Merge pull request matplotlib#6602 from jenshnielsen/cairoimage

tacaswell · web-flow · commit 003dea9afa77 · 2016-06-20T17:30:20.000-04:00
Fix image plotting in Cairo backends
diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
@@ -68,6 +68,21 @@ def _fn_name(): return sys._getframe(1).f_code.co_name
     BYTE_FORMAT = 1 # ARGB
 
 
+class ArrayWrapper:
+    """Thin wrapper around numpy ndarray to expose the interface
+       expected by cairocffi. Basically replicates the
+       array.array interface.
+    """
+    def __init__(self, myarray):
+        self.__array = myarray
+        self.__data = myarray.ctypes.data
+        self.__size = len(myarray.flatten())
+        self.itemsize = myarray.itemsize
+
+    def buffer_info(self):
+        return (self.__data, self.__size)
+
+
 class RendererCairo(RendererBase):
     fontweights = {
         100          : cairo.FONT_WEIGHT_NORMAL,
@@ -175,9 +190,25 @@ def draw_image(self, gc, x, y, im):
             im = im[:, :, (2, 1, 0, 3)]
         else:
             im = im[:, :, (3, 0, 1, 2)]
-        surface = cairo.ImageSurface.create_for_data(
-            memoryview(im.flatten()), cairo.FORMAT_ARGB32, im.shape[1], im.shape[0],
-            im.shape[1]*4)
+        if HAS_CAIRO_CFFI:
+            # cairocffi tries to use the buffer_info from array.array
+            # that we replicate in ArrayWrapper and alternatively falls back
+            # on ctypes to get a pointer to the numpy array. This works
+            # correctly on a numpy array in python3 but not 2.7. We replicate
+            # the array.array functionality here to get cross version support.
+            imbuffer = ArrayWrapper(im.flatten())
+        else:
+            # py2cairo uses PyObject_AsWriteBuffer
+            # to get a pointer to the numpy array this works correctly
+            # on a regular numpy array but not on a memory view.
+            # At the time of writing the latest release version of
+            # py3cairo still does not support create_for_data
+            imbuffer = im.flatten()
+        surface = cairo.ImageSurface.create_for_data(imbuffer,
+                                                     cairo.FORMAT_ARGB32,
+                                                     im.shape[1],
+                                                     im.shape[0],
+                                                     im.shape[1]*4)
         ctx = gc.ctx
         y = self.height - y - im.shape[0]
 
