Bresenham ALGORITHM

mxg331 · 2009-05-22 21:01

I've built a memory·mapped VGA interface using the SX 48.· I've implemented many video functions such as Sprites, draw pixel, and draw box but the line has got me stumped. Does anyone know how to implement a line using the Bresenham ALGORITHM or otherwise?· Thanks!

Post Edited (mxg331) : 5/23/2009 12:28:41 AM GMT

Leon · 2009-05-22 22:13

Don't you mean the Bresenham algorithm?

Leon

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mxg331 · 2009-05-23 00:28

Yes, but any line algorithm will do.· I've already developed my own but it has many issues.

Bean · 2009-05-23 02:04

Here is one in SX/B

' Variables used by graphics subroutines 
cnt   VAR Byte 
cnt2  VAR Byte 
x1    VAR Byte 
x2    VAR Byte 
y1    VAR Byte 
y2    VAR Byte 
color VAR Byte 

Line SUB 4 

Line: ' (x1,y1,x2,y2) ; Set color before calling 
  x1 = __PARAM1 
  y1 = __PARAM2 
  x2 = __PARAM3 - x1 
  y2 = __PARAM4 - y1 
  IF x2 >= y2 THEN 
    cnt2 = x2 >> 1 
    FOR cnt = 0 TO x2 
      PutPixel x1, y1, color 
      INC x1 
      IF cnt2 >= y2 THEN 
        cnt2 = cnt2 - y2 
      ELSE 
        cnt2 = cnt2 - y2 
        cnt2 = cnt2 + x2 
        INC y1 
      ENDIF 
    NEXT 
  ELSE 
    cnt2 = y2 >> 1 
    FOR cnt = 0 TO y2 
      PutPixel x1, y1, color 
      INC y1 
      IF cnt2 >= x2 THEN 
        cnt2 = cnt2 - x2 
      ELSE 
        cnt2 = cnt2 - x2 
        cnt2 = cnt2 + y2 
        INC x1 
      ENDIF 
    NEXT 
  ENDIF 
  x2 = x1 
  y2 = y1 
RETURN

Bean

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mxg331 · 2009-05-23 22:25

Thank you for your response.· As I'm sure you can appreciate, the process I'm·implementing·is very time critical.· I would prefer (need) a line algorithm in SX assembly.· Thanks to all who are thinking about this!

JonnyMac · 2009-05-23 22:57

Remember, SX/B compiles to Assembly and you may find that Bean's code works as well as you need. If nothing else, run it through the compiler and then take the output and see if you can optimize it (I do this a lot as it helps me learn Assembly).

Bresenham ALGORITHM

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