Initial data commit

Task/Xiaolin-Wus-line-algorithm/Python/xiaolin-wus-line-algorithm.py

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