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

diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index c4cc047dcaf66ac6b86771343c2c79a7dfe26ab2..411a1d6ca38031202a8c5521c163a29db31422cf 100644 (file)
--- 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();