From 7e57660573abbe567a25434b7bdea07acbd9f365 Mon Sep 17 00:00:00 2001
From: Antony Lee <anntzer.lee@gmail.com>
Date: Thu, 21 May 2020 20:48:47 +0200
Subject: [PATCH] Add support for blitting in qt5cairo.

Test with e.g. examples/event_handling/poly_editor.py.

Doing the same for the other foocairo backends is left as an exercise to
the reader.
---
 lib/matplotlib/backends/backend_cairo.py  | 40 +++++++++++++++++++++++
 lib/matplotlib/backends/backend_qt5.py    |  9 +++++
 lib/matplotlib/backends/backend_qt5agg.py | 12 -------
 3 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/lib/matplotlib/backends/backend_cairo.py b/lib/matplotlib/backends/backend_cairo.py
index 240552423884..77f0b8abb6bc 100644
--- a/lib/matplotlib/backends/backend_cairo.py
+++ b/lib/matplotlib/backends/backend_cairo.py
@@ -7,6 +7,7 @@
 """
 
 import gzip
+import math
 
 import numpy as np
 
@@ -402,8 +403,47 @@ def set_linewidth(self, w):
         self.ctx.set_line_width(self.renderer.points_to_pixels(w))
 
 
+class _CairoRegion:
+    def __init__(self, slices, data):
+        self._slices = slices
+        self._data = data
+
+
 class FigureCanvasCairo(FigureCanvasBase):
 
+    def copy_from_bbox(self, bbox):
+        surface = self._renderer.gc.ctx.get_target()
+        if not isinstance(surface, cairo.ImageSurface):
+            raise RuntimeError(
+                "copy_from_bbox only works when rendering to an ImageSurface")
+        sw = surface.get_width()
+        sh = surface.get_height()
+        x0 = math.ceil(bbox.x0)
+        x1 = math.floor(bbox.x1)
+        y0 = math.ceil(sh - bbox.y1)
+        y1 = math.floor(sh - bbox.y0)
+        if not (0 <= x0 and x1 <= sw and bbox.x0 <= bbox.x1
+                and 0 <= y0 and y1 <= sh and bbox.y0 <= bbox.y1):
+            raise ValueError("Invalid bbox")
+        sls = slice(y0, y0 + max(y1 - y0, 0)), slice(x0, x0 + max(x1 - x0, 0))
+        data = (np.frombuffer(surface.get_data(), np.uint32)
+                .reshape((sh, sw))[sls].copy())
+        return _CairoRegion(sls, data)
+
+    def restore_region(self, region):
+        surface = self._renderer.gc.ctx.get_target()
+        if not isinstance(surface, cairo.ImageSurface):
+            raise RuntimeError(
+                "restore_region only works when rendering to an ImageSurface")
+        surface.flush()
+        sw = surface.get_width()
+        sh = surface.get_height()
+        sly, slx = region._slices
+        (np.frombuffer(surface.get_data(), np.uint32)
+         .reshape((sh, sw))[sly, slx]) = region._data
+        surface.mark_dirty_rectangle(
+            slx.start, sly.start, slx.stop - slx.start, sly.stop - sly.start)
+
     def print_png(self, fobj, *args, **kwargs):
         self._get_printed_image_surface().write_to_png(fobj)
 
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
index 104207d1f089..1ad56febd22a 100644
--- a/lib/matplotlib/backends/backend_qt5.py
+++ b/lib/matplotlib/backends/backend_qt5.py
@@ -460,6 +460,15 @@ def draw_idle(self):
             self._draw_pending = True
             QtCore.QTimer.singleShot(0, self._draw_idle)
 
+    def blit(self, bbox=None):
+        # docstring inherited
+        if bbox is None and self.figure:
+            bbox = self.figure.bbox  # Blit the entire canvas if bbox is None.
+        # repaint uses logical pixels, not physical pixels like the renderer.
+        l, b, w, h = [pt / self._dpi_ratio for pt in bbox.bounds]
+        t = b + h
+        self.repaint(l, self.rect().height() - t, w, h)
+
     def _draw_idle(self):
         with self._idle_draw_cntx():
             if not self._draw_pending:
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
index 6e90dc8a88ff..2d4d636d4018 100644
--- a/lib/matplotlib/backends/backend_qt5agg.py
+++ b/lib/matplotlib/backends/backend_qt5agg.py
@@ -78,18 +78,6 @@ def paintEvent(self, event):
 
         painter.end()
 
-    def blit(self, bbox=None):
-        # docstring inherited
-        # If bbox is None, blit the entire canvas. Otherwise
-        # blit only the area defined by the bbox.
-        if bbox is None and self.figure:
-            bbox = self.figure.bbox
-
-        # repaint uses logical pixels, not physical pixels like the renderer.
-        l, b, w, h = [pt / self._dpi_ratio for pt in bbox.bounds]
-        t = b + h
-        self.repaint(l, self.renderer.height / self._dpi_ratio - t, w, h)
-
     def print_figure(self, *args, **kwargs):
         super().print_figure(*args, **kwargs)
         self.draw()