entities(), Slot) + GX_ENTITY_ALIVE_AT) = 0 THEN
    CALL GXEntitySpawn(Entities(), Slot, 0, 0, 10, 10, 3)
  END IF
  EntityAt = GXEntityBase(Entities(), Slot)
  PlayerBase = GXEntityBase(Entities(), PLAYER)
  IF Direction = RIGHT THEN
    Entities(EntityAt + GX_ENTITY_X_AT) = Entities(PlayerBase + GX_ENTITY_X_AT) + 12
    Entities(EntityAt + GX_ENTITY_VX_AT) = 6
  ELSE
    Entities(EntityAt + GX_ENTITY_X_AT) = Entities(PlayerBase + GX_ENTITY_X_AT) - 6
    Entities(EntityAt + GX_ENTITY_VX_AT) = -6
  END IF
  Entities(EntityAt + GX_ENTITY_Y_AT) = Entities(PlayerBase + GX_ENTITY_Y_AT) + 6
  Entities(EntityAt + GX_ENTITY_VY_AT) = -3
  BulletAlive(BulletNext) = -1
  BulletNext = BulletNext + 1
  IF BulletNext >= BULLET_COUNT THEN BulletNext = 0
END SUB

SUB DrawMap()
  DIM Y AS INTEGER
  INTENT GFX.FILL_RECT(0, 64, 48, 128, GROUND_EDGE)
  INTENT GFX.FILL_RECT(16, 80, 32, 112, GROUND)
  INTENT GFX.FILL_RECT(272, 128, 48, 64, GROUND_EDGE)
  INTENT GFX.FILL_RECT(208, 160, 64, 32, GROUND_EDGE)
  FOR Y = 64 TO 176 STEP 16
    INTENT GFX.FILL_RECT(0, Y, 2, 14, PLAYER_WHITE)
  NEXT Y
END SUB

SUB DrawEntity(Slot AS INTEGER, Color AS INTEGER)
  DIM EntityAt AS INTEGER
  EntityAt = GXEntityBase(Entities(), Slot)
  INTENT GFX.FILL_RECT(Entities(EntityAt + GX_ENTITY_X_AT), Entities(EntityAt + GX_ENTITY_Y_AT), Entities(EntityAt + GX_ENTITY_WIDTH_AT), Entities(EntityAt + GX_ENTITY_HEIGHT_AT), Color)
  INTENT GFX.FILL_RECT(Entities(EntityAt + GX_ENTITY_X_AT), Entities(EntityAt + GX_ENTITY_Y_AT), Entities(EntityAt + GX_ENTITY_WIDTH_AT), 2, GROUND_EDGE)
END SUB

SUB DrawPlayer()
  DIM EntityAt AS INTEGER
  DIM X AS INTEGER
  DIM Y AS INTEGER
  DIM StepFrame AS INTEGER
  EntityAt = GXEntityBase(Entities(), PLAYER)
  X = Entities(EntityAt + GX_ENTITY_X_AT)
  Y = Entities(EntityAt + GX_ENTITY_Y_AT)
  StepFrame = GXAnimationFrame(0, 2, AnimationTick, 6)
  INTENT GFX.FILL_RECT(X + 4, Y, 8, 5, PLAYER_WHITE)
  INTENT GFX.FILL_RECT(X + 3, Y + 5, 10, 6, PLAYER_RED)
  INTENT GFX.FILL_RECT(X + 2, Y + 11, 12, 7, PLAYER_RED)
  IF StepFrame = 0 THEN
    INTENT GFX.FILL_RECT(X + 3, Y + 18, 4, 2, 0)
    INTENT GFX.FILL_RECT(X + 10, Y + 18, 4, 2, 0)
  ELSE
    INTENT GFX.FILL_RECT(X + 5, Y + 18, 4, 2, 0)
    INTENT GFX.FILL_RECT(X + 8, Y + 18, 4, 2, 0)
  END IF
  IF Direction = RIGHT THEN
    INTENT GFX.FILL_RECT(X + 10, Y + 3, 2, 2, 0)
  ELSE
    INTENT GFX.FILL_RECT(X + 4, Y + 3, 2, 2, 0)
  END IF
END SUB

SUB DrawBullets()
  DIM I AS INTEGER
  DIM Slot AS INTEGER
  DIM EntityAt AS INTEGER
  DIM X AS INTEGER
  DIM Y AS INTEGER
  FOR I = 0 TO BULLET_COUNT - 1
    IF BulletAlive(I) <> 0 THEN
      Slot = BULLET_FIRST + I
      EntityAt = GXEntityBase(Entities(), Slot)
      X = Entities(EntityAt + GX_ENTITY_X_AT)
      Y = Entities(EntityAt + GX_ENTITY_Y_AT)
      INTENT GFX.FILL_RECT(X + 2, Y, 6, 10, COIN_GOLD)
      INTENT GFX.FILL_RECT(X, Y + 2, 10, 6, COIN_GOLD)
      INTENT GFX.FILL_RECT(X + 4, Y + 2, 2, 6, PLAYER_WHITE)
    END IF
  NEXT I
END SUB