78 lines
2.1 KiB
Python
78 lines
2.1 KiB
Python
"""Script demonstrating drawing of anti-aliased lines using Xiaolin Wu's line
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algorithm
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usage: python xiaolinwu.py [output-file]
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"""
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from __future__ import division
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import sys
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from PIL import Image
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def _fpart(x):
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return x - int(x)
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def _rfpart(x):
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return 1 - _fpart(x)
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def putpixel(img, xy, color, alpha=1):
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"""
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Paints color over the background at the point xy in img.
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Use alpha for blending. alpha=1 means a completely opaque foreground.
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"""
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compose_color = lambda bg, fg: int(round(alpha * fg + (1-alpha) * bg))
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c = compose_color(img.getpixel(xy), color)
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img.putpixel(xy, c)
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def draw_line(img, p1, p2, color):
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"""Draws an anti-aliased line in img from p1 to p2 with the given color."""
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x1, y1 = p1
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x2, y2 = p2
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dx, dy = x2-x1, y2-y1
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steep = abs(dx) < abs(dy)
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p = lambda px, py: ((px,py), (py,px))[steep]
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if steep:
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x1, y1, x2, y2, dx, dy = y1, x1, y2, x2, dy, dx
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if x2 < x1:
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x1, x2, y1, y2 = x2, x1, y2, y1
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grad = dy/dx
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intery = y1 + _rfpart(x1) * grad
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def draw_endpoint(pt):
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x, y = pt
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xend = round(x)
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yend = y + grad * (xend - x)
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xgap = _rfpart(x + 0.5)
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px, py = int(xend), int(yend)
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putpixel(img, p(px, py), color, _rfpart(yend) * xgap)
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putpixel(img, p(px, py+1), color, _fpart(yend) * xgap)
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return px
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xstart = draw_endpoint(p(*p1)) + 1
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xend = draw_endpoint(p(*p2))
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for x in range(xstart, xend):
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y = int(intery)
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putpixel(img, p(x, y), color, _rfpart(intery))
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putpixel(img, p(x, y+1), color, _fpart(intery))
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intery += grad
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if __name__ == '__main__':
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if len(sys.argv) != 2:
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print 'usage: python xiaolinwu.py [output-file]'
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sys.exit(-1)
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blue = (0, 0, 255)
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yellow = (255, 255, 0)
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img = Image.new("RGB", (500,500), blue)
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for a in range(10, 431, 60):
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draw_line(img, (10, 10), (490, a), yellow)
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draw_line(img, (10, 10), (a, 490), yellow)
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draw_line(img, (10, 10), (490, 490), yellow)
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filename = sys.argv[1]
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img.save(filename)
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print 'image saved to', filename
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