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Fix gtk3agg alpha channel. #10297

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Merged
merged 1 commit into from
Jul 1, 2018
Merged

Fix gtk3agg alpha channel. #10297

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28 changes: 21 additions & 7 deletions lib/matplotlib/backends/backend_gtk3agg.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
import numpy as np
import sys
import warnings

import numpy as np

from . import backend_agg, backend_cairo, backend_gtk3
from ._gtk3_compat import gi
from .backend_cairo import cairo
Expand Down Expand Up @@ -31,7 +33,7 @@ def _render_figure(self, width, height):
backend_agg.FigureCanvasAgg.draw(self)

def on_draw_event(self, widget, ctx):
""" GtkDrawable draw event, like expose_event in GTK 2.X
"""GtkDrawable draw event, like expose_event in GTK 2.X.
"""
allocation = self.get_allocation()
w, h = allocation.width, allocation.height
Expand All @@ -45,17 +47,29 @@ def on_draw_event(self, widget, ctx):
ctx = backend_cairo._to_context(ctx)

for bbox in bbox_queue:
area = self.copy_from_bbox(bbox)
buf = np.fromstring(area.to_string_argb(), dtype='uint8')

x = int(bbox.x0)
y = h - int(bbox.y1)
width = int(bbox.x1) - int(bbox.x0)
height = int(bbox.y1) - int(bbox.y0)

buf = (np.fromstring(self.copy_from_bbox(bbox).to_string_argb(),
dtype='uint8')
.reshape((width, height, 4)))
# cairo wants premultiplied alpha. Only bother doing the
# conversion when the alpha channel is not fully opaque, as the
# cost is not negligible. (The unsafe cast is needed to do the
# multiplication in-place in an integer buffer.)
if sys.byteorder == "little":
rgb24 = buf[..., :-1]
alpha8 = buf[..., -1:]
else:
alpha8 = buf[..., :1]
rgb24 = buf[..., 1:]
if alpha8.min() != 0xff:
np.multiply(rgb24, alpha8 / 0xff, out=rgb24, casting="unsafe")

image = cairo.ImageSurface.create_for_data(
buf.ravel().data, cairo.FORMAT_ARGB32,
width, height, width * 4)
buf.ravel().data, cairo.FORMAT_ARGB32, width, height)
ctx.set_source_surface(image, x, y)
ctx.paint()

Expand Down