Add drawing module with Bresenham line.

CONTRIBUTORS.txt

@@ -70,3 +70,6 @@
 
 - Brian Holt
   Histograms of Oriented Gradients
+
+- David-Warde Farley, Sturla Molden
+  Bresenheim line drawing, from snippets on numpy-discussion.

TASKS.txt

@@ -122,3 +122,7 @@ Implement Algorithms
 - Graph cut segmentation
 - Probabilistic Hough transform
 
+Drawing
+```````
+- Wu's algorithm for lines and circles
+

scikits/image/draw/__init__.py

@@ -0,0 +1 @@
+from draw import *

scikits/image/draw/_draw.pyx

@@ -0,0 +1,66 @@
+import numpy as np
+cimport numpy as np
+cimport cython
+
+cdef extern from "math.h":
+    int abs(int i)
+
+@cython.boundscheck(False)
+@cython.wraparound(False)
+def bresenham(int y, int x, int y2, int x2):
+    """
+    Generate line pixel coordinates.
+    
+    Parameters
+    ----------
+    y, x : int
+        Starting position (row, column).
+    y2, x2 : int
+        End position (row, column).
+
+    Returns
+    -------
+    rr, cc : (N,) ndarray of int
+        Indices of pixels that belong to the line.
+        May be used to directly index into an array, e.g.
+        ``img[rr, cc] = 1``.
+
+    """
+    cdef np.ndarray[np.int32_t, ndim=1, mode="c"] rr, cc
+
+    cdef int steep = 0
+    cdef int dx = abs(x2 - x)
+    cdef int dy = abs(y2 - y)
+    cdef int sx, sy, d, i
+
+    if (x2 - x) > 0: sx = 1
+    else: sx = -1
+    if (y2 - y) > 0: sy = 1
+    else: sy = -1
+    if dy > dx:
+        steep = 1
+        x,y = y,x
+        dx,dy = dy,dx
+        sx,sy = sy,sx
+    d = (2 * dy) - dx
+
+    rr = np.zeros(int(dx) + 1, dtype=np.int32)
+    cc = np.zeros(int(dx) + 1, dtype=np.int32)
+    
+    for i in range(dx):
+        if steep:
+            rr[i] = x
+            cc[i] = y
+        else:
+            rr[i] = y
+            cc[i] = x
+        while d >= 0:
+            y = y + sy
+            d = d - (2 * dx)
+        x = x + sx
+        d = d + (2 * dy)
+
+    rr[dx] = y2
+    cc[dx] = x2
+
+    return rr, cc

scikits/image/draw/draw.py

@@ -0,0 +1,6 @@
+"""
+Methods to draw on arrays.
+
+"""
+
+from _draw import bresenham

scikits/image/draw/setup.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+
+import os
+from scikits.image._build import cython
+
+base_path = os.path.abspath(os.path.dirname(__file__))
+
+def configuration(parent_package='', top_path=None):
+    from numpy.distutils.misc_util import Configuration, get_numpy_include_dirs
+
+    config = Configuration('draw', parent_package, top_path)
+    config.add_data_dir('tests')
+
+    cython(['_draw.pyx'], working_path=base_path)
+
+    config.add_extension('_draw', sources=['_draw.c'],
+                         include_dirs=[get_numpy_include_dirs()])
+
+    return config
+
+if __name__ == '__main__':
+    from numpy.distutils.core import setup
+    setup(maintainer = 'Scikits-image developers',
+          author = 'Scikits-image developers',
+          maintainer_email = 'scikits-image@googlegroups.com',
+          description = 'Drawing',
+          url = 'https://github.com/scikits-image/scikits.image',
+          license = 'SciPy License (BSD Style)',
+          **(configuration(top_path='').todict())
+          )

scikits/image/draw/tests/test_draw.py

@@ -0,0 +1,52 @@
+from numpy.testing import assert_array_equal
+import numpy as np
+
+from scikits.image.draw import bresenham
+
+def test_bresenham_horizontal():
+    img = np.zeros((10, 10))
+
+    rr, cc = bresenham(0, 0, 0, 9)
+    img[rr, cc] = 1
+
+    img_ = np.zeros((10, 10))
+    img_[0, :] = 1
+
+    assert_array_equal(img, img_)
+
+def test_bresenham_vertical():
+    img = np.zeros((10, 10))
+
+    rr, cc = bresenham(0, 0, 9, 0)
+    img[rr, cc] = 1
+
+    img_ = np.zeros((10, 10))
+    img_[:, 0] = 1
+
+    assert_array_equal(img, img_)
+
+def test_reverse():
+    img = np.zeros((10, 10))
+
+    rr, cc = bresenham(0, 9, 0, 0)
+    img[rr, cc] = 1
+
+    img_ = np.zeros((10, 10))
+    img_[0, :] = 1
+
+    assert_array_equal(img, img_)
+
+def test_diag():
+    img = np.zeros((5, 5))
+
+    rr, cc = bresenham(0, 0, 4, 4)
+    img[rr, cc] = 1
+
+    img_ = np.eye(5)
+
+    assert_array_equal(img, img_)
+
+
+if __name__ == "__main__":
+    from numpy.testing import run_module_suite
+