image: Add double click for zoom/fullscreen

Zooms on touchscreens and fullscreens otherwise.
Using the fullscreen behavior for now, since that's what
a lot of other apps do.

data/gtk/image_page.ui

@@ -63,7 +63,7 @@
             <property name="child">
               <object class="LpImage" id="image">
                 <child>
-                  <object class="GtkGestureClick" id="click_gesture">
+                  <object class="GtkGestureClick" id="right_click_gesture">
                     <property name="button">3</property>
                   </object>
                 </child>

src/widgets/image.rs

@@ -30,13 +30,22 @@ use once_cell::unsync::OnceCell;
 use std::cell::{Cell, RefCell};
 use std::path::{Path, PathBuf};
 
+/// Milliseconds
 const ZOOM_ANIMATION_DURATION: u32 = 200;
+/// Milliseconds
 const ROTATION_ANIMATION_DURATION: u32 = 200;
 
+/// Relative to current zoom level
 const ZOOM_FACTOR_BUTTON: f64 = 1.5;
+/// Relative to current zoom level
 const ZOOM_FACTOR_WHEEL: f64 = 1.3;
-const ZOOM_FACTOR_WHEEL_HI_RES: f64 = 0.1;
+/// Relative to current zoom level
+const ZOOM_FACTOR_WHEEL_HI_RES: f64 = 0.001;
 
+/// Relative to best-fit level
+const ZOOM_FACTOR_DOUBLE_TAP: f64 = 2.5;
+
+/// Max zoom level 2000%
 const MAX_ZOOM_LEVEL: f64 = 20.0;
 
 mod imp {
@@ -304,6 +313,33 @@ mod imp {
         fn connect_gestures(&self) {
             let obj = self.instance();
 
+            // Double click for fullscreen (mouse/touchpad) or zoom (touch screen)
+            let left_click_gesture = gtk::GestureClick::builder().button(1).build();
+            obj.add_controller(&left_click_gesture);
+            left_click_gesture.connect_pressed(
+                glib::clone!(@weak obj => move |gesture, n_press, x, y| {
+                    // only handle double clicks
+                    if n_press != 2 {
+                        return;
+                    }
+
+                    if gesture.device().map(|x| x.source()) == Some(gdk::InputSource::Touchscreen) {
+                        // zoom
+                        obj.imp().pointer_position.set(Some((x, y)));
+                        if obj.is_best_fit() {
+                            // zoom in
+                            obj.zoom_to(ZOOM_FACTOR_DOUBLE_TAP * obj.zoom_level_best_fit());
+                        } else {
+                            // zoom back out
+                            obj.zoom_best_fit();
+                        }
+                    } else {
+                        // fullscreen
+                        obj.activate_action("win.toggle-fullscreen", None).unwrap();
+                    }
+                }),
+            );
+
             // Drag for moving image around
             let drag_gesture = gtk::GestureDrag::new();
             obj.add_controller(&drag_gesture);

src/widgets/image_page.rs

@@ -49,7 +49,7 @@ mod imp {
         #[template_child]
         pub(super) popover: TemplateChild<gtk::PopoverMenu>,
         #[template_child]
-        pub(super) click_gesture: TemplateChild<gtk::GestureClick>,
+        pub(super) right_click_gesture: TemplateChild<gtk::GestureClick>,
         #[template_child]
         pub(super) press_gesture: TemplateChild<gtk::GestureLongPress>,
 
@@ -100,7 +100,7 @@ mod imp {
 
             self.parent_constructed();
 
-            self.click_gesture
+            self.right_click_gesture
                 .connect_pressed(clone!(@weak obj => move |gesture, _, x, y| {
                     obj.show_popover_at(x, y);
                     gesture.set_state(gtk::EventSequenceState::Claimed);