compute image difference & update reference images

tests/visual_tests/shieldsymbolizer-1.xml

@@ -12,7 +12,7 @@
 
     <Style name="My Style">
     <Rule>
-      <ShieldSymbolizer face-name="DejaVu Sans Book" size="16" placement="point" file="../data/svg/rect.svg" dx="0" dy="-5">'x'</ShieldSymbolizer>
+      <ShieldSymbolizer face-name="DejaVu Sans Book" size="16" placement="point" file="../data/svg/rect.svg">'x'</ShieldSymbolizer>
     </Rule>
   </Style>
 

tests/visual_tests/test.py

@@ -5,6 +5,8 @@ import mapnik
 import cairo
 import sys
 import os.path
+import math, operator
+import Image
 
 dirname = os.path.dirname(sys.argv[0])
 
@@ -14,14 +16,45 @@ filenames_one_width = ["simple-E", "simple-NE", "simple-NW", "simple-N",
     "simple-SE", "simple-SW", "simple-S", "simple-W",
     "formating-1", "formating-2", "formating-3", "formating-4",
     "shieldsymbolizer-1", "expressionformat"]
-    
+
+COMPUTE_THRESHOLD = 0
+
+# returns true if pixels are not identical
+def compare_pixels(pixel1, pixel2):
+    r_diff = abs(pixel1[0] - pixel2[0])
+    g_diff = abs(pixel1[1] - pixel2[1])
+    b_diff = abs(pixel1[2] - pixel2[2])
+    if(r_diff > COMPUTE_THRESHOLD or g_diff > COMPUTE_THRESHOLD or b_diff > COMPUTE_THRESHOLD):
+        return True
+    else:
+        return False
+
+# compare tow images and return number of different pixels
+def compare(im1, im2):
+    diff = 0
+    pixels = im1.size[0] * im1.size[1]
+    im1 = im1.getdata()
+    im2 = im2.getdata()
+    for i in range(3, pixels - 1, 3):
+        if(compare_pixels(im1[i], im2[i])):
+            diff = diff + 1
+    return diff
+
 def render(filename, width):
-    print "Rendering style \"%s\" with width %d" % (filename, width)
     m = mapnik.Map(width, 100)
     mapnik.load_map(m, os.path.join(dirname, "%s.xml" % filename), False)
     bbox = mapnik.Box2d(-0.05, -0.01, 0.95, 0.01)
     m.zoom_to_box(bbox)
     mapnik.render_to_file(m, '%s-%d-agg.png' % (filename, width))
+    im1 = Image.open('%s-%d-reference.png' % (filename, width))
+    im2 = Image.open('%s-%d-agg.png' % (filename, width))
+    diff = compare(im1, im2)
+    if diff == 0:
+        rms = 'ok'
+    else:
+        rms = 'error: %u different pixels' % diff
+
+    print "Rendering style \"%s\" with width %d ... %s" % (filename, width, rms)
     return m
     
 if len(sys.argv) > 1: