Bresenham's Line Algorithm
From RogueBasin
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//////////////////////////////////////////////////////////////////////////////// | //////////////////////////////////////////////////////////////////////////////// | ||
void Bresenham(int x1, | void Bresenham(int x1, | ||
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int y2) | int y2) | ||
{ | { | ||
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// 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 | ||
signed char ix = x2 > x1?1:-1; | signed char ix = x2 > x1?1:-1; | ||
signed char iy = y2 > y1?1:-1; | signed char iy = y2 > y1?1:-1; | ||
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| + | int delta_x = ix > 0?x2 - x1:x1 - x2; | ||
| + | int delta_y = iy > 0?y2 - y1:y1 - y2; | ||
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| + | delta_x <<= 1; | ||
| + | delta_y <<= 1; | ||
plot(x1, y1); | plot(x1, y1); | ||
Revision as of 20:16, 26 April 2010
C++
Here's a C++ version; plot() draws a "dot" at (x, y):
//////////////////////////////////////////////////////////////////////////////// void Bresenham(int x1, int y1, int x2, int y2) { // 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; int delta_x = ix > 0?x2 - x1:x1 - x2; int delta_y = iy > 0?y2 - y1:y1 - y2; delta_x <<= 1; delta_y <<= 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); } } }
Ruby
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
