From Poke to Pointers (screen fill examples)

[kevin]

   From Poke to Pointers (screen fill examples)  (2018-12-11)



   Example #1 - Fill Screen using PokeInt

PlayBASIC Code: [Select]

      Do

         frames++
         ThisColour+=$10203
         
         t=timer()
            FillScreen1(ThisColour)
         tt#+=Timer()-t
                  
         
         text 0,0,"Average Fill Time:"+str$(tt#/frames)
         
         Sync
                  
         
   loop spacekey()
   end   





Function FillScreen1(ThisColour)
   RendertoScreen
   lockbuffer
      Width   =GetSurfaceWidth()
      Height=GetSurfaceHeight()
   
      Ptr   =   GetImagePtr(0)
      Pitch = GetImagePitch(0)
   
       ThisRGB=point(0,0)
   
      for Ylp=0 to Height-1
         
         RowAddress = Ptr + (Ylp * Pitch)      
         for Xlp=0 to Width-1
               PokeInt RowAddress+(Xlp*4), ThisColour 
         next   
      next
   
   unlockbuffer
   
EndFunction



 

   Example #2 - Fill Screen using pointer

PlayBASIC Code: [Select]

      Do

         frames++
         ThisColour+=$10203
         
         t=timer()
            FillScreen2(ThisColour)
         tt#+=Timer()-t
                  
         
         text 0,0,"Average Fill Time:"+str$(tt#/frames)
         
         Sync
                  
         
   loop spacekey()
   end   




Function FillScreen2(ThisColour)
   RendertoScreen
   lockbuffer
      Width   =GetSurfaceWidth()
      Height=GetSurfaceHeight()
   
      Ptr   =   GetImagePtr(0)
      Pitch = GetImagePitch(0)
   
       ThisRGB=point(0,0)
   
      for Ylp=0 to Height-1
         
         ; define pointer that read/writes Integers 
         Dim RowPtr as Integer Pointer
         ; Comute the first pixel on this row 
         RowPtr = Ptr + (Ylp * Pitch)      

         for Xlp=0 to Width-1
               ; de reference (WRITE TO) this pointer, same as POKEINT
               *RowPtr=ThisColour
               
               ; add 1 to this pointer.  Since the pointer is an integer
               ; adding 1 is actually moving 4 bytes ahead to the next pixel
               RowPtr++ 
         next   
      next
   
   unlockbuffer
   
EndFunction

 

   Example #3 - Fill Screen using typed pointer, with a static array field

PlayBASIC Code: [Select]

      Do

         frames++
         ThisColour+=$10203
         
         t=timer()
            FillScreen3(ThisColour)
         tt#+=Timer()-t
                  
         
         text 0,0,"Average Fill Time:"+str$(tt#/frames)
         
         Sync
                  
         
   loop spacekey()
   end   




      Type tPixelRow
               Pixels(10000)
      EndType



Function FillScreen3(ThisColour)
   RendertoScreen
   lockbuffer
      Width   =GetSurfaceWidth()
      Height=GetSurfaceHeight()
   
      Ptr   =   GetImagePtr(0)
      Pitch = GetImagePitch(0)
   
       ThisRGB=point(0,0)
   
      for Ylp=0 to Height-1
         
         ; define typed pointer.  Writing to it is just like
         ; Peek / poke at this location with and offset 
         Dim Row as tPixelRow Pointer
         ; Comute the first pixel on this row 
         Row = Ptr + (Ylp * Pitch)      

         for Xlp=0 to Width-1
               ; Write to the address of this pointer with offset of the array
               ; index.   Since the Pixels array is the first field in the type
               ; it'll have an offset of zero from where ever the pointer is
               ; pointing
               
               ; now since the array is 32bit, it's the same as going
               ; pokeint RowAddress+(Xlp*4), ThisColour
               Row.Pixels(xlp)=ThisColour
         next   
      next
   
   unlockbuffer
   
EndFunction

   Example #4 - Fill Screen using typed pointer, with a static array field (UNROLLED)

PlayBASIC Code: [Select]

      Do

         frames++
         ThisColour+=$10203
         
         t=timer()
            FillScreen3_UNROLLED(ThisColour)
         tt#+=Timer()-t
                  
         
         text 0,0,"Average Fill Time:"+str$(tt#/frames)
         
         Sync
                  
         
   loop spacekey()
   end   




      Type tPixelRow
               Pixels(7)
      EndType







Function FillScreen3_UNROLLED(ThisColour)
   RendertoScreen
   lockbuffer
      Width   =GetSurfaceWidth()
      Height=GetSurfaceHeight()
   
      Ptr   =   GetImagePtr(0)
      Pitch = GetImagePitch(0)
   
       ThisRGB=point(0,0)
   
   
      ; The Number of 8 pixel chunks in this width
      Chunks = Width / 8
      
      ; the left over pixels on this row
      LeftOverPixels = Width-( Chunks * 8 )
   
      for Ylp=0 to Height-1
         
         ; define typed pointer.  Writing to it is just like
         ; Peek / poke at this location with and offset 
         Dim Row as tPixelRow Pointer
         ; Comute the first pixel on this row 
         Row = Ptr + (Ylp * Pitch)      


   
         for Xlp=0 to Width-1 step 8
            
            
               ; write to this address - Add the offset of Pixels array
               ;                         and compute the 0 pixel 
               Row.Pixels(0)=ThisColour

               ; write to this address - Add the offset of Pixels array
               ;                         and compute the 1 pixel 

               Row.Pixels(1)=ThisColour
               Row.Pixels(2)=ThisColour
               Row.Pixels(3)=ThisColour
               Row.Pixels(4)=ThisColour
               Row.Pixels(5)=ThisColour
               Row.Pixels(6)=ThisColour
               Row.Pixels(7)=ThisColour
               
               Row= Row + Sizeof(tPixelRow)
         next   
      
      
         for Xlp=0 to leftOvers-1
               Row.Pixels(xlp)= ThisColour
         next      
         
      next
   
   unlockbuffer
   
EndFunction

[stevmjon]

comparing these examples makes pointers clearer to understand.

example #4 :
LeftOverPixels = Width - (Chunks*8)

* the multiply by 8 is being replaced with a smiley face

[kevin]

 
   ahh..  yeah,  i've corrected the code above.  It occurs because the custom tags are post processed as part of the broads theme, some any sequence of characters that just happens to be smiley can leak through into code blocks.