Fix layout of image when either width or height is bounded, but not the other (#1189)

Author: JAicewizard

AUTHORS

@@ -13,3 +13,4 @@ Leopold Luley
 Andrey Kabylin
 Garrett Risley
 Robert Wittams
+Jaap Aarts

CHANGELOG.md

@@ -97,6 +97,7 @@ You can find its changes [documented below](#060---2020-06-01).
 - Multi-click on Windows, partial fix for #859 ([#1157] by [@raphlinus])
 - Windows: fix crash on resize from incompatible resources ([#1191 by [@raphlinus]])
 - GTK: Related dependencies are now optional, facilitating a pure X11 build. ([#1241] by [@finnerale])
+- `widget::Image` now computes the layout correctly when unbound in one direction. ([#1189] by [@JAicewizard])
 
 ### Visual
 
@@ -322,6 +323,7 @@ Last release without a changelog :(
 [@rhzk]: https://github.com/rhzk
 [@koutoftimer]: https://github.com/koutoftimer
 [@tay64]: https://github.com/tay64
+[@JAicewizard]: https://github.com/JAicewizard
 
 [#599]: https://github.com/linebender/druid/pull/599
 [#611]: https://github.com/linebender/druid/pull/611
@@ -465,6 +467,7 @@ Last release without a changelog :(
 [#1185]: https://github.com/linebender/druid/pull/1185
 [#1191]: https://github.com/linebender/druid/pull/1191
 [#1092]: https://github.com/linebender/druid/pull/1092
+[#1189]: https://github.com/linebender/druid/pull/1189
 [#1195]: https://github.com/linebender/druid/pull/1195
 [#1204]: https://github.com/linebender/druid/pull/1204
 [#1205]: https://github.com/linebender/druid/pull/1205

druid/src/widget/image.rs

@@ -145,8 +145,17 @@ impl<T: Data> Widget<T> for Image {
     ) -> Size {
         bc.debug_check("Image");
 
-        if bc.is_width_bounded() {
-            bc.max()
+        // If either the width or height is constrained calculate a value so that the image fits
+        // in the size exactly. If it is unconstrained by both width and height take the size of
+        // the image.
+        let max = bc.max();
+        let image_size = self.image_data.size();
+        if bc.is_width_bounded() && !bc.is_height_bounded() {
+            let ratio = max.width / image_size.width;
+            Size::new(max.width, ratio * image_size.height)
+        } else if bc.is_height_bounded() && !bc.is_width_bounded() {
+            let ratio = max.height / image_size.height;
+            Size::new(ratio * image_size.width, max.height)
         } else {
             bc.constrain(self.image_data.size())
         }
@@ -317,4 +326,60 @@ mod tests {
             },
         );
     }
+
+    #[test]
+    fn width_bound_layout() {
+        use crate::{
+            tests::harness::Harness,
+            widget::{Container, Scroll},
+            WidgetExt, WidgetId,
+        };
+        use float_cmp::approx_eq;
+
+        let id_1 = WidgetId::next();
+        let image_data = ImageBuf::from_raw(
+            vec![255, 255, 255, 0, 0, 0, 0, 0, 0, 255, 255, 255],
+            ImageFormat::Rgb,
+            2,
+            2,
+        );
+
+        let image_widget =
+            Scroll::new(Container::new(Image::new(image_data)).with_id(id_1)).vertical();
+
+        Harness::create_simple(true, image_widget, |harness| {
+            harness.send_initial_events();
+            harness.just_layout();
+            let state = harness.get_state(id_1);
+            assert!(approx_eq!(f64, state.layout_rect().x1, 400.0));
+        })
+    }
+
+    #[test]
+    fn height_bound_layout() {
+        use crate::{
+            tests::harness::Harness,
+            widget::{Container, Scroll},
+            WidgetExt, WidgetId,
+        };
+        use float_cmp::approx_eq;
+
+        let id_1 = WidgetId::next();
+        let image_data = ImageBuf::from_raw(
+            vec![255, 255, 255, 0, 0, 0, 0, 0, 0, 255, 255, 255],
+            ImageFormat::Rgb,
+            2,
+            2,
+        );
+
+        let image_widget =
+            Scroll::new(Container::new(Image::new(image_data)).with_id(id_1)).horizontal();
+
+        Harness::create_simple(true, image_widget, |harness| {
+            harness.send_initial_events();
+            harness.just_layout();
+            let state = harness.get_state(id_1);
+            assert!(approx_eq!(f64, state.layout_rect().x1, 400.0));
+        })
+    }
 }