Added the new set_alpha and multiply_alpha methods on image, also added tests for each

Author: flippmoke

setup.py

@@ -81,7 +81,7 @@
     if create_paths:
         f_paths.write('mapniklibpath = os.path.join(os.path.dirname(os.path.realpath(__file__)), "plugins")\n')
 elif create_paths:
-    f_paths.write("mapniklibpath = '"+lib_path+"/mapnik/plugins'\n")
+    f_paths.write("mapniklibpath = '"+lib_path+"/mapnik'\n")
     f_paths.write('mapniklibpath = os.path.normpath(mapniklibpath)\n')
 
 if create_paths:

src/mapnik_image.cpp

@@ -287,6 +287,11 @@ void set_alpha(image_any & im, float opacity)
     mapnik::set_alpha(im, opacity);
 }
 
+void multiply_alpha(image_any & im, float opacity)
+{
+    mapnik::multiply_alpha(im, opacity);
+}
+
 bool premultiplied(image_any &im)
 {
     return im.get_premultiplied();
@@ -406,6 +411,7 @@ void export_image()
         .def("set_grayscale_to_alpha",&set_grayscale_to_alpha_c, "Set the grayscale values to the alpha channel of the Image")
         .def("set_color_to_alpha",&set_color_to_alpha, "Set a given color to the alpha channel of the Image")
         .def("set_alpha",&set_alpha, "Set the overall alpha channel of the Image")
+        .def("multiply_alpha",&multiply_alpha, "Multiply the alpha channel of the Image")
         .def("composite",&composite,
          ( arg("self"),
            arg("image"),

test/python_tests/compositing_test.py

@@ -208,7 +208,7 @@ def test_rounding_and_color_expectations():
     # should have no effect
     im_file.premultiply()
     eq_(get_unique_colors(im_file),['rgba(0,0,0,0)', 'rgba(74,74,74,255)'])
-    im_file.set_alpha(.5)
+    im_file.multiply_alpha(.5)
     # should have effect now that image has transparency
     im_file.premultiply()
     eq_(get_unique_colors(im_file),['rgba(0,0,0,0)', 'rgba(37,37,37,127)'])

test/python_tests/image_test.py

@@ -49,6 +49,26 @@ def test_image_premultiply_values():
     eq_(c.b,255)
     eq_(c.a,128)
 
+def test_set_alpha():
+    im = mapnik.Image(4,4)
+    im.fill(mapnik.Color(128,128,128,128))
+    im.set_alpha(0.75);
+    c = im.get_pixel(0,0,True)
+    eq_(c.r,128)
+    eq_(c.g,128)
+    eq_(c.b,128)
+    eq_(c.a,191)
+
+def test_multiply_alpha():
+    im = mapnik.Image(4,4)
+    im.fill(mapnik.Color(128,128,128,128))
+    im.multiply_alpha(0.75);
+    c = im.get_pixel(0,0,True)
+    eq_(c.r,128)
+    eq_(c.g,128)
+    eq_(c.b,128)
+    eq_(c.a,96)
+
 def test_background():
     im = mapnik.Image(256,256)
     eq_(im.premultiplied(), False)

test/python_tests/render_test.py

@@ -67,7 +67,7 @@ def test_setting_alpha():
     im2 = mapnik.Image(w,h)
     c2 = mapnik.Color('rgba(255,255,255,1)')
     im2.fill(c2)
-    im2.set_alpha(c1.a/255.0)
+    im2.multiply_alpha(c1.a/255.0)
     eq_(im2.painted(),False)
     eq_(im2.is_solid(),True)
     eq_(len(im1.tostring('png32')), len(im2.tostring('png32')))