Displaying Graphics a line by line Preview

[kevin]

  Displaying Graphics a line by line Preview


    While checking out Steve's latest ray tracer,  I started thinking about the preview mode.  Which display the ray traced image scan line by scan line.  In the ray tracer this drawn to an off screen FX image, which is then drawn to the display at the end of each scanline.   Which involves drawing the FX image to the screen and syncing the display. .  But if we draw the fx image we're actually copying all the pixel data to the output every scanline.   This impacts the rendering performance;  what we could do is just draw the line from the image to the screen.    We're still syncing but we're not copying the data every row.

PlayBASIC Code: [Select]

   width=1400
   height=700

   openscreen width,height,32,1


   screen = newfximage(Width,height)

   global Colour

   TestCount=3

   t=timer()
   For lp=1 to TestCount
      Preview1(Screen,Width,height)
   next
   t1=timer()-t

   t=timer()
   For lp=1 to TestCount
      Preview2(Screen,Width,height)
   next
   t2=timer()-t


   cls 
   print t1
   print t2
   sync
   waitkey
      


Function Preview1(Screen,Width,height)
   
         
         For ylp=0 to height-1
            
            rendertoimage Screen   
               lockbuffer
               ThisRGB=Point(0,0)
                  for xlp=0 to width-1
                              
                     fastdot xlp,ylp,colour               
                     colour+=Xlp
                  next
               unlockbuffer

            rendertoscreen
            drawimage Screen,0,0,false
            sync
         next
   
EndFunction


Function Preview2(Screen,Width,height)
   
         
         For ylp=0 to height-1
            
            rendertoimage Screen   
               lockbuffer
               ThisRGB=Point(0,0)
                  for xlp=0 to width-1
                              
                     fastdot xlp,ylp,colour               
                     colour+=Xlp
                  next
               unlockbuffer

            rendertoscreen
            
            ScreenViewport 0,ylp,Width,ylp+1
            drawimage Screen,0,0,false
            
            sync
         next
            ScreenViewport 0,0,Width,height
            
EndFunction
   

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