fix layout of image when either width or height is bounded, but not the other

AUTHORS

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

CHANGELOG.md

@@ -42,6 +42,7 @@ You can find its changes [documented below](#060---2020-06-01).
 
 ### Fixed
 
+- `widget::Imge` now computes the layout correctly when unbound in one direction. ([#1189] by [@JAicewizard])
 - macOS: Timers not firing during modal loop. ([#1028] by [@xStrom])
 - GTK: Directory selection now properly ignores file filters. ([#957] by [@xStrom])
 - GTK: Don't crash when receiving an external command while a file dialog is visible. ([#1043] by [@jneem])
@@ -278,7 +279,7 @@ Last release without a changelog :(
 [@sysint64]: https://github.com/sysint64
 [@justinmoon]: https://github.com/justinmoon
 [@rjwittams]: https://github.com/rjwittams
-
+[@JAicewizard]: https://github.com/JAicewizard
 [#599]: https://github.com/linebender/druid/pull/599
 [#611]: https://github.com/linebender/druid/pull/611
 [#695]: https://github.com/linebender/druid/pull/695
@@ -412,7 +413,7 @@ Last release without a changelog :(
 [#1171]: https://github.com/linebender/druid/pull/1171
 [#1172]: https://github.com/linebender/druid/pull/1172
 [#1173]: https://github.com/linebender/druid/pull/1173
-
+[#1186]: https://github.com/linebender/druid/pull/1186
 [Unreleased]: https://github.com/linebender/druid/compare/v0.6.0...master
 [0.6.0]: https://github.com/linebender/druid/compare/v0.5.0...v0.6.0
 [0.5.0]: https://github.com/linebender/druid/compare/v0.4.0...v0.5.0

druid/src/widget/image.rs

@@ -145,8 +145,19 @@ 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.
+        if !bc.is_height_bounded() && bc.is_width_bounded() {
+            let mut size = bc.max();
+            let ratio = size.width / self.image_data.x_pixels as f64;
+            size.height = ratio * self.image_data.y_pixels as f64;
+            size
+        } else if !bc.is_width_bounded() && bc.is_height_bounded() {
+            let mut size = bc.max();
+            let ratio = size.height / self.image_data.y_pixels as f64;
+            size.width = ratio * self.image_data.x_pixels as f64;
+            size
         } else {
             bc.constrain(self.image_data.get_size())
         }
@@ -438,4 +449,104 @@ mod tests {
             },
         );
     }
+
+    #[test]
+    fn width_bound_paint() {
+        use crate::{tests::harness::Harness, widget::Scroll, WidgetId};
+        let _id_1 = WidgetId::next();
+        let image_data = ImageData {
+            pixels: vec![255, 255, 255, 0, 0, 0, 0, 0, 0, 255, 255, 255],
+            x_pixels: 2,
+            y_pixels: 2,
+            format: ImageFormat::Rgb,
+        };
+
+        let image_widget =
+            Image::new(image_data).interpolation_mode(InterpolationMode::NearestNeighbor);
+
+        Harness::create_with_render(
+            true,
+            Scroll::new(image_widget).vertical(),
+            Size::new(400., 400.),
+            |harness| {
+                harness.send_initial_events();
+                harness.just_layout();
+                harness.paint();
+            },
+            |target| {
+                // the width should be calculated to be 400.
+                let width = 400;
+                let raw_pixels = target.into_raw();
+                assert_eq!(raw_pixels.len(), 400 * width * 4);
+
+                // Being a height bound widget every row will have no padding at the start and end._id_1
+
+                // The image starts at (0,0), so 200 white and then 200 black.
+                let expecting: Vec<u8> = [
+                    vec![255, 255, 255, 255].repeat(200),
+                    vec![0, 0, 0, 255].repeat(200),
+                ]
+                .concat();
+                assert_eq!(raw_pixels[199 * width * 4..200 * width * 4], expecting[..]);
+
+                // The final row of 400 pixels is 200 white and then 200 black.
+                let expecting: Vec<u8> = [
+                    vec![0, 0, 0, 255].repeat(200),
+                    vec![255, 255, 255, 255].repeat(200),
+                ]
+                .concat();
+                assert_eq!(raw_pixels[200 * width * 4..201 * width * 4], expecting[..]);
+            },
+        );
+    }
+
+    #[test]
+    fn height_bound_paint() {
+        use crate::{tests::harness::Harness, widget::Scroll, WidgetId};
+        let _id_1 = WidgetId::next();
+        let image_data = ImageData {
+            pixels: vec![255, 255, 255, 0, 0, 0, 0, 0, 0, 255, 255, 255],
+            x_pixels: 2,
+            y_pixels: 2,
+            format: ImageFormat::Rgb,
+        };
+
+        let image_widget =
+            Image::new(image_data).interpolation_mode(InterpolationMode::NearestNeighbor);
+
+        Harness::create_with_render(
+            true,
+            Scroll::new(image_widget).horizontal(),
+            Size::new(400., 400.),
+            |harness| {
+                harness.send_initial_events();
+                harness.just_layout();
+                harness.paint();
+            },
+            |target| {
+                // the width should be calculated to be 400.
+                let width = 400;
+                let raw_pixels = target.into_raw();
+                assert_eq!(raw_pixels.len(), 400 * width * 4);
+
+                // Being a height bound widget every row will have no padding at the start and end._id_1
+
+                // The image starts at (0,0), so 200 black and then 200 white.
+                let expecting: Vec<u8> = [
+                    vec![255, 255, 255, 255].repeat(200),
+                    vec![0, 0, 0, 255].repeat(200),
+                ]
+                .concat();
+                assert_eq!(raw_pixels[199 * width * 4..200 * width * 4], expecting[..]);
+
+                // The final row of 400 pixels is 200 white and then 200 black.
+                let expecting: Vec<u8> = [
+                    vec![0, 0, 0, 255].repeat(200),
+                    vec![255, 255, 255, 255].repeat(200),
+                ]
+                .concat();
+                assert_eq!(raw_pixels[200 * width * 4..201 * width * 4], expecting[..]);
+            },
+        );
+    }
 }