1 // Copyright (c) 2011 The Native Client Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
6 * @fileoverview Implement a virtual trackball in the tumbler.Trackball
7 * class. This class maps 2D mouse events to 3D rotations by simulating a
8 * trackball that you roll by dragging the mouse. There are two principle
9 * methods in the class: startAtPointInFrame which you use to begin a trackball
10 * simulation and rollToPoint, which you use while dragging the mouse. The
11 * rollToPoint method returns a rotation expressed as a quaternion.
15 // Requires tumbler.Application
16 // Requires tumbler.DragEvent
17 // Requires tumbler.Vector3
20 * Constructor for the Trackball object. This class maps 2D mouse drag events
21 * into 3D rotations by simulating a trackball. The idea is to simulate
22 * clicking on the trackball, and then rolling it as you drag the mouse.
23 * The math behind the trackball is simple: start with a vector from the first
24 * mouse-click on the ball to the center of the 3D view. At the same time, set
25 * the radius of the ball to be the smaller dimension of the 3D view. As you
26 * drag the mouse around in the 3D view, a second vector is computed from the
27 * surface of the ball to the center. The axis of rotation is the cross
28 * product of these two vectors, and the angle of rotation is the angle between
32 tumbler.Trackball = function() {
34 * The square of the trackball's radius. The math never looks at the radius,
35 * but looks at the radius squared.
42 * The 3D vector representing the point on the trackball where the mouse
43 * was clicked. Default is pointing stright through the center of the ball.
47 this.rollStart_ = new tumbler.Vector3(0, 0, 1);
50 * The 2D center of the frame that encloses the trackball.
54 this.center_ = { x: 0, y: 0 };
57 * Cached camera orientation. When a drag START event happens this is set to
58 * the current orientation in the calling view's plugin. The default is the
59 * identity quaternion.
60 * @type {Array.<number>}
63 this.cameraOrientation_ = [0, 0, 0, 1];
67 * Compute the dimensions of the virtual trackball to fit inside |frameSize|.
68 * The radius of the trackball is set to be 1/2 of the smaller of the two frame
69 * dimensions, the center point is at the midpoint of each side.
70 * @param {!goog.math.Size} frameSize 2D-point representing the size of the
71 * element that encloses the virtual trackball.
74 tumbler.Trackball.prototype.initInFrame_ = function(frameSize) {
75 // Compute the radius of the virtual trackball. This is 1/2 of the smaller
76 // of the frame's width and height.
77 var halfFrameSize = 0.5 * Math.min(frameSize.width, frameSize.height);
78 // Cache the square of the trackball's radius.
79 this.sqrRadius_ = halfFrameSize * halfFrameSize;
80 // Figure the center of the view.
81 this.center_.x = frameSize.width * 0.5;
82 this.center_.y = frameSize.height * 0.5;
86 * Method to convert (by translation) a 2D client point from a coordinate space
87 * with origin in the lower-left corner of the client view to a space with
88 * origin in the center of the client view. Use this method before mapping the
89 * 2D point to he 3D tackball point (see also the projectOnTrackball_() method).
90 * Call the startAtPointInFrame before calling this method so that the
91 * |center_| property is correctly initialized.
92 * @param {!Object} clientPoint map this point to the coordinate space with
93 * origin in thecenter of the client view.
94 * @return {Object} the converted point.
97 tumbler.Trackball.prototype.convertClientPoint_ = function(clientPoint) {
98 var difference = { x: clientPoint.x - this.center_.x,
99 y: clientPoint.y - this.center_.y }
104 * Method to map a 2D point to a 3D point on the virtual trackball that was set
105 * up using the startAtPointInFrame method. If the point lies outside of the
106 * radius of the virtual trackball, then the z-coordinate of the 3D point
108 * @param {!Object.<x, y>} point 2D-point in the coordinate space with origin
109 * in the center of the client view.
110 * @return {tumbler.Vector3} the 3D point on the virtual trackball.
113 tumbler.Trackball.prototype.projectOnTrackball_ = function(point) {
114 var sqrRadius2D = point.x * point.x + point.y * point.y;
116 if (sqrRadius2D > this.sqrRadius_) {
117 // |point| lies outside the virtual trackball's sphere, so use a virtual
118 // z-value of 0. This is equivalent to clicking on the horizontal equator
122 // A sphere can be defined as: r^2 = x^2 + y^2 + z^2, so z =
123 // sqrt(r^2 - (x^2 + y^2)).
124 zValue = Math.sqrt(this.sqrRadius_ - sqrRadius2D);
126 var trackballPoint = new tumbler.Vector3(point.x, point.y, zValue);
127 return trackballPoint;
131 * Method to start up the trackball. The trackball works by pretending that a
132 * ball encloses the 3D view. You roll this pretend ball with the mouse. For
133 * example, if you click on the center of the ball and move the mouse straight
134 * to the right, you roll the ball around its Y-axis. This produces a Y-axis
135 * rotation. You can click on the "edge" of the ball and roll it around
136 * in a circle to get a Z-axis rotation.
137 * @param {!Object.<x, y>} startPoint 2D-point, usually the mouse-down
139 * @param {!Object.<width, height>} frameSize 2D-point representing the size of
140 * the element that encloses the virtual trackball.
142 tumbler.Trackball.prototype.startAtPointInFrame =
143 function(startPoint, frameSize) {
144 this.initInFrame_(frameSize);
145 // Compute the starting vector from the surface of the ball to its center.
