Correct image scaling on GTK

android/tests_backend/widgets/imageview.py

@@ -9,3 +9,8 @@ class ImageViewProbe(SimpleProbe):
     @property
     def preserve_aspect_ratio(self):
         return self.native.getScaleType() == ImageView.ScaleType.FIT_CENTER
+
+    def assert_image_size(self, width, height):
+        # Android internally scales the image to the container,
+        # so there's no image size check required.
+        pass

changes/2119.misc.rst

@@ -0,0 +1 @@
+An issue with imageview scaling on GTK was resolved.

cocoa/tests_backend/widgets/imageview.py

@@ -9,3 +9,8 @@ class ImageViewProbe(SimpleProbe):
     @property
     def preserve_aspect_ratio(self):
         return self.native.imageScaling == NSImageScaleProportionallyUpOrDown
+
+    def assert_image_size(self, width, height):
+        # Cocoa internally scales the image to the container,
+        # so there's no image size check required.
+        pass

gtk/src/toga_gtk/widgets/imageview.py

@@ -7,49 +7,51 @@
 class ImageView(Widget):
     def create(self):
         self.native = Gtk.Image()
+        self.native.connect("size-allocate", self.gtk_size_allocate)
         self._aspect_ratio = None
 
     def set_image(self, image):
         if image:
-            self.native.set_from_pixbuf(image._impl.native)
+            self.set_scaled_pixbuf(image._impl.native, self.native.get_allocation())
         else:
             self.native.set_from_pixbuf(None)
 
-    def set_bounds(self, x, y, width, height):
-        super().set_bounds(x, y, width, height)
-
-        # GTK doesn't have any native image resizing; we need to manually
-        # scale the native pixbuf to the preferred size as a result of
-        # resizing the image.
+    def gtk_size_allocate(self, widget, allocation):
+        # GTK doesn't have any native image resizing; so, when the Gtk.Image
+        # has a new size allocated, we need to manually scale the native pixbuf
+        # to the preferred size as a result of resizing the image.
         if self.interface.image:
-            if self._aspect_ratio is None:
-                # Don't preserve aspect ratio; image fits the available space.
-                image_width = width
-                image_height = height
+            self.set_scaled_pixbuf(self.interface.image._impl.native, allocation)
+
+    def set_scaled_pixbuf(self, image, allocation):
+        if self._aspect_ratio is None:
+            # Don't preserve aspect ratio; image fits the available space.
+            image_width = allocation.width
+            image_height = allocation.height
+        else:
+            # Determine what the width/height of the image would be
+            # preserving the aspect ratio. If the scaled size exceeds
+            # the allocated size, then that isn't the dimension
+            # being preserved.
+            candidate_width = int(allocation.height * self._aspect_ratio)
+            candidate_height = int(allocation.width / self._aspect_ratio)
+            if candidate_width > allocation.width:
+                image_width = allocation.width
+                image_height = candidate_height
             else:
-                # Determine what the width/height of the image would be
-                # preserving the aspect ratio. If the scaled size exceeds
-                # the allocated size, then that isn't the dimension
-                # being preserved.
-                candidate_width = int(height * self._aspect_ratio)
-                candidate_height = int(width / self._aspect_ratio)
-                if candidate_width > width:
-                    image_width = width
-                    image_height = candidate_height
-                else:
-                    image_width = candidate_width
-                    image_height = height
-
-            # Minimum image size is 1x1
-            image_width = max(1, image_width)
-            image_height = max(1, image_height)
-
-            # Scale the pixbuf to fit the provided space.
-            scaled = self.interface.image._impl.native.scale_simple(
-                image_width, image_height, GdkPixbuf.InterpType.BILINEAR
-            )
-
-            self.native.set_from_pixbuf(scaled)
+                image_width = candidate_width
+                image_height = allocation.height
+
+        # Minimum image size is 1x1
+        image_width = max(1, image_width)
+        image_height = max(1, image_height)
+
+        # Scale the pixbuf to fit the provided space.
+        scaled = self.interface.image._impl.native.scale_simple(
+            image_width, image_height, GdkPixbuf.InterpType.BILINEAR
+        )
+
+        self.native.set_from_pixbuf(scaled)
 
     def rehint(self):
         width, height, self._aspect_ratio = rehint_imageview(

gtk/tests_backend/widgets/imageview.py

@@ -9,3 +9,8 @@ class ImageViewProbe(SimpleProbe):
     @property
     def preserve_aspect_ratio(self):
         return self.impl._aspect_ratio is not None
+
+    def assert_image_size(self, width, height):
+        # Confirm the underlying pixelbuf has been scaled to the appropriate size.
+        pixbuf = self.native.get_pixbuf()
+        assert (pixbuf.get_width(), pixbuf.get_height()) == (width, height)

iOS/tests_backend/widgets/imageview.py

@@ -9,3 +9,8 @@ class ImageViewProbe(SimpleProbe):
     @property
     def preserve_aspect_ratio(self):
         return self.native.contentMode == UIViewContentMode.ScaleAspectFit.value
+
+    def assert_image_size(self, width, height):
+        # UIKit internally scales the image to the container,
+        # so there's no image size check required.
+        pass

testbed/tests/widgets/test_imageview.py

@@ -24,6 +24,7 @@ async def test_implicit_size(widget, probe, container_probe):
     assert probe.width == pytest.approx(144, abs=2)
     assert probe.height == pytest.approx(72, abs=2)
     assert probe.preserve_aspect_ratio
+    probe.assert_image_size(144, 72)
 
