PB Parallax Starfield

; ------------------------------------------------------------
;
;   Parallax Starfield (4 layers)
;
;   Code by aNdy/AL/Cosine in 2018
;
;   https://andyvaisey.blogspot.com/p/code.html
;
; ------------------------------------------------------------

;- INITIALISE ENVIRONMENT ------------------------------------

InitKeyboard()
InitSprite()

;- CREATE VARIABLES ------------------------------------------

#XRES = 800
#YRES = 600
#LAYER1SPEED = 1
#LAYER2SPEED = 3
#LAYER3SPEED = 5
#LAYER4SPEED = 10

;- PROCEDURES ------------------------------------------------

Procedure OpenMainWindow()

  OpenWindow(0,0,0,#XRES,#YRES,"Parallax Stars!",#PB_Window_ScreenCentered)
  OpenWindowedScreen(WindowID(0),0,0,#XRES,#YRES)

EndProcedure

Procedure CreateStarfields()

  Global sp_BKGRDSTAR = CreateSprite(#PB_Any,#XRES,#YRES)
  StartDrawing(SpriteOutput(sp_BKGRDSTAR))
  For n=0 To 999
    Plot(Random(#XRES-1),Random(#YRES-1),RGB(100,100,100))
  Next
  StopDrawing()

  Global sp_MDGRDSTAR = CreateSprite(#PB_Any,#XRES,#YRES)
  StartDrawing(SpriteOutput(sp_MDGRDSTAR))
  For n=0 To 299
    Plot(Random(#XRES-1),Random(#YRES-1),RGB(150,150,150))
  Next
  StopDrawing()

  Global sp_FTGRDSTAR = CreateSprite(#PB_Any,#XRES,#YRES)
  StartDrawing(SpriteOutput(sp_FTGRDSTAR))
  For n=0 To 199
    Plot(Random(#XRES-1),Random(#YRES-1),RGB(200,200,200))
  Next
  StopDrawing()

  Global sp_CLGRDSTAR = CreateSprite(#PB_Any,#XRES,#YRES)
  StartDrawing(SpriteOutput(sp_CLGRDSTAR))
  For n=0 To 19
    Plot(Random(#XRES-1),Random(#YRES-1),RGB(255,255,255))
  Next
  StopDrawing()

EndProcedure

Procedure DrawStarfields()

  Shared bgx1, bgx2, bgx3, bgx4

  For s1 = 0 To 1
    For s2 = 0 To 1
      DisplayTransparentSprite(sp_BKGRDSTAR,#XRES*s1-bgx1,#YRES*s2)
      DisplayTransparentSprite(sp_MDGRDSTAR,#XRES*s1-bgx2,#YRES*s2)
      DisplayTransparentSprite(sp_FTGRDSTAR,#XRES*s1-bgx3,#YRES*s2)
      DisplayTransparentSprite(sp_CLGRDSTAR,#XRES*s1-bgx4,#YRES*s2)
    Next
  Next

  bgx1+#LAYER1SPEED : If bgx1 > #XRES-1 : bgx1=0 : EndIf
  bgx2+#LAYER2SPEED : If bgx2 > #XRES-1 : bgx2=0 : EndIf
  bgx3+#LAYER3SPEED : If bgx3 > #XRES-1 : bgx3=0 : EndIf
  bgx4+#LAYER4SPEED : If bgx4 > #XRES-1 : bgx4=0 : EndIf

EndProcedure

;- BEGIN PROGRAM ----------------------------------------------------

OpenMainWindow()
CreateStarfields()
HideWindow(0,#False)

;- MAIN PROGRAM LOOP ------------------------------------------------

Repeat

  WaitWindowEvent(1)
  ClearScreen(0)
  DrawStarfields()
  FlipBuffers()
  ExamineKeyboard()

Until KeyboardPushed(#PB_Key_Escape)

;- EXIT PROGRAM ----------------------------------------------------

FreeSprite(#PB_All)
CloseWindow(#PB_All)

End