[gnome-shell] dnd: Make the draggable much faster

[Jasper St. Pierre <jstpierre src gnome org>]

commit 317b9a9c87808b19dd855426fadbd7314bdc837b
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Tue Jul 2 02:04:08 2013 -0400

    dnd: Make the draggable much faster
    
    It turns out that picking a 3200x1200 scene on notebook chipsets
    every time the mouse is moved isn't exactly the fastest thing. Defer
    picking to an idle to ensure that it won't get in the way of keeping
    up with mouse events.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=703443

 js/ui/dnd.js |  107 ++++++++++++++++++++++++++++++++--------------------------
 1 files changed, 59 insertions(+), 48 deletions(-)
---
diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index c4cc047..411a1d6 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -1,6 +1,7 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
 const Clutter = imports.gi.Clutter;
+const GLib = imports.gi.GLib;
 const Gtk = imports.gi.Gtk;
 const St = imports.gi.St;
 const Lang = imports.lang;
@@ -358,60 +359,65 @@ const _Draggable = new Lang.Class({
         return true;
     },
 
-    _updateDragPosition : function (event) {
-        let [stageX, stageY] = event.get_coords();
-        this._dragX = stageX;
-        this._dragY = stageY;
-
-        // If we are dragging, update the position
-        if (this._dragActor) {
-            this._dragActor.set_position(stageX + this._dragOffsetX,
-                                         stageY + this._dragOffsetY);
-
-            let target = this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
-                                                                      stageX, stageY);
-
-            // We call observers only once per motion with the innermost
-            // target actor. If necessary, the observer can walk the
-            // parent itself.
-            let dragEvent = {
-                x: stageX,
-                y: stageY,
-                dragActor: this._dragActor,
-                source: this.actor._delegate,
-                targetActor: target
-            };
-            for (let i = 0; i < dragMonitors.length; i++) {
-                let motionFunc = dragMonitors[i].dragMotion;
-                if (motionFunc) {
-                    let result = motionFunc(dragEvent);
-                    if (result != DragMotionResult.CONTINUE) {
-                        global.set_cursor(DRAG_CURSOR_MAP[result]);
-                        return true;
-                    }
+    _updateDragHover : function () {
+        let target = this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
+                                                                  this._dragX, this._dragY);
+        let dragEvent = {
+            x: this._dragX,
+            y: this._dragY,
+            dragActor: this._dragActor,
+            source: this.actor._delegate,
+            targetActor: target
+        };
+        for (let i = 0; i < dragMonitors.length; i++) {
+            let motionFunc = dragMonitors[i].dragMotion;
+            if (motionFunc) {
+                let result = motionFunc(dragEvent);
+                if (result != DragMotionResult.CONTINUE) {
+                    global.set_cursor(DRAG_CURSOR_MAP[result]);
+                    return false;
                 }
             }
-            while (target) {
-                if (target._delegate && target._delegate.handleDragOver) {
-                    let [r, targX, targY] = target.transform_stage_point(stageX, stageY);
-                    // We currently loop through all parents on drag-over even if one of the children has 
handled it.
-                    // We can check the return value of the function and break the loop if it's true if we 
don't want
-                    // to continue checking the parents.
-                    let result = target._delegate.handleDragOver(this.actor._delegate,
-                                                                 this._dragActor,
-                                                                 targX,
-                                                                 targY,
-                                                                 event.get_time());
-                    if (result != DragMotionResult.CONTINUE) {
-                        global.set_cursor(DRAG_CURSOR_MAP[result]);
-                        return true;
-                    }
+        }
+
+        while (target) {
+            if (target._delegate && target._delegate.handleDragOver) {
+                let [r, targX, targY] = target.transform_stage_point(this._dragX, this._dragY);
+                // We currently loop through all parents on drag-over even if one of the children has 
handled it.
+                // We can check the return value of the function and break the loop if it's true if we don't 
want
+                // to continue checking the parents.
+                let result = target._delegate.handleDragOver(this.actor._delegate,
+                                                             this._dragActor,
+                                                             targX,
+                                                             targY,
+                                                             0);
+                if (result != DragMotionResult.CONTINUE) {
+                    global.set_cursor(DRAG_CURSOR_MAP[result]);
+                    return false;
                 }
-                target = target.get_parent();
             }
-            global.set_cursor(Shell.Cursor.DND_IN_DRAG);
+            target = target.get_parent();
         }
+        global.set_cursor(Shell.Cursor.DND_IN_DRAG);
+        return false;
+    },
+
+    _queueUpdateDragHover: function() {
+        if (this._updateHoverId)
+            GLib.source_remove(this._updateHoverId);
+
+        this._updateHoverId = GLib.idle_add(GLib.PRIORITY_DEFAULT,
+                                            Lang.bind(this, this._updateDragHover));
+    },
 
+    _updateDragPosition : function (event) {
+        let [stageX, stageY] = event.get_coords();
+        this._dragX = stageX;
+        this._dragY = stageY;
+        this._dragActor.set_position(stageX + this._dragOffsetX,
+                                     stageY + this._dragOffsetY);
+
+        this._queueUpdateDragHover();
         return true;
     },
 
@@ -511,6 +517,11 @@ const _Draggable = new Lang.Class({
     },
 
     _cancelDrag: function(eventTime) {
+        if (this._updateHoverId) {
+            GLib.source_remove(this._updateHoverId);
+            this._updateHoverId = 0;
+        }
+
         this.emit('drag-cancelled', eventTime);
         this._dragInProgress = false;
         let [snapBackX, snapBackY, snapBackScale] = this._getRestoreLocation();