# Bresenham's Line Algorithm

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);
}
}
}
```

And here 's a Ruby version, it returns an array of points, each being an hash with 2 elements (x and y)

```  def get_line(x0,x1,y0,y1)
points = []
steep = ((y1-y0).abs) > ((x1-x0).abs)
if steep
x0,y0 = y0,x0
x1,y1 = y1,x1
end
if x0 > x1
x0,x1 = x1,x0
y0,y1 = y1,y0
end
deltax = x1-x0
deltay = (y1-y0).abs
error = (deltax / 2).to_i
y = y0
ystep = nil
if y0 < y1
ystep = 1
else
ystep = -1
end
for x in x0..x1
if steep
points << {:x => y, :y => x}
else
points << {:x => x, :y => y}
end
error -= deltay
if error < 0
y += ystep
error += deltax
end
end
return points
end
```