     # Clear the image; it's now an explicit sized empty image.
     widget.image = None
@@ -34,6 +35,7 @@ async def test_implicit_size(widget, probe, container_probe):
     assert not probe.preserve_aspect_ratio
 
     # Restore the image; Make the parent a flex row
+    # Image will become as wide as the container.
     widget.image = "resources/sample.png"
     widget.style.flex = 1
     widget.parent.style.direction = ROW
@@ -42,25 +44,36 @@ async def test_implicit_size(widget, probe, container_probe):
     assert probe.width == pytest.approx(container_probe.width, abs=2)
     assert probe.height == pytest.approx(container_probe.height, abs=2)
     assert probe.preserve_aspect_ratio
+    probe.assert_image_size(
+        pytest.approx(probe.width, abs=2),
+        pytest.approx(probe.width // 2, abs=2),
+    )
 
     # Make the parent a flex column
+    # Image will try to be as tall as the container, but will be
+    # constrained by preserving the aspect ratio
     widget.parent.style.direction = COLUMN
 
     await probe.redraw("Image is in a column box")
     assert probe.width == pytest.approx(container_probe.width, abs=2)
     assert probe.height == pytest.approx(container_probe.height, abs=2)
     assert probe.preserve_aspect_ratio
+    probe.assert_image_size(
+        pytest.approx(probe.width, abs=2),
+        pytest.approx(probe.width // 2, abs=2),
+    )
 
 
 async def test_explicit_width(widget, probe, container_probe):
     """If the image width is explicit, the image view will resize preserving aspect ratio."""
-    # Explicitly set width
+    # Explicitly set width; height follows aspect raio
     widget.style.width = 200
 
     await probe.redraw("Image has explicit width")
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(100, abs=2)
     assert probe.preserve_aspect_ratio
+    probe.assert_image_size(200, 100)
 
     # Clear the image; it's now an explicit sized empty image.
     widget.image = None
@@ -79,6 +92,8 @@ async def test_explicit_width(widget, probe, container_probe):
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(container_probe.height, abs=2)
     assert probe.preserve_aspect_ratio
+    # Container has fixed width; aspect ratio is preserved, so image isn't tall
+    probe.assert_image_size(200, 100)
 
     # Make the parent a flex column
     widget.parent.style.direction = COLUMN
@@ -87,17 +102,20 @@ async def test_explicit_width(widget, probe, container_probe):
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(container_probe.height, abs=2)
     assert probe.preserve_aspect_ratio
+    # Container has fixed width; aspect ratio is preserved, image is implicit height
+    probe.assert_image_size(200, 100)
 
 
 async def test_explicit_height(widget, probe, container_probe):
     """If the image height is explicit, the image view will resize preserving aspect ratio."""
-    # Explicitly set height
+    # Explicitly set height; width follows aspect raio
     widget.style.height = 150
 
     await probe.redraw("Image has explicit height")
     assert probe.width == pytest.approx(300, abs=2)
     assert probe.height == pytest.approx(150, abs=2)
     assert probe.preserve_aspect_ratio
+    probe.assert_image_size(300, 150)
 
     # Clear the image; it's now an explicit sized empty image.
     widget.image = None
@@ -116,6 +134,8 @@ async def test_explicit_height(widget, probe, container_probe):
     assert probe.width == pytest.approx(container_probe.width, abs=2)
     assert probe.height == pytest.approx(150, abs=2)
     assert probe.preserve_aspect_ratio
+    # Container has fixed height; aspect ratio is preserved, so image isn't wide
+    probe.assert_image_size(300, 150)
 
     # Make the parent a flex column
     widget.parent.style.direction = COLUMN
@@ -124,6 +144,8 @@ async def test_explicit_height(widget, probe, container_probe):
     assert probe.width == pytest.approx(container_probe.width, abs=2)
     assert probe.height == pytest.approx(150, abs=2)
     assert probe.preserve_aspect_ratio
+    # Container has fixed height; aspect ratio is preserved, image is implicit height
+    probe.assert_image_size(300, 150)
 
 
 async def test_explicit_size(widget, probe):
@@ -136,6 +158,8 @@ async def test_explicit_size(widget, probe):
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(300, abs=2)
     assert not probe.preserve_aspect_ratio
+    # Image is the size specified.
+    probe.assert_image_size(200, 300)
 
     # Clear the image; it's now an explicit sized empty image.
     widget.image = None
@@ -154,6 +178,8 @@ async def test_explicit_size(widget, probe):
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(300, abs=2)
     assert not probe.preserve_aspect_ratio
+    # Image is the size specified.
+    probe.assert_image_size(200, 300)
 
     # Make the parent a flex column
     widget.parent.style.direction = COLUMN
@@ -162,3 +188,5 @@ async def test_explicit_size(widget, probe):
     assert probe.width == pytest.approx(200, abs=2)
     assert probe.height == pytest.approx(300, abs=2)
     assert not probe.preserve_aspect_ratio
+    # Image is the size specified.
+    probe.assert_image_size(200, 300)

winforms/tests_backend/widgets/imageview.py

@@ -9,3 +9,8 @@ class ImageViewProbe(SimpleProbe):
     @property
     def preserve_aspect_ratio(self):
         return self.native.SizeMode == WinForms.PictureBoxSizeMode.Zoom
+
+    def assert_image_size(self, width, height):
+        # Winforms internally scales the image to the container,
+        # so there's no image size check required.
+        pass