h-gtk: Animate the adjustment of scrolled windows.

Many thanks to Julian Spaber for documenting this.

hammond-gtk/src/utils.rs

@@ -1,5 +1,6 @@
 #![cfg_attr(feature = "cargo-clippy", allow(type_complexity))]
 
+use gdk::FrameClockExt;
 use gdk_pixbuf::Pixbuf;
 use glib;
 use gtk;
@@ -101,6 +102,40 @@ where
     });
 }
 
+// Kudos to Julian Sparber
+// https://blogs.gnome.org/jsparber/2018/04/29/animate-a-scrolledwindow/
+pub fn smooth_scroll_to(view: gtk::ScrolledWindow, target: gtk::Adjustment) {
+    if let Some(adj) = view.get_vadjustment() {
+        if let Some(clock) = view.get_frame_clock() {
+            let duration = 200;
+            let start = adj.get_value();
+            let end = target.get_value();
+            let start_time = clock.get_frame_time();
+            let end_time = start_time + 1000 * duration;
+
+            view.add_tick_callback(move |_, clock| {
+                let now = clock.get_frame_time();
+                if now < end_time && adj.get_value() != end {
+                    let mut t = (now - start_time) as f64 / (end_time - start_time) as f64;
+                    t = ease_out_cubic(t);
+                    adj.set_value(start + t * (end - start));
+                    return glib::Continue(true);
+                } else {
+                    adj.set_value(end);
+                    return glib::Continue(false);
+                }
+            });
+        }
+    }
+}
+
+// From clutter-easing.c, based on Robert Penner's
+// infamous easing equations, MIT license.
+fn ease_out_cubic(t: f64) -> f64 {
+    let p = t - 1f64;
+    return p * p * p + 1f64;
+}
+
 lazy_static! {
     static ref IGNORESHOWS: Arc<Mutex<HashSet<i32>>> = Arc::new(Mutex::new(HashSet::new()));
 }

hammond-gtk/src/widgets/home_view.rs

@@ -1,5 +1,6 @@
 use chrono::prelude::*;
 use failure::Error;
+
 use gtk;
 use gtk::prelude::*;
 
@@ -8,8 +9,7 @@ use hammond_data::EpisodeWidgetQuery;
 use send_cell::SendCell;
 
 use app::Action;
-use utils::lazy_load_full;
-use utils::{get_ignored_shows, set_image_from_path};
+use utils::{self, lazy_load_full};
 use widgets::EpisodeWidget;
 
 use std::rc::Rc;
@@ -90,7 +90,7 @@ impl HomeView {
         use self::ListSplit::*;
 
         let view = Rc::new(HomeView::default());
-        let ignore = get_ignored_shows()?;
+        let ignore = utils::get_ignored_shows()?;
         let episodes = dbqueries::get_episodes_widgets_filter_limit(&ignore, 100)?;
         let now_utc = Utc::now();
 
@@ -132,7 +132,7 @@ impl HomeView {
             // Copy the vertical scrollbar adjustment from the old view into the new one.
             sendcell
                 .try_get()
-                .map(|x| self.scrolled_window.set_vadjustment(&x));
+                .map(|x| utils::smooth_scroll_to(self.scrolled_window.clone(), x.clone()));
         }
 
         Ok(())
@@ -231,6 +231,6 @@ impl EpisodesViewWidget {
 
     #[inline]
     fn set_cover(&self, podcast_id: i32) -> Result<(), Error> {
-        set_image_from_path(&self.image, podcast_id, 64)
+        utils::set_image_from_path(&self.image, podcast_id, 64)
     }
 }

hammond-gtk/src/widgets/show.rs

@@ -165,7 +165,7 @@ impl ShowWidget {
             // Copy the vertical scrollbar adjustment from the old view into the new one.
             sendcell
                 .try_get()
-                .map(|x| self.scrolled_window.set_vadjustment(&x));
+                .map(|x| utils::smooth_scroll_to(self.scrolled_window.clone(), x.clone()));
         }
 
         Ok(())