From ab61cbe79cd2350e2fd082aa44adac195d7f7b69 Mon Sep 17 00:00:00 2001
From: Elliott Sales de Andrade <quantum.analyst@gmail.com>
Date: Fri, 15 Oct 2021 00:44:51 -0400
Subject: [PATCH] Convert macosx backend to use device_pixel_ratio

This was not originally implemented in #19126, but causes some
inconsistencies with other backends.

This also sets the initial scale as implemented in #18274.
---
 lib/matplotlib/backends/backend_macosx.py | 19 +++-------
 src/_macosx.m                             | 42 ++++++++++++++++++-----
 2 files changed, 38 insertions(+), 23 deletions(-)

diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
index a692504afb23..25619104134f 100644
--- a/lib/matplotlib/backends/backend_macosx.py
+++ b/lib/matplotlib/backends/backend_macosx.py
@@ -30,14 +30,6 @@ def __init__(self, figure):
         FigureCanvasBase.__init__(self, figure)
         width, height = self.get_width_height()
         _macosx.FigureCanvas.__init__(self, width, height)
-        self._dpi_ratio = 1.0
-
-    def _set_device_scale(self, value):
-        if self._dpi_ratio != value:
-            # Need the new value in place before setting figure.dpi, which
-            # will trigger a resize
-            self._dpi_ratio, old_value = value, self._dpi_ratio
-            self.figure.dpi = self.figure.dpi / old_value * self._dpi_ratio
 
     def set_cursor(self, cursor):
         # docstring inherited
@@ -60,12 +52,11 @@ def blit(self, bbox=None):
         self.draw_idle()
 
     def resize(self, width, height):
-        dpi = self.figure.dpi
-        width /= dpi
-        height /= dpi
-        self.figure.set_size_inches(width * self._dpi_ratio,
-                                    height * self._dpi_ratio,
-                                    forward=False)
+        # Size from macOS is logical pixels, dpi is physical.
+        scale = self.figure.dpi / self.device_pixel_ratio
+        width /= scale
+        height /= scale
+        self.figure.set_size_inches(width, height, forward=False)
         FigureCanvasBase.resize_event(self)
         self.draw_idle()
 
diff --git a/src/_macosx.m b/src/_macosx.m
index ef999ca9ea2d..9eeeab46eb5b 100755
--- a/src/_macosx.m
+++ b/src/_macosx.m
@@ -237,6 +237,8 @@ @interface View : NSView <NSWindowDelegate>
 }
 - (void)dealloc;
 - (void)drawRect:(NSRect)rect;
+- (void)updateDevicePixelRatio:(double)scale;
+- (void)windowDidChangeBackingProperties:(NSNotification*)notification;
 - (void)windowDidResize:(NSNotification*)notification;
 - (View*)initWithFrame:(NSRect)rect;
 - (void)setCanvas: (PyObject*)newCanvas;
@@ -706,6 +708,7 @@ static CGFloat _get_device_scale(CGContextRef cr)
     [window setDelegate: view];
     [window makeFirstResponder: view];
     [[window contentView] addSubview: view];
+    [view updateDevicePixelRatio: [window backingScaleFactor]];
 
     return 0;
 }
@@ -801,6 +804,9 @@ static CGFloat _get_device_scale(CGContextRef cr)
     Window* window = self->window;
     if(window)
     {
+        CGFloat device_pixel_ratio = [window backingScaleFactor];
+        width /= device_pixel_ratio;
+        height /= device_pixel_ratio;
         // 36 comes from hard-coded size of toolbar later in code
         [window setContentSize: NSMakeSize(width, height + 36.)];
     }
@@ -1654,15 +1660,6 @@ -(void)drawRect:(NSRect)rect
 
     CGContextRef cr = [[NSGraphicsContext currentContext] CGContext];
 
-    double new_device_scale = _get_device_scale(cr);
-
-    if (device_scale != new_device_scale) {
-        device_scale = new_device_scale;
-        if (!PyObject_CallMethod(canvas, "_set_device_scale", "d", device_scale, NULL)) {
-            PyErr_Print();
-            goto exit;
-        }
-    }
     if (!(renderer = PyObject_CallMethod(canvas, "_draw", "", NULL))
         || !(renderer_buffer = PyObject_GetAttrString(renderer, "_renderer"))) {
         PyErr_Print();
@@ -1683,6 +1680,33 @@ -(void)drawRect:(NSRect)rect
     PyGILState_Release(gstate);
 }
 
+- (void)updateDevicePixelRatio:(double)scale
+{
+    PyObject* change = NULL;
+    PyGILState_STATE gstate = PyGILState_Ensure();
+
+    device_scale = scale;
+    if (!(change = PyObject_CallMethod(canvas, "_set_device_pixel_ratio", "d", device_scale, NULL))) {
+        PyErr_Print();
+        goto exit;
+    }
+    if (PyObject_IsTrue(change)) {
+        [self setNeedsDisplay: YES];
+    }
+
+  exit:
+    Py_XDECREF(change);
+
+    PyGILState_Release(gstate);
+}
+
+- (void)windowDidChangeBackingProperties:(NSNotification *)notification
+{
+    Window* window = [notification object];
+
+    [self updateDevicePixelRatio: [window backingScaleFactor]];
+}
+
 - (void)windowDidResize: (NSNotification*)notification
 {
     int width, height;

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