:s/unmultiplied/straight.

ISSUES.rst

@@ -74,8 +74,8 @@ Matplotlib's draw_path_collection has inconsistent semantics across backends
 Issues with cairo
 -----------------
 
-Precision is lost when roundtripping between unmultiplied and premultiplied
-alpha. ::
+Precision is lost when roundtripping between straight and premultiplied alpha.
+::
 
    test_agg::test_repeated_save_with_alpha
 

README.rst

@@ -271,11 +271,11 @@ e.g. ``matplotlib.use("module://mplcairo.macosx")``.
 Alternatively, set the ``MPLCAIRO_PATCH_AGG`` environment variable to a
 non-empty value to fully replace the Agg renderer by the cairo renderer
 throughout Matplotlib.  However, this approach is inefficient (due to the need
-of copies and conversions between premultiplied ARGB32 and non-premultiplied
-RGBA8888 buffers); additionally, it does not work with the wx and macosx
-backends due to peculiarities of the corresponding canvas classes.  On the
-other hand, this is currently the only way in which the webagg-based backends
-(e.g., Jupyter's inline widget) are supported.
+of copies and conversions between premultiplied ARGB32 and straight RGBA8888
+buffers); additionally, it does not work with the wx and macosx backends due
+to peculiarities of the corresponding canvas classes.  On the other hand, this
+is currently the only way in which the webagg-based backends (e.g., Jupyter's
+inline widget) are supported.
 
 At import-time, mplcairo will attempt to load Raqm_.  The use of that library
 can be controlled and checked using the ``set_options`` and ``get_options``

lib/mplcairo/_util.py

@@ -12,10 +12,10 @@ def to_premultiplied_rgba8888(buf):
         [2, 1, 0, 3] if sys.byteorder == "little" else [1, 2, 3, 0], axis=2)
 
 
-def to_unmultiplied_rgba8888(buf):
-    """Convert a buffer from premultiplied ARGB32 to unmultiplied RGBA8888."""
+def to_straight_rgba8888(buf):
+    """Convert a buffer from premultiplied ARGB32 to straight RGBA8888."""
     rgba = to_premultiplied_rgba8888(buf)
-    # Un-premultiply alpha.  The formula is the same as in cairo-png.c.
+    # The straightening formula is from cairo-png.c.
     rgb = rgba[..., :-1]
     alpha = rgba[..., -1]
     mask = alpha != 0

lib/mplcairo/base.py

@@ -123,7 +123,7 @@ def draw_tex(self, gc, x, y, s, prop, angle, ismath="TeX!", mtext=None):
         mb._draw(self, x, y, angle)
 
     def stop_filter(self, filter_func):
-        img = _util.to_unmultiplied_rgba8888(self._stop_filter_get_buffer())
+        img = _util.to_straight_rgba8888(self._stop_filter_get_buffer())
         img, (l, b, w, h) = _get_drawn_subarray_and_bounds(img)
         if not (w and h):
             return
@@ -148,13 +148,13 @@ def stop_rasterizing(self):
     lock = _LOCK  # Needed for webagg_core; fixed by matplotlib#10708.
 
     def buffer_rgba(self):  # Needed for webagg_core.
-        return _util.to_unmultiplied_rgba8888(self._get_buffer())
+        return _util.to_straight_rgba8888(self._get_buffer())
 
     _renderer = property(buffer_rgba)  # Needed for tkagg.
 
     def tostring_rgba_minimized(self):  # Needed for MixedModeRenderer.
         img, bounds = _get_drawn_subarray_and_bounds(
-            _util.to_unmultiplied_rgba8888(self._get_buffer()))
+            _util.to_straight_rgba8888(self._get_buffer()))
         return img.tobytes(), bounds
 
 
@@ -272,22 +272,22 @@ def _print_ps_impl(self, is_eps, path_or_stream,
     print_ps = partialmethod(_print_ps_impl, False)
     print_eps = partialmethod(_print_ps_impl, True)
 
-    def _get_fresh_unmultiplied_rgba8888(self):
+    def _get_fresh_straight_rgba8888(self):
         # Swap out the cache, as savefig may be playing with the background
         # color.
         last_renderer_call = self._last_renderer_call
         self._last_renderer_call = (None, None)
         with _LOCK:
             renderer = self.get_renderer(_draw_if_new=True)
         self._last_renderer_call = last_renderer_call
-        return _util.to_unmultiplied_rgba8888(renderer._get_buffer())
+        return _util.to_straight_rgba8888(renderer._get_buffer())
 
     def print_rgba(
             self, path_or_stream, *, metadata=None,
             # These arguments are already taken care of by print_figure().
             dpi=72, facecolor=None, edgecolor=None, orientation="portrait",
             dryrun=False, bbox_inches_restore=None):
-        img = self._get_fresh_unmultiplied_rgba8888()
+        img = self._get_fresh_straight_rgba8888()
         if dryrun:
             return
         with cbook.open_file_cm(path_or_stream, "wb") as stream:
@@ -300,7 +300,7 @@ def print_png(
             # These arguments are already taken care of by print_figure().
             dpi=72, facecolor=None, edgecolor=None, orientation="portrait",
             dryrun=False, bbox_inches_restore=None):
-        img = self._get_fresh_unmultiplied_rgba8888()
+        img = self._get_fresh_straight_rgba8888()
         if dryrun:
             return
         full_metadata = OrderedDict(
@@ -320,13 +320,13 @@ def print_jpeg(
                 dryrun=False, bbox_inches_restore=None,
                 # Remaining kwargs are passed to PIL.
                 **kwargs):
-            buf = self._get_fresh_unmultiplied_rgba8888()
+            buf = self._get_fresh_straight_rgba8888()
             if dryrun:
                 return
             img = Image.frombuffer(
                 "RGBA", buf.shape[:2][::-1], buf, "raw", "RGBA", 0, 1)
             # Composite against the background (actually we could just skip the
-            # conversion to unpremultiplied RGBA earlier).
+            # conversion to straight RGBA earlier).
             # NOTE: Agg composites against rcParams["savefig.facecolor"].
             background = tuple(
                 (np.array(colors.to_rgb(facecolor)) * 255).astype(int))
@@ -343,7 +343,7 @@ def print_tiff(
                 # These arguments are already taken care of by print_figure().
                 dpi=72, facecolor=None, edgecolor=None, orientation="portrait",
                 dryrun=False, bbox_inches_restore=None):
-            buf = self._get_fresh_unmultiplied_rgba8888()
+            buf = self._get_fresh_straight_rgba8888()
             if dryrun:
                 return
             (Image.frombuffer(

lib/mplcairo/macosx.py

@@ -27,7 +27,7 @@ def __init__(self, figure):
     def _draw(self):
         if self.figure.stale:
             self._last_renderer_call = None, None
-        self._renderer = _util.to_unmultiplied_rgba8888(
+        self._renderer = _util.to_straight_rgba8888(
             self.get_renderer(_draw_if_new=True)._get_buffer())
         return self