slidingView: Allocate LpImage more correctly

Allocate the ScrolledWindow instead of the LpImage
to include non-overlayed scrollbars.

General cleanup how we measure things.

Part-of: <https://gitlab.gnome.org/Incubator/loupe/-/merge_requests/150>

src/widgets/image_page.rs

@@ -48,6 +48,8 @@ mod imp {
         #[template_child]
         pub(super) image_stack_page: TemplateChild<gtk::Widget>,
         #[template_child]
+        pub(super) scrolled_window: TemplateChild<gtk::ScrolledWindow>,
+        #[template_child]
         pub(super) image: TemplateChild<LpImage>,
         #[template_child]
         pub(super) popover: TemplateChild<gtk::PopoverMenu>,
@@ -165,6 +167,10 @@ impl LpImagePage {
         self.image().path().unwrap()
     }
 
+    pub fn scrolled_window(&self) -> gtk::ScrolledWindow {
+        self.imp().scrolled_window.clone()
+    }
+
     pub fn image(&self) -> LpImage {
         self.imp().image.get()
     }

src/widgets/image_view.rs

@@ -194,14 +194,7 @@ mod imp {
     }
 
     impl WidgetImpl for LpImageView {
-        /// The main target of this manual implementation is to provide a good
+        /// This manual implementation makes sure left an right overlay both fit into the window
-        /// natural width that allows to have a neat size for newly opened `LpWindow`s.
-        /// The actual calculation of the image natural width happens in
-        /// the measure function of `LpImage`.
-        ///
-        /// This manual implementation is necessary since AdwCarousel gives the
-        /// largest natural width of all of it's children. But we actually want the
-        /// one of the opened (current) image.
         fn measure(&self, orientation: gtk::Orientation, for_size: i32) -> (i32, i32, i32, i32) {
             // Measure child of AdwBin
             let (child_min, child_natural, _, _) = self.bin_child.measure(orientation, for_size);
@@ -212,19 +205,10 @@ mod imp {
 
             // take as minimum whatever is larger
             let min = i32::max(child_min, overlay1_min + overlay2_min);
+            // take as natural whatever is larger
+            let natural = i32::max(child_natural, min);
 
-            if let Some(page) = self.obj().current_page() {
+            (min, natural, -1, -1)
-                // measure `LpImage`
-                let (_, image_natural, _, _) = page.image().measure(orientation, for_size);
-
-                // Ensure that minimum size is not smaller than the one of the child.
-                // Also ensure that the natural width is not smaller than the minimal size.
-                // Both things are required by GTK.
-                (min, i32::max(min, image_natural), -1, -1)
-            } else {
-                // also include controls overlays when mostly passing through child measurements
-                (min, i32::max(child_natural, min), -1, -1)
-            }
         }
 
         /// this is necessary because we do layout manually

src/widgets/sliding_view.rs

@@ -165,14 +165,17 @@ mod imp {
                 if page_position == (scroll_position + position_shift).floor()
                     || page_position == (scroll_position + position_shift).ceil()
                 {
-                    page.set_visible(true);
+                    page.set_child_visible(true);
+                    let transform = gsk::Transform::new().translate(&graphene::Point::new(x, 0.));
+                    page.allocate(width, height, 0, Some(transform));
                 } else {
-                    page.set_visible(false);
+                    page.set_child_visible(false);
                 }
 
-                let transform = gsk::Transform::new().translate(&graphene::Point::new(x, 0.));
+                if !page.scrolled_window().is_mapped() {
-                page.allocate(width, height, 0, Some(transform));
+                    // SVG needs to know a widget size before rendering something in LpImage
-                page.image().allocate(width, height, 0, None);
+                    page.scrolled_window().allocate(width, height, 0, None);
+                }
             }
         }