# Bresenham's Line Algorithm

(Difference between revisions)

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);
}
}
}