gnome-shell/js/ui/dnd.js

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// -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
/* exported addDragMonitor, removeDragMonitor, makeDraggable */
const { Clutter, GLib, Meta, Shell, St } = imports.gi;
const Signals = imports.signals;
const Main = imports.ui.main;
const Params = imports.misc.params;
// Time to scale down to maxDragActorSize
var SCALE_ANIMATION_TIME = 250;
// Time to animate to original position on cancel
var SNAP_BACK_ANIMATION_TIME = 250;
// Time to animate to original position on success
var REVERT_ANIMATION_TIME = 750;
var DragMotionResult = {
NO_DROP: 0,
COPY_DROP: 1,
MOVE_DROP: 2,
CONTINUE: 3,
};
var DragState = {
INIT: 0,
DRAGGING: 1,
CANCELLED: 2,
};
var DRAG_CURSOR_MAP = {
0: Meta.Cursor.DND_UNSUPPORTED_TARGET,
1: Meta.Cursor.DND_COPY,
2: Meta.Cursor.DND_MOVE,
};
var DragDropResult = {
FAILURE: 0,
SUCCESS: 1,
CONTINUE: 2,
};
var dragMonitors = [];
let eventHandlerActor = null;
let currentDraggable = null;
function _getEventHandlerActor() {
if (!eventHandlerActor) {
eventHandlerActor = new Clutter.Actor({ width: 0, height: 0 });
Main.uiGroup.add_actor(eventHandlerActor);
// We connect to 'event' rather than 'captured-event' because the capturing phase doesn't happen
// when you've grabbed the pointer.
eventHandlerActor.connect('event', (actor, event) => {
return currentDraggable._onEvent(actor, event);
});
}
return eventHandlerActor;
}
function addDragMonitor(monitor) {
dragMonitors.push(monitor);
}
function removeDragMonitor(monitor) {
for (let i = 0; i < dragMonitors.length; i++) {
if (dragMonitors[i] == monitor) {
dragMonitors.splice(i, 1);
return;
}
}
}
var _Draggable = class _Draggable {
constructor(actor, params) {
params = Params.parse(params, { manualMode: false,
restoreOnSuccess: false,
dragActorMaxSize: undefined,
dragActorOpacity: undefined });
this.actor = actor;
this._dragState = DragState.INIT;
if (!params.manualMode) {
this.actor.connect('button-press-event',
this._onButtonPress.bind(this));
this.actor.connect('touch-event',
this._onTouchEvent.bind(this));
}
this.actor.connect('destroy', () => {
this._actorDestroyed = true;
if (this._dragState == DragState.DRAGGING && this._dragCancellable)
this._cancelDrag(global.get_current_time());
this.disconnectAll();
});
this._onEventId = null;
this._touchSequence = null;
this._restoreOnSuccess = params.restoreOnSuccess;
this._dragActorMaxSize = params.dragActorMaxSize;
this._dragActorOpacity = params.dragActorOpacity;
this._buttonDown = false; // The mouse button has been pressed and has not yet been released.
this._animationInProgress = false; // The drag is over and the item is in the process of animating to its original position (snapping back or reverting).
this._dragCancellable = true;
this._eventsGrabbed = false;
this._capturedEventId = 0;
}
_onButtonPress(actor, event) {
if (event.get_button() != 1)
return Clutter.EVENT_PROPAGATE;
this._buttonDown = true;
this._grabActor(event.get_device());
let [stageX, stageY] = event.get_coords();
this._dragStartX = stageX;
this._dragStartY = stageY;
return Clutter.EVENT_PROPAGATE;
}
_onTouchEvent(actor, event) {
// We only handle touch events here on wayland. On X11
// we do get emulated pointer events, which already works
// for single-touch cases. Besides, the X11 passive touch grab
// set up by Mutter will make us see first the touch events
// and later the pointer events, so it will look like two
// unrelated series of events, we want to avoid double handling
// in these cases.
if (!Meta.is_wayland_compositor())
return Clutter.EVENT_PROPAGATE;
if (event.type() != Clutter.EventType.TOUCH_BEGIN ||
!global.display.is_pointer_emulating_sequence(event.get_event_sequence()))
return Clutter.EVENT_PROPAGATE;
this._buttonDown = true;
this._grabActor(event.get_device(), event.get_event_sequence());
let [stageX, stageY] = event.get_coords();
this._dragStartX = stageX;
this._dragStartY = stageY;
return Clutter.EVENT_PROPAGATE;
}
_grabDevice(actor, pointer, touchSequence) {
if (touchSequence)
pointer.sequence_grab(touchSequence, actor);
else if (pointer)
pointer.grab(actor);
this._grabbedDevice = pointer;
this._touchSequence = touchSequence;
this._capturedEventId = global.stage.connect('captured-event', (o, event) => {
let device = event.get_device();
if (device != this._grabbedDevice &&
device.get_device_type() != Clutter.InputDeviceType.KEYBOARD_DEVICE)
return Clutter.EVENT_STOP;
return Clutter.EVENT_PROPAGATE;
});
}
_ungrabDevice() {
if (this._capturedEventId != 0) {
global.stage.disconnect(this._capturedEventId);
this._capturedEventId = 0;
}
if (this._touchSequence)
this._grabbedDevice.sequence_ungrab(this._touchSequence);
else
this._grabbedDevice.ungrab();
this._touchSequence = null;
this._grabbedDevice = null;
}
_grabActor(device, touchSequence) {
this._grabDevice(this.actor, device, touchSequence);
this._onEventId = this.actor.connect('event',
this._onEvent.bind(this));
}
_ungrabActor() {
if (!this._onEventId)
return;
this._ungrabDevice();
this.actor.disconnect(this._onEventId);
this._onEventId = null;
}
_grabEvents(device, touchSequence) {
if (!this._eventsGrabbed) {
this._eventsGrabbed = Main.pushModal(_getEventHandlerActor());
if (this._eventsGrabbed)
this._grabDevice(_getEventHandlerActor(), device, touchSequence);
}
}
_ungrabEvents() {
if (this._eventsGrabbed) {
this._ungrabDevice();
Main.popModal(_getEventHandlerActor());
this._eventsGrabbed = false;
}
}
_eventIsRelease(event) {
if (event.type() == Clutter.EventType.BUTTON_RELEASE) {
let buttonMask = Clutter.ModifierType.BUTTON1_MASK |
Clutter.ModifierType.BUTTON2_MASK |
Clutter.ModifierType.BUTTON3_MASK;
/* We only obey the last button release from the device,
* other buttons may get pressed/released during the DnD op.
*/
return (event.get_state() & buttonMask) == 0;
} else if (event.type() == Clutter.EventType.TOUCH_END) {
/* For touch, we only obey the pointer emulating sequence */
return global.display.is_pointer_emulating_sequence(event.get_event_sequence());
}
return false;
}
_onEvent(actor, event) {
let device = event.get_device();
if (this._grabbedDevice &&
device != this._grabbedDevice &&
device.get_device_type() != Clutter.InputDeviceType.KEYBOARD_DEVICE)
return Clutter.EVENT_PROPAGATE;
// We intercept BUTTON_RELEASE event to know that the button was released in case we
// didn't start the drag, to drop the draggable in case the drag was in progress, and
// to complete the drag and ensure that whatever happens to be under the pointer does
// not get triggered if the drag was cancelled with Esc.
if (this._eventIsRelease(event)) {
this._buttonDown = false;
if (this._dragState == DragState.DRAGGING) {
return this._dragActorDropped(event);
} else if ((this._dragActor != null || this._dragState == DragState.CANCELLED) &&
!this._animationInProgress) {
// Drag must have been cancelled with Esc.
this._dragComplete();
return Clutter.EVENT_STOP;
} else {
// Drag has never started.
this._ungrabActor();
return Clutter.EVENT_PROPAGATE;
}
// We intercept MOTION event to figure out if the drag has started and to draw
// this._dragActor under the pointer when dragging is in progress
} else if (event.type() == Clutter.EventType.MOTION ||
(event.type() == Clutter.EventType.TOUCH_UPDATE &&
global.display.is_pointer_emulating_sequence(event.get_event_sequence()))) {
if (this._dragActor && this._dragState == DragState.DRAGGING)
return this._updateDragPosition(event);
else if (this._dragActor == null && this._dragState != DragState.CANCELLED)
return this._maybeStartDrag(event);
// We intercept KEY_PRESS event so that we can process Esc key press to cancel
// dragging and ignore all other key presses.
