Alpha Channel

[kevin]

  The following  provides a pretty simple function that creates dulled edge around an images alpha channel.  Alpha Channel is support in 32bit mode.    To create an image with Alpha channel use the new PrepareAFXIMage command.   Then render to it as normally.


Use  ARGB(A,R,G,B) to build colours with alpha channel

RGBA() reads the A channel from a ARGB colour value

PlayBASIC Code: [Select]

 CreateImage 100,800,600
 rendertoimage 100
 shadebox 0,0,800,600,0,255,$80a0cc,$ff00ff
 
 
 Height=100
 Width=100

  Createimage 1,Width,Height
  Preparefximage 1
  FillIMage(1)


  Createimage 2,Width,Height
  PrepareAFXimage 2
  FillIMage(2)
      
      
   do
         drawimage 100,x,ypos,false         
         
         for xlp=50 to 700 step 200
            drawimage 1,xlp,100,true
            drawimage 2,xlp,200,true
         next   

   
      sync
   loop
   


Function FillIMage(ThisImage)
   rendertoimage ThisIMage
   w=GetIMageWidth(Thisimage)
   h=GetIMageheight(Thisimage)
   ellipse w/2,h/2,w/2,h/2,true
   CreateImageAlphaChannelFilter(ThisImage)
   rendertoscreen
endfunction


   ; This function dulls the pixels on the start/edn of each row of image

Function CreateImageAlphaChannelFilter(ThisImage)
   if GetImageStatus(thisImage)=true
      DestSurface=getsurface()   

      RgbMaskIMage ThisImage,$00ffffff


      TransparentColour=GetImageMaskColour(ThisIMage)   and $ffffff
      RenderToImage ThisImage
      Width=GetImageWidth(ThisImage)-1

      Dim Row(Width)
         
      For ylp=0 to getimageheight(ThisImage)-1
         firstsolid=false

         ; copy a row of pixels to this array
         For xlp=0 to width
            Row(xlp)=FastPoint(xlp,ylp)
         next

         ; scan row and set the first an last pixels
         ; of a row to 50% alpha..       
         For xlp=0 to Width
            c=Row(xlp)
            if C=TransparentColour

                  if xlp>0
                     oldc=Row(xlp-1)
                     if RgbA(OldC)=255   
                        Row(xlp-1)=(oldc and $ffffff) or $80000000
                     endif
                  endif
               
               AlphaLevel=$0000000
               FirstSolid=false

            else
               if   firstsolid=false
                  AlphaLevel=$80000000
               else
                  AlphaLevel=$ff000000
               endif
               firstsolid=true
            endif
            Row(xlp)=C or AlphaLevel
         next

         ; copy the row back to the image
         For xlp=0 to Width
            fastdot xlp,ylp,Row(xlp)
         next

      next

      rendertoimage DestSurface
   endif   

EndFunction

   Note: Today it's recommended users create AFX images in AFX format directly via CreateImage, rather than creating an image (Video/FX)  and then converting it to AFX)

[ale870]

Hi,

I have version 1.48 but I cannot find anywhere, in help file, info about rgba or ARGB.
More, I cannot find any info about Blitimage.

Can you give me more info about these functions? Do they work in my version (compiler: V1.48, IDE: V.1.1.5.b2)

Thank you!

[kevin]

 There in the latest beta V1.48C.  See announcement here (login required).


For BlitImage use search in forums.

[stef]

8 white filled circles (all the same) on a shaded ground. Where is the joke?

[kevin]

  That's about it, it's not meant to be pretty example, it's a functional example.   It demonstrates how that the transparency of each pixel can be individually controlled  the alpha channel, in AFX surfaces.  

PlayBASIC Code: [Select]

 CreateImage 100,800,600
 RenderToImage 100
 ShadeBox 0,0,800,600,0,255,$80a0cc,$ff00ff
 
 
 Height=100
 Width=100
   ink $808080

  Createimage 1,Width,Height,2
  FillIMage(1)

  Createimage 2,Width,Height,8
  FillIMage(2)
      
   do
   
         drawimage 100,x,ypos,false         
         for xlp=50 to 700 step 200
            drawimage 1,xlp,100,true
            drawimage 2,xlp,200,true
         next   
   
      sync
   loop
   


Function FillIMage(ThisImage)
   rendertoimage ThisIMage
      w=GetIMageWidth(Thisimage)
      h=GetIMageheight(Thisimage)
      ellipse w/2,h/2,w/2,h/2,true
      CreateImageAlphaChannelFilter(ThisImage)
   rendertoscreen
endfunction



   ; This function dulls the pixels on the start/edn of each row of image
Function CreateImageAlphaChannelFilter(ThisImage)
   if GetImageStatus(thisImage)=true
      DestSurface=getsurface()   

      rgbmaskImage ThisIMage,$00ffffff

      TransparentColour=GetImageMaskColour(ThisIMage)   and $ffffff
      Width=GetImageWidth(ThisImage)-1
         
      RenderToImage ThisImage
      lockbuffer
      NullPoint=Point(0,0)
      For ylp=0 to getimageheight(ThisImage)-1

         For xlp=0 to width
            c=Point(xlp,ylp) and $ffffff
            if c
               fastdot xlp,ylp,c or lsl32(xlp,24)
            endif
         next

      next
      unlockbuffer

      rendertoimage DestSurface
   endif   

EndFunction

  (Code Corrected (2012 - Oct -9th) Old versions of PB would draw AFX surfaces with  transparency always, now it's optional)