C64 Styled Sprite Rendering Example

[kevin]

 C64 Styled Sprite Rendering Example

   This snippet of code is recreating how C64 sprites are set out in memory.   C64 Sprites have two basic modes,  High resolution and MultiColour resolution.

    High Resolution sprites are only one 1 colour.   So each bit in the sprite represents a pixel on screen.  The pixels are coloured either as the background colour (0 = transparent/ mask colour for us),  or 1 for the Sprites unique colour.     So a bit pattern of %0011  draws a pair of transparent pixels followed by a pair of 'sprite colour' pixels.


   Multi colour sprites are 4 colour and half the horizontal resolution of high resolution sprites.  They're the same on screen width (24 pixels), but in order to index the 4 possible colours, each pixel is made up from a pair of bits.    Since it's using two bits per pixel,  our numeric range increases from 2 possible states to 4 possible states

   ie.

     %00  = palette(0)
     %01  = palette(1)
     %10  = palette(2)
     %11  = palette(3)

    In this demo palette(0) is output images transparent colour, which will be black by default.     Anyway the following bit pattern of %0011  draws two pixels (each is two pixels wide).    The first pixel is %00 is palette(0) and thus the transparent colour and should be ignored, the second is %11 (Palette(3), which will be whatever colour passed to the function.  

PlayBASIC Code: [Select]

; PROJECT : C64-Sprite-Render
; AUTHOR  : Kevin Picone
; CREATED : 3/26/2013
; EDITED  : 3/26/2013
; ---------------------------------------------------------------------


; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
; --[ C64 Styled Sprite Render (to IMage) ]-------------------------------------
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------



      Cls 255

      ; render to set of data out as an image      
      TestIMage =C64_Styled_Sprite_Render("TestSprite",$ffffff,$ff0000,$0000ff)

      ; draw the image 
      DrawImage TestImage,100,100,0



      ; render to set of data out as an image      
      RectIMage =C64_Styled_Sprite_Render("RectSprite",$ffffff,$ff0000,$0000ff)

      ; draw the image 
      DrawImage RectImage,200,100,0

      
      sync
      waitkey
      
      
      
      
      
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
; --[ C64 Styled Sprite Render (to IMage) ]-------------------------------------
; ------------------------------------------------------------------------------
; ------------------------------------------------------------------------------
;
;  This Function draws a set of data statements that form an emulation of C64
; sprite memory is set out.  C64 Sprites are  24 pixels by 21 rows high.  Which
; isn't much to work with today given the resolution of the screens we use, but
; back then when lowres (320*200) was common, that resolution was reaonable.
;
; ------------------------------------------------------------------------------


      ; Since the c64 sprites are so small, this constant allows us to control
      ; the amount of linear scaling applied to the post processed image. 
      ; Setting to 2 for example, will double the size of each pixel.. 
      Constant C64_Sprite_Scalar      =2

      
      ; Sprites can either be Hires (1 colour) or Mulicolour (4 colour)
      ; Multicolour sprites use bit pairs to get the colour index, this halves
      ; the resolution on the horizontal resolution

      ; Multicolour bit pairs
      
      ;  %00 =  Palete(0)
      ;  %01 =  Palete(1)
      ;  %10 =  Palete(2)
      ;  %11 =  Palete(3)

      
      Constant HiRes_Sprite          =1
      Constant MultiColour_Sprite   =2
      


Function  C64_Styled_Sprite_Render(DataID$,Colour1,Colour2,COlour3)

      oldsurface=getsurface()
      oldpos=GetDataPOinter()
      Restore DATAID$
      
      SkipMe$=ReadData$()
      ColourFormat = ReadData()

      Thisimage=NewIMage(24,21,2)

      Dim Palette(3)
      Palette(0)=0
      Palette(1)=Colour1
      Palette(2)=Colour2
      Palette(3)=Colour3

      rendertoimage ThisImage
      Lockbuffer
      ThisRGB=POint(0,0)

      For ylp =0 to 20
         RowBits=ReadData()

         Xpos=23
         Select ColourFormat
               case HiRes_Sprite
                  for Xpos=23 to 0 step -1
                        FastDot Xpos,ylp,Palette(RowBits and 1)
                        RowBits/=2                        
                  next       

               case MultiColour_Sprite
                  for Xpos=22 to 0 step -2
                        ThisRgb=Palette(RowBits and 3)
                        FastDot Xpos,ylp,ThisRGB
                        FastDot Xpos+1,ylp,ThisRGB
                        RowBits/=4                        
                  next       
               
         endselect               
      
      next
      unLockbuffer



      rendertoimage oldsurface
      ScaleImage ThisImage,C64_Sprite_Scalar,C64_Sprite_Scalar,0

      restore OldPos

EndFunction ThisIMage


 ; ---------------------------------------
 ; Sprite are 24*21 pixels so 3 bytes wide and 21 rows high
 ; ---------------------------------------

 /*  
      Black Template sprite data

     Data "SPRITE_1"
     Data Colour format  (Hires =1 , Multicolour=2)
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000
     Data %000000000000000000000000

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