146 this.rollStart_ = this.projectOnTrackball_(
147 this.convertClientPoint_(startPoint));
151 * Method to roll the virtual trackball; call this in response to a mouseDrag
152 * event. Takes |dragPoint| and projects it from 2D mouse coordinates onto the
153 * virtual track ball that was set up in startAtPointInFrame method.
154 * Returns a quaternion that represents the rotation from |rollStart_| to
156 * @param {!Object.<x, y>} dragPoint 2D-point representing the
157 * destination mouse point.
158 * @return {Array.<number>} a quaternion that represents the rotation from
159 * the point wnere the mouse was clicked on the trackball to this point.
160 * The quaternion looks like this: [[v], cos(angle/2)], where [v] is the
161 * imaginary part of the quaternion and is computed as [x, y, z] *
164 tumbler.Trackball.prototype.rollToPoint = function(dragPoint) {
165 var rollTo = this.convertClientPoint_(dragPoint);
166 if ((Math.abs(this.rollStart_.x - rollTo.x) <
167 tumbler.Trackball.DOUBLE_EPSILON) &&
168 (Math.abs(this.rollStart_.y, rollTo.y) <
169 tumbler.Trackball.DOUBLE_EPSILON)) {
170 // Not enough change in the vectors to roll the ball, return the identity
175 // Compute the ending vector from the surface of the ball to its center.
176 var rollEnd = this.projectOnTrackball_(rollTo);
178 // Take the cross product of the two vectors. r = s X e
179 var rollVector = this.rollStart_.cross(rollEnd);
180 var invStartMag = 1.0 / this.rollStart_.magnitude();
181 var invEndMag = 1.0 / rollEnd.magnitude();
183 // cos(a) = (s . e) / (||s|| ||e||)
184 var cosAng = this.rollStart_.dot(rollEnd) * invStartMag * invEndMag;
185 // sin(a) = ||(s X e)|| / (||s|| ||e||)
186 var sinAng = rollVector.magnitude() * invStartMag * invEndMag;
187 // Build a quaternion that represents the rotation about |rollVector|.
188 // Use atan2 for a better angle. If you use only cos or sin, you only get
189 // half the possible angles, and you can end up with rotations that flip
190 // around near the poles.
191 var rollHalfAngle = Math.atan2(sinAng, cosAng) * 0.5;
192 rollVector.normalize();
193 // The quaternion looks like this: [[v], cos(angle/2)], where [v] is the
194 // imaginary part of the quaternion and is computed as [x, y, z] *
196 rollVector.scale(Math.sin(rollHalfAngle));
197 var ballQuaternion = [rollVector.x,
200 Math.cos(rollHalfAngle)];
201 return ballQuaternion;
205 * Handle the drag START event: grab the current camera orientation from the
206 * sending view and set up the virtual trackball.
207 * @param {!tumbler.Application} view The view controller that called this
209 * @param {!tumbler.DragEvent} dragStartEvent The DRAG_START event that
210 * triggered this handler.
212 tumbler.Trackball.prototype.handleStartDrag =
213 function(controller, dragStartEvent) {
214 // Cache the camera orientation. The orientations from the trackball as it
215 // rolls are concatenated to this orientation and pushed back into the
216 // plugin on the other side of the JavaScript bridge.
217 controller.setCameraOrientation(this.cameraOrientation_);
218 // Invert the y-coordinate for the trackball computations.
219 var frameSize = { width: controller.offsetWidth,
220 height: controller.offsetHeight };
221 var flippedY = { x: dragStartEvent.clientX,
222 y: frameSize.height - dragStartEvent.clientY };
223 this.startAtPointInFrame(flippedY, frameSize);
227 * Handle the drag DRAG event: concatenate the current orientation to the
228 * cached orientation. Send this final value through to the GSPlugin via the
229 * setValueForKey() method.
230 * @param {!tumbler.Application} view The view controller that called this
232 * @param {!tumbler.DragEvent} dragEvent The DRAG event that triggered this
235 tumbler.Trackball.prototype.handleDrag =
236 function(controller, dragEvent) {
237 // Flip the y-coordinate so that the 2D origin is in the lower-left corner.
238 var frameSize = { width: controller.offsetWidth,
239 height: controller.offsetHeight };
240 var flippedY = { x: dragEvent.clientX,
241 y: frameSize.height - dragEvent.clientY };
242 controller.setCameraOrientation(
243 tumbler.multQuaternions(this.rollToPoint(flippedY),
244 this.cameraOrientation_));
248 * Handle the drag END event: get the final orientation and concatenate it to
249 * the cached orientation.
250 * @param {!tumbler.Application} view The view controller that called this
252 * @param {!tumbler.DragEvent} dragEndEvent The DRAG_END event that triggered
255 tumbler.Trackball.prototype.handleEndDrag =
256 function(controller, dragEndEvent) {
257 // Flip the y-coordinate so that the 2D origin is in the lower-left corner.
258 var frameSize = { width: controller.offsetWidth,
259 height: controller.offsetHeight };
260 var flippedY = { x: dragEndEvent.clientX,
261 y: frameSize.height - dragEndEvent.clientY };
262 this.cameraOrientation_ = tumbler.multQuaternions(this.rollToPoint(flippedY),
263 this.cameraOrientation_);
264 controller.setCameraOrientation(this.cameraOrientation_);
268 * A utility function to multiply two quaterions. Returns the product q0 * q1.
269 * This is effectively the same thing as concatenating the two rotations
270 * represented in each quaternion together. Note that quaternion multiplication
271 * is NOT commutative: q0 * q1 != q1 * q0.
272 * @param {!Array.<number>} