First version

jsignature/utils.py

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+"""
+    Very inspired by zivezab's django-autograph
+    https://github.com/zivezab/django-autograph/blob/master/autograph/utils.py
+"""
+import json
+import cStringIO
+from itertools import chain
+from tempfile import NamedTemporaryFile
+from PIL import Image, ImageDraw, ImageOps
+
+AA = 5 # super sampling gor antialiasing
+
+def draw_signature(data, as_file=False):
+    """ Draw signature based on lines stored in json_string.
+        `data` can be a json object (list in fact) or a json string
+        if `as_file` is True, a temp file is returned instead of Image instance
+    """
+
+    if type(data) is str:
+        drawing = json.loads(data)
+    elif type(data) is list:
+        drawing = data
+    else:
+        raise ValueError
+
+    # Compute box
+    width = max(chain(*[d['x'] for d in data])) + 10
+    height = max(chain(*[d['y'] for d in data])) + 10
+
+    # Draw image
+    im = Image.new("RGBA", (width*AA, height*AA))
+    draw = ImageDraw.Draw(im)
+    for line in drawing:
+        len_line = len(line['x'])
+        points = [(line['x'][i]*AA, line['y'][i]*AA) for i in range(0, len_line)]
+        draw.line(points, fill="#000", width=2*AA)
+    im = ImageOps.expand(im)
+    # Smart crop
+    bbox = im.getbbox()
+    if bbox:
+        im.crop(bbox)
+
+    im.thumbnail((width, height), Image.ANTIALIAS)
+
+    if as_file:
+        ret = im._dump(format='PNG')
+    else:
+        ret = img
+
+    return ret
+