} else if (event.type() == Clutter.EventType.KEY_PRESS && this._dragState == DragState.DRAGGING) {
let symbol = event.get_key_symbol();
if (symbol == Clutter.KEY_Escape) {
this._cancelDrag(event.get_time());
return Clutter.EVENT_STOP;
}
}
return Clutter.EVENT_PROPAGATE;
}
/**
* fakeRelease:
*
* Fake a release event.
* Must be called if you want to intercept release events on draggable
* actors for other purposes (for example if you're using
* PopupMenu.ignoreRelease())
*/
fakeRelease() {
this._buttonDown = false;
this._ungrabActor();
}
/**
* startDrag:
* @param {number} stageX: X coordinate of event
* @param {number} stageY: Y coordinate of event
* @param {number} time: Event timestamp
* @param {Clutter.EventSequence=} sequence: Event sequence
* @param {Clutter.InputDevice=} device: device that originated the event
*
* Directly initiate a drag and drop operation from the given actor.
* This function is useful to call if you've specified manualMode
* for the draggable.
*/
startDrag(stageX, stageY, time, sequence, device) {
if (currentDraggable)
return;
if (device == undefined) {
let event = Clutter.get_current_event();
if (event)
device = event.get_device();
if (device == undefined) {
let seat = Clutter.get_default_backend().get_default_seat();
device = seat.get_pointer();
}
}
currentDraggable = this;
this._dragState = DragState.DRAGGING;
// Special-case St.Button: the pointer grab messes with the internal
// state, so force a reset to a reasonable state here
if (this.actor instanceof St.Button) {
this.actor.fake_release();
this.actor.hover = false;
}
this.emit('drag-begin', time);
if (this._onEventId)
this._ungrabActor();
this._grabEvents(device, sequence);
global.display.set_cursor(Meta.Cursor.DND_IN_DRAG);
this._dragX = this._dragStartX = stageX;
this._dragY = this._dragStartY = stageY;
let scaledWidth, scaledHeight;
if (this.actor._delegate && this.actor._delegate.getDragActor) {
this._dragActor = this.actor._delegate.getDragActor();
Main.uiGroup.add_child(this._dragActor);
Main.uiGroup.set_child_above_sibling(this._dragActor, null);
Shell.util_set_hidden_from_pick(this._dragActor, true);
// Drag actor does not always have to be the same as actor. For example drag actor
// can be an image that's part of the actor. So to perform "snap back" correctly we need
// to know what was the drag actor source.
if (this.actor._delegate.getDragActorSource) {
this._dragActorSource = this.actor._delegate.getDragActorSource();
// If the user dragged from the source, then position
// the dragActor over it. Otherwise, center it
// around the pointer
let [sourceX, sourceY] = this._dragActorSource.get_transformed_position();
let x, y;
if (stageX > sourceX && stageX <= sourceX + this._dragActor.width &&
stageY > sourceY && stageY <= sourceY + this._dragActor.height) {
x = sourceX;
y = sourceY;
} else {
x = stageX - this._dragActor.width / 2;
y = stageY - this._dragActor.height / 2;
}
this._dragActor.set_position(x, y);
} else {
this._dragActorSource = this.actor;
}
this._dragOrigParent = undefined;
this._dragOffsetX = this._dragActor.x - this._dragStartX;
this._dragOffsetY = this._dragActor.y - this._dragStartY;
[scaledWidth, scaledHeight] = this._dragActor.get_transformed_size();
} else {
this._dragActor = this.actor;
this._dragActorSource = undefined;
this._dragOrigParent = this.actor.get_parent();
this._dragActorHadFixedPos = this._dragActor.fixed_position_set;
this._dragOrigX = this._dragActor.allocation.x1;
this._dragOrigY = this._dragActor.allocation.y1;
this._dragActorHadNatWidth = this._dragActor.natural_width_set;
this._dragActorHadNatHeight = this._dragActor.natural_height_set;
this._dragOrigWidth = this._dragActor.allocation.get_width();
this._dragOrigHeight = this._dragActor.allocation.get_height();
this._dragOrigScale = this._dragActor.scale_x;
// Ensure actors with an allocation smaller than their natural size
// retain their size
this._dragActor.set_size(...this._dragActor.allocation.get_size());
const transformedExtents = this._dragActor.get_transformed_extents();
this._dragOffsetX = transformedExtents.origin.x - this._dragStartX;
this._dragOffsetY = transformedExtents.origin.y - this._dragStartY;
scaledWidth = transformedExtents.get_width();
scaledHeight = transformedExtents.get_height();
this._dragActor.scale_x = scaledWidth / this._dragOrigWidth;
this._dragActor.scale_y = scaledHeight / this._dragOrigHeight;
this._dragOrigParent.remove_actor(this._dragActor);
Main.uiGroup.add_child(this._dragActor);
Main.uiGroup.set_child_above_sibling(this._dragActor, null);
Shell.util_set_hidden_from_pick(this._dragActor, true);
}
this._dragActorDestroyId = this._dragActor.connect('destroy', () => {
// Cancel ongoing animation (if any)
this._finishAnimation();
this._dragActor = null;
if (this._dragState == DragState.DRAGGING)
this._dragState = DragState.CANCELLED;
});
this._dragOrigOpacity = this._dragActor.opacity;
if (this._dragActorOpacity != undefined)
this._dragActor.opacity = this._dragActorOpacity;
this._snapBackX = this._dragStartX + this._dragOffsetX;
this._snapBackY = this._dragStartY + this._dragOffsetY;
this._snapBackScale = this._dragActor.scale_x;
let origDragOffsetX = this._dragOffsetX;
let origDragOffsetY = this._dragOffsetY;
let [transX, transY] = this._dragActor.get_translation();
this._dragOffsetX -= transX;
this._dragOffsetY -= transY;
this._dragActor.set_position(
this._dragX + this._dragOffsetX,
this._dragY + this._dragOffsetY);
if (this._dragActorMaxSize != undefined) {
let currentSize = Math.max(scaledWidth, scaledHeight);
if (currentSize > this._dragActorMaxSize) {
let scale = this._dragActorMaxSize / currentSize;
let origScale = this._dragActor.scale_x;
// The position of the actor changes as we scale
// around the drag position, but we can't just tween
// to the final position because that tween would
// fight with updates as the user continues dragging
// the mouse; instead we do the position computations in
// a ::new-frame handler.
this._dragActor.ease({
scale_x: scale * origScale,
scale_y: scale * origScale,
duration: SCALE_ANIMATION_TIME,
mode: Clutter.AnimationMode.EASE_OUT_QUAD,
onComplete: () => {
this._updateActorPosition(origScale,
origDragOffsetX, origDragOffsetY, transX, transY);
},
});
this._dragActor.get_transition('scale-x').connect('new-frame', () => {
this._updateActorPosition(origScale,
origDragOffsetX, origDragOffsetY, transX, transY);
});
}
}
}
_updateActorPosition(origScale, origDragOffsetX, origDragOffsetY, transX, transY) {
const currentScale = this._dragActor.scale_x / origScale;
this._dragOffsetX = currentScale * origDragOffsetX - transX;
this._dragOffsetY = currentScale * origDragOffsetY - transY;
this._dragActor.set_position(
this._dragX + this._dragOffsetX,
this._dragY + this._dragOffsetY);
}
_maybeStartDrag(event) {
let [stageX, stageY] = event.get_coords();
// See if the user has moved the mouse enough to trigger a drag
let scaleFactor = St.ThemeContext.get_for_stage(global.stage).scale_factor;
let threshold = St.Settings.get().drag_threshold * scaleFactor;
if (!currentDraggable &&
(Math.abs(stageX - this._dragStartX) > threshold ||
Math.abs(stageY - this._dragStartY) > threshold)) {
this.startDrag(stageX, stageY, event.get_time(), this._touchSequence, event.get_device());
this._updateDragPosition(event);
}
return true;
}
_pickTargetActor() {
return this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
this._dragX, this._dragY);
}
_updateDragHover() {
this._updateHoverId = 0;
let target = this._pickTargetActor();
let dragEvent = {
x: this._dragX,
y: this._dragY,
dragActor: this._dragActor,
source: this.actor._delegate,
targetActor: target,
};
let targetActorDestroyHandlerId;
let handleTargetActorDestroyClosure;
handleTargetActorDestroyClosure = () => {
target = this._pickTargetActor();
dragEvent.targetActor = target;
targetActorDestroyHandlerId =
target.connect('destroy', handleTargetActorDestroyClosure);
};
targetActorDestroyHandlerId =
target.connect('destroy', handleTargetActorDestroyClosure);
for (let i = 0; i < dragMonitors.length; i++) {
let motionFunc = dragMonitors[i].dragMotion;
if (motionFunc) {
let result = motionFunc(dragEvent);
if (result != DragMotionResult.CONTINUE) {
global.display.set_cursor(DRAG_CURSOR_MAP[result]);
return GLib.SOURCE_REMOVE;
}
}
}
dragEvent.targetActor.disconnect(targetActorDestroyHandlerId);
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.display.set_cursor(DRAG_CURSOR_MAP[result]);
return GLib.SOURCE_REMOVE;
}
}
target = target.get_parent();
}
global.display.set_cursor(Meta.Cursor.DND_IN_DRAG);
return GLib.SOURCE_REMOVE;
}
_queueUpdateDragHover() {
if (this._updateHoverId)
return;
this._updateHoverId = GLib.idle_add(GLib.PRIORITY_DEFAULT,
this._updateDragHover.bind(this));
GLib.Source.set_name_by_id(this._updateHoverId, '[gnome-shell] this._updateDragHover');
}
_updateDragPosition(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;
}
_dragActorDropped(event) {
let [dropX, dropY] = event.get_coords();
let target = this._dragActor.get_stage().get_actor_at_pos(Clutter.PickMode.ALL,
dropX, dropY);
// We call observers only once per motion with the innermost
// target actor. If necessary, the observer can walk the
// parent itself.
let dropEvent = {
dropActor: this._dragActor,
targetActor: target,
clutterEvent: event,
};
for (let i = 0; i < dragMonitors.length; i++) {
let dropFunc = dragMonitors[i].dragDrop;
if (dropFunc) {
switch (dropFunc(dropEvent)) {
case DragDropResult.FAILURE:
case DragDropResult.SUCCESS:
return true;
case DragDropResult.CONTINUE:
continue;
}
}
}
// At this point it is too late to cancel a drag by destroying
// the actor, the fate of which is decided by acceptDrop and its
// side-effects
this._dragCancellable = false;
while (target) {
if (target._delegate && target._delegate.acceptDrop) {
let [r_, targX, targY] = target.transform_stage_point(dropX, dropY);
let accepted = false;
try {
accepted = target._delegate.acceptDrop(this.actor._delegate,
this._dragActor, targX, targY, event.get_time());
} catch (e) {
// On error, skip this target
logError(e, "Skipping drag target");
}
if (accepted) {
// If it accepted the drop without taking the actor,
// handle it ourselves.
if (this._dragActor && this._dragActor.get_parent() == Main.uiGroup) {
if (this._restoreOnSuccess) {
this._restoreDragActor(event.get_time());
return true;
} else {
this._dragActor.destroy();
}
}
this._dragState = DragState.INIT;
global.display.set_cursor(Meta.Cursor.DEFAULT);
this.emit('drag-end', event.get_time(), true);
this._dragComplete();
return true;
}
}
target = target.get_parent();
}
this._cancelDrag(event.get_time());
return true;
}
_getRestoreLocation() {
let x, y, scale;
if (this._dragActorSource && this._dragActorSource.visible) {
// Snap the clone back to its source
[x, y] = this._dragActorSource.get_transformed_position();
let [sourceScaledWidth] = this._dragActorSource.get_transformed_size();
scale = sourceScaledWidth ? sourceScaledWidth / this._dragActor.width : 0;
} else if (this._dragOrigParent) {
// Snap the actor back to its original position within
// its parent, adjusting for the fact that the parent
// may have been moved or scaled
let [parentX, parentY] = this._dragOrigParent.get_transformed_position();
let [parentWidth] = this._dragOrigParent.get_size();
let [parentScaledWidth] = this._dragOrigParent.get_transformed_size();
let parentScale = 1.0;
if (parentWidth != 0)
parentScale = parentScaledWidth / parentWidth;
x = parentX + parentScale * this._dragOrigX;
y = parentY + parentScale * this._dragOrigY;
scale = this._dragOrigScale * parentScale;
} else {
// Snap back actor to its original stage position
x = this._snapBackX;
y = this._snapBackY;
scale = this._snapBackScale;
}
return [x, y, scale];
}
_cancelDrag(eventTime) {
this.emit('drag-cancelled', eventTime);
let wasCancelled = this._dragState == DragState.CANCELLED;
this._dragState = DragState.CANCELLED;
if (this._actorDestroyed || wasCancelled) {
global.display.set_cursor(Meta.Cursor.DEFAULT);
if (!this._buttonDown)
this._dragComplete();
this.emit('drag-end', eventTime, false);
if (!this._dragOrigParent && this._dragActor)
this._dragActor.destroy();
return;
}
let [snapBackX, snapBackY, snapBackScale] = this._getRestoreLocation();
this._animateDragEnd(eventTime, {
x: snapBackX,
y: snapBackY,
scale_x: snapBackScale,
scale_y: snapBackScale,
duration: SNAP_BACK_ANIMATION_TIME,
});
}
_restoreDragActor(eventTime) {
this._dragState = DragState.INIT;
let [restoreX, restoreY, restoreScale] = this._getRestoreLocation();
// fade the actor back in at its original location
this._dragActor.set_position(restoreX, restoreY);
this._dragActor.set_scale(restoreScale, restoreScale);
this._dragActor.opacity = 0;
this._animateDragEnd(eventTime, {
duration: REVERT_ANIMATION_TIME,
});
}
_animateDragEnd(eventTime, params) {
this._animationInProgress = true;
// start the animation
this._dragActor.ease(Object.assign(params, {
opacity: this._dragOrigOpacity,
mode: Clutter.AnimationMode.EASE_OUT_QUAD,
onComplete: () => {
this._onAnimationComplete(this._dragActor, eventTime);
},
}));
}
_finishAnimation() {
if (!this._animationInProgress)
return;
this._animationInProgress = false;
if (!this._buttonDown)
this._dragComplete();
global.display.set_cursor(Meta.Cursor.DEFAULT);
}
_onAnimationComplete(dragActor, eventTime) {
if (this._dragOrigParent) {
Main.uiGroup.remove_child(this._dragActor);
this._dragOrigParent.add_actor(this._dragActor);
dragActor.set_scale(this._dragOrigScale, this._dragOrigScale);
if (this._dragActorHadFixedPos)
dragActor.set_position(this._dragOrigX, this._dragOrigY);
else
dragActor.fixed_position_set = false;
if (this._dragActorHadNatWidth)
this._dragActor.set_width(-1);
if (this._dragActorHadNatHeight)
this._dragActor.set_height(-1);
} else {
dragActor.destroy();
}
this.emit('drag-end', eventTime, false);
this._finishAnimation();
}
_dragComplete() {
if (!this._actorDestroyed && this._dragActor)
Shell.util_set_hidden_from_pick(this._dragActor, false);
this._ungrabEvents();
if (this._updateHoverId) {
GLib.source_remove(this._updateHoverId);
this._updateHoverId = 0;
}
if (this._dragActor) {
this._dragActor.disconnect(this._dragActorDestroyId);
this._dragActor = null;
}
this._dragState = DragState.INIT;
currentDraggable = null;
}
};
Signals.addSignalMethods(_Draggable.prototype);
/**
* makeDraggable:
* @param {Clutter.Actor} actor: Source actor
* @param {Object=} params: Additional parameters
* @returns {Object} a new Draggable
*
* Create an object which controls drag and drop for the given actor.
*
* If %manualMode is %true in @params, do not automatically start
* drag and drop on click
*
* If %dragActorMaxSize is present in @params, the drag actor will
* be scaled down to be no larger than that size in pixels.
*
* If %dragActorOpacity is present in @params, the drag actor will
* will be set to have that opacity during the drag.
*
* Note that when the drag actor is the source actor and the drop
* succeeds, the actor scale and opacity aren't reset; if the drop
* target wants to reuse the actor, it's up to the drop target to
* reset these values.
*/
function makeDraggable(actor, params) {
return new _Draggable(actor, params);
}