Dec 15, 2020 · Dec 3, 2020 · Dec 3, 2020 · Dec 3, 2020 · Dec 4, 2020 · Dec 5, 2020
diff --git a/lib/matplotlib/backends/backend_webagg_core.py b/lib/matplotlib/backends/backend_webagg_core.py


 class FigureCanvasWebAggCore(backend_agg.FigureCanvasAgg):
    supports_blit =False
    supports_blit =True

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        finally:
            self.manager.refresh_all()  # Swap the frames.

    def blit(self, bbox=None):
        self._png_is_old = True
        self.manager.refresh_all()

    def draw_idle(self):
        self.send_event("draw")

                output = buff
            else:
                self.set_image_mode('diff')
                last_buffer = (np.frombuffer(self._last_renderer.buffer_rgba(),
                                             dtype=np.uint32)
                               .reshape((renderer.height, renderer.width)))
                diff = buff != last_buffer
                diff = buff != self._last_buff
                output = np.where(diff, buff, 0)

            buf = BytesIO()
            data = output.view(dtype=np.uint8).reshape((*output.shape, 4))
            Image.fromarray(data).save(buf, format="png")
            # Swap the renderer frames
            self._renderer, self._last_renderer = (
                self._last_renderer, renderer)
            # store the current buffer so we can compute the next diff
            np.copyto(self._last_buff, buff)
            self._force_full = False
            self._png_is_old = False
            return buf.getvalue()
        if need_new_renderer:
            self._renderer = backend_agg.RendererAgg(
                w, h, self.figure.dpi)
            self._last_renderer = backend_agg.RendererAgg(
                w, h, self.figure.dpi)
            self._lastKey = key
            self._last_buff = np.copy(np.frombuffer(
                self._renderer.buffer_rgba(), dtype=np.uint32
            ).reshape((self._renderer.height, self._renderer.width)))

        elif cleared:
            self._renderer.clear()
Original file line number	Diff line number	Diff line change
Expand Up		@@ -118,7 +118,7 @@ def _handle_key(key):


		class FigureCanvasWebAggCore(backend_agg.FigureCanvasAgg):
		supports_blit =False
		supports_blit =True

		def __init__(self, args, *kwargs):
		super().__init__(args, *kwargs)
Expand DownExpand Up		@@ -153,6 +153,10 @@ def draw(self):
		finally:
		self.manager.refresh_all() # Swap the frames.

		def blit(self, bbox=None):
		self._png_is_old = True
		self.manager.refresh_all()
Comment on lines +156 to +158 Copy link ContributorAuthor ianhiDec 3, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I copied this from#4290 so I assume it was done correctly by@tacaswell, but I find it odd that this accepts a`bbox` argument but doesn't do anything with it. Is that a mistake? Copy link Member QuLogicDec 4, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. That's to match the super class; it should blit only the section in the bbox if it's not`None`. Just re-blitting everything is fine, but perhaps a bit under-optimized. I think you would have to add to the current wire protocol to be able to do bbox'd blitting. Copy link ContributorAuthor ianhiDec 5, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. makes sense. Should a docstring be added explaining something to that effect? Copy link ContributorAuthor ianhiDec 5, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I think I see how to implement more selective blitting for the ipympl frontend, but would/can the backend Agg renderer also needing blitting? Copy link ContributorAuthor ianhiDec 5, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. The other consideration is that if any part of the image is transparent it will be forced to be a full image. That could also be optimized a bit with frontend blitting. Discussed far in the past here:#5419 (comment) Copy link Member QuLogicDec 9, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I'm sure it could be possible, but would require sending a different message probably. Doesn't have to be done in this PR though. Copy link ContributorAuthor ianhiDec 9, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Indeed I'm happy with this PR as is. Better blitting seems like a good 2021 goal.

		def draw_idle(self):
		self.send_event("draw")

Expand DownExpand Up		@@ -189,18 +193,14 @@ def get_diff_image(self):
		output = buff
		else:
		self.set_image_mode('diff')
		last_buffer = (np.frombuffer(self._last_renderer.buffer_rgba(),
		dtype=np.uint32)
		.reshape((renderer.height, renderer.width)))
		diff = buff != last_buffer
		diff = buff != self._last_buff
		output = np.where(diff, buff, 0)

		buf = BytesIO()
Copy link thomasaarholtDec 3, 2020• edited Loading Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I notice that there are both`buff` and`buf` in this code (I realise you didn't introduce or touch the last one). Do you think you could attempt to clear up what the difference between them is, and perhaps make the variable names self explanatory? Making it clearer now will make it easier for the next developer who looks at this to understand what's going on :) Copy link ContributorAuthor ianhiDec 5, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. I haven't left a comment because I'm not 100% sure this is the reason. But here's the idea of what I might leave: We differentiate between`buff` and`buf` because we cannot directly return`buff` as that is a reference to a location in memory that may change later. There may also be something happening with the save where the buffer gets converted from whatever the renderer uses into a png buffer. Copy link Member QuLogicDec 15, 2020 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. See#19117. thomasaarholt reacted with hooray emoji
		data = output.view(dtype=np.uint8).reshape((*output.shape, 4))
		Image.fromarray(data).save(buf, format="png")
		# Swap the renderer frames
		self._renderer, self._last_renderer = (
		self._last_renderer, renderer)
		# store the current buffer so we can compute the next diff
		np.copyto(self._last_buff, buff)
		self._force_full = False
		self._png_is_old = False
		return buf.getvalue()
Expand All		@@ -220,9 +220,10 @@ def get_renderer(self, cleared=None):
		if need_new_renderer:
		self._renderer = backend_agg.RendererAgg(
		w, h, self.figure.dpi)
		self._last_renderer = backend_agg.RendererAgg(
		w, h, self.figure.dpi)
		self._lastKey = key
		self._last_buff = np.copy(np.frombuffer(
		self._renderer.buffer_rgba(), dtype=np.uint32
		).reshape((self._renderer.height, self._renderer.width)))

		elif cleared:
		self._renderer.clear()
Expand Down