Bresenham's Line Algorithm

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(signedness fixes)
Line 1: Line 1:
Previous article deleted due to crappiness. Here's an improved C++ version (as in the previous article plot() draws a pixel at (x, y):
+
Here's a C++ version (as in the previous article plot() draws a "dot" at (x, y):
  
#ifndef ABS
 
#  define ABS(x) ((x)>0?(x):-(x))
 
#endif
 
 
 
  ////////////////////////////////////////////////////////////////////////////////
 
  ////////////////////////////////////////////////////////////////////////////////
 
  void Bresenham(unsigned x1,
 
  void Bresenham(unsigned x1,
Line 11: Line 7:
 
     unsigned y2)
 
     unsigned y2)
 
  {
 
  {
     unsigned delta_x = ABS(x2 - x1) << 1;
+
     unsigned delta_x = (x2 > x1?x2 - x1:x1 - x2) << 1;
     unsigned delta_y = ABS(y2 - y1) << 1;
+
     unsigned delta_y = (y2 > y1?y2 - y1:y1 - y2) << 1;
 
   
 
   
 
     // if x1 == x2 or y1 == y2, then it does not matter what we set here
 
     // if x1 == x2 or y1 == y2, then it does not matter what we set here

Revision as of 02:21, 24 March 2007

Here's a C++ version (as in the previous article plot() draws a "dot" at (x, y):

////////////////////////////////////////////////////////////////////////////////
void Bresenham(unsigned x1,
    unsigned y1,
    unsigned x2,
    unsigned y2)
{
    unsigned delta_x = (x2 > x1?x2 - x1:x1 - x2) << 1;
    unsigned delta_y = (y2 > y1?y2 - y1:y1 - y2) << 1;

    // if x1 == x2 or y1 == y2, then it does not matter what we set here
    char ix = x2 > x1?1:-1;
    char iy = y2 > y1?1:-1;

    plot(x1, y1);

    if (delta_x >= delta_y)
    {
        // error may go below zero
        int error = delta_y - (delta_x >> 1);

        while (x1 != x2)
        {
            if (error >= 0)
            {
                if (error || (ix > 0))
                {
                    y1 += iy;
                    error -= delta_x;
                }
                // else do nothing
            }
            // else do nothing

            x1 += ix;
            error += delta_y;

            plot(x1, y1);
        }
    }
    else
    {
        // error may go below zero
        int error = delta_x - (delta_y >> 1);

        while (y1 != y2)
        {
            if (error >= 0)
            {
                if (error || (iy > 0))
                {
                    x1 += ix;
                    error -= delta_y;
                }
                // else do nothing
            }
            // else do nothing

            y1 += iy;
            error += delta_x;

            plot(x1, y1);
        }
    }
}
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