Bresenham's Line Algorithm

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m (Breshenham's Line Algorithm moved to Bresenham's Line Algorithm: fix spelling of Bresenham)
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[[Category:Algorithms]]
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[[Category:Articles]]

Revision as of 17:55, 22 March 2009

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

#include <cmath>

////////////////////////////////////////////////////////////////////////////////
void Bresenham(int x1,
    int y1,
    int x2,
    int y2)
{
    int delta_x = std::abs(x2 - x1) << 1;
    int delta_y = std::abs(y2 - y1) << 1;

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