[Qt] Support ImageView

changes/3914.feature.3.md

@@ -0,0 +1 @@
+The ImageView widget is now supported in the Qt backend.

docs/en/reference/data/apis_by_platform.yaml

@@ -81,7 +81,6 @@ General widgets:
     unsupported:
       - web
       - textual
-      - qt
 
   Label:
     description: A text label for annotating forms or interfaces.

qt/src/toga_qt/factory.py

@@ -14,6 +14,7 @@
     from .widgets.activityindicator import ActivityIndicator
     from .widgets.box import Box
     from .widgets.button import Button
+    from .widgets.imageview import ImageView
     from .widgets.label import Label
     from .widgets.textinput import TextInput
     from .window import MainWindow, Window
@@ -44,6 +45,7 @@
     "Box",
     "Label",
     "TextInput",
+    "ImageView",
     "dialogs",
 ]
 

qt/src/toga_qt/widgets/box.py

@@ -11,7 +11,7 @@ def create(self):
         self.native.setAutoFillBackground(True)
         # Background is not autofilled by default; but since we're
         # enabling it here, let the default color be transparent
-        # so it autofills nothing.
+        # so it autofills nothing by default.
         self._default_background_color = TRANSPARENT
 
     def rehint(self):

qt/src/toga_qt/widgets/imageview.py

@@ -0,0 +1,46 @@
+from PySide6.QtCore import Qt
+from PySide6.QtGui import QPixmap
+from PySide6.QtWidgets import QLabel
+from travertino.constants import TRANSPARENT
+
+from toga.widgets.imageview import rehint_imageview
+
+from .base import Widget
+
+
+class ImageView(Widget):
+    def create(self):
+        self.native = QLabel()
+        self.native.setAlignment(Qt.AlignCenter)
+        self._aspect_ratio = None
+        self.native.setAutoFillBackground(True)
+        # Background is not autofilled by default; but since we're
+        # enabling it here, let the default color be transparent
+        # so it autofills nothing by default.
+        self._default_background_color = TRANSPARENT
+
+    def set_image(self, image):
+        if image:
+            self.set_scaled_pixbuf(image._impl.native)
+        else:
+            self.native.setPixmap(QPixmap())
+
+    def set_scaled_pixbuf(self, image):
+        scaled = QPixmap.fromImage(image).scaled(
+            self.native.size(),
+            Qt.KeepAspectRatio if self._aspect_ratio else Qt.IgnoreAspectRatio,
+            Qt.SmoothTransformation,
+        )
+        self.native.setPixmap(scaled)
+
+    def set_bounds(self, *args):
+        super().set_bounds(*args)
+        if self.interface.image:
+            self.set_scaled_pixbuf(self.interface.image._impl.native)
+
+    def rehint(self):
+        width, height, self._aspect_ratio = rehint_imageview(
+            image=self.interface.image, style=self.interface.style
+        )
+        self.interface.intrinsic.width = width
+        self.interface.intrinsic.height = height

qt/tests_backend/widgets/box.py

@@ -6,3 +6,7 @@
 class BoxProbe(SimpleProbe):
     native_class = QWidget
     invalid_size_while_hidden = False
+
+    def __init__(self, widget):
+        super().__init__(widget)
+        assert self.native.autoFillBackground()

qt/tests_backend/widgets/imageview.py

@@ -0,0 +1,19 @@
+from PySide6.QtWidgets import QLabel
+
+from .base import SimpleProbe
+
+
+class ImageViewProbe(SimpleProbe):
+    native_class = QLabel
+
+    def __init__(self, widget):
+        super().__init__(widget)
+        assert self.native.autoFillBackground()
+
+    @property
+    def preserve_aspect_ratio(self):
+        return self.impl._aspect_ratio is not None
+
+    def assert_image_size(self, width, height):
+        pixmap = self.native.pixmap()
+        assert (pixmap.width(), pixmap.height()) == (width, height)

qt/tests_backend/widgets/label.py

@@ -7,6 +7,10 @@
 class LabelProbe(SimpleProbe):
     native_class = QLabel
 
+    def __init__(self, widget):
+        super().__init__(widget)
+        assert self.native.autoFillBackground()
+
     @property
     def text(self):
         return self.native.text()