[gnome-shell] js/ui: Choose some actors to cache on the GPU

[Jonas Ådahl <jadahl src gnome org>]

commit f77b3da74fccfd8baa160e26a0ebf51c2baa5f83
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Fri Apr 6 18:26:58 2018 +0800

    js/ui: Choose some actors to cache on the GPU
    
    Flag some actors that are good candidates for caching in texture memory
    (what Clutter calls "offscreen redirect"), thereby mostly eliminating
    their repaint overhead.
    
    This isn't exactly groundbreaking, it's how you're meant to use
    OpenGL in the first place. But the difficulty is in the design of
    Clutter which has some peculiarities making universal caching
    inefficient at the moment:
    
     * Repainting an offscreen actor is measurably slower than repainting
       the same actor if it was uncached. But only by less than 100%,
       so if an actor can avoid changing every frame then caching is usually
       more efficient over that timeframe.
    
     * The cached painting from a container typically includes its children,
       so you can't cache containers whose children are usually animating at
       full frame rate. That results in a performance loss.
         This could be remedied in future by Clutter explicitly separating a
       container's background painting from its child painting and always
       caching the background (as StWidget tries to in some cases already).
    
    So this commit selects just a few areas where caching has been verified
    to be beneficial, and many use cases now see their CPU usage halved:
    
    One small window active...... 10% -> 7% (-30%)
    ...under a panel menu........ 23% -> 9% (-61%)
    One maximized window active.. 12% -> 9% (-25%)
    ...under a panel menu........ 23% -> 11% (-52%)
    ...under a shell dialog...... 22% -> 12% (-45%)
    ...in activities overview.... 32% -> 17% (-47%)
    (on an i7-7700)
    
    Also a couple of bugs are fixed by this:
    
    https://bugzilla.gnome.org/show_bug.cgi?id=792634
    https://bugzilla.gnome.org/show_bug.cgi?id=792633

 js/ui/boxpointer.js | 1 +
 js/ui/dash.js       | 1 +
 js/ui/dialog.js     | 1 +
 js/ui/panel.js      | 1 +
 4 files changed, 4 insertions(+)
---
diff --git a/js/ui/boxpointer.js b/js/ui/boxpointer.js
index 47f718a84..d51877d18 100644
--- a/js/ui/boxpointer.js
+++ b/js/ui/boxpointer.js
@@ -44,6 +44,7 @@ var BoxPointer = new Lang.Class({
                                   y_fill: true });
         this._container = new Shell.GenericContainer();
         this.actor.set_child(this._container);
+        this.actor.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
         this._container.connect('get-preferred-width', this._getPreferredWidth.bind(this));
         this._container.connect('get-preferred-height', this._getPreferredHeight.bind(this));
         this._container.connect('allocate', this._allocate.bind(this));
diff --git a/js/ui/dash.js b/js/ui/dash.js
index 5ee2476e3..9b8bfdd13 100644
--- a/js/ui/dash.js
+++ b/js/ui/dash.js
@@ -402,6 +402,7 @@ var Dash = new Lang.Class({
                                        clip_to_allocation: true });
         this._box._delegate = this;
         this._container.add_actor(this._box);
+        this._container.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
 
         this._showAppsIcon = new ShowAppsIcon();
         this._showAppsIcon.childScale = 1;
diff --git a/js/ui/dialog.js b/js/ui/dialog.js
index cfa192db7..0dd33706b 100644
--- a/js/ui/dialog.js
+++ b/js/ui/dialog.js
@@ -40,6 +40,7 @@ var Dialog = new Lang.Class({
         // mode accordingly so wrapped labels are handled correctly during
         // size requests.
         this._dialog.request_mode = Clutter.RequestMode.HEIGHT_FOR_WIDTH;
+        this._dialog.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
 
         this.contentLayout = new St.BoxLayout({ vertical: true,
                                                 style_class: "modal-dialog-content-box" });
diff --git a/js/ui/panel.js b/js/ui/panel.js
index 05241abdc..4fd599c47 100644
--- a/js/ui/panel.js
+++ b/js/ui/panel.js
@@ -776,6 +776,7 @@ var Panel = new Lang.Class({
         this.actor = new Shell.GenericContainer({ name: 'panel',
                                                   reactive: true });
         this.actor._delegate = this;
+        this.actor.set_offscreen_redirect(Clutter.OffscreenRedirect.ALWAYS);
 
         this._sessionStyle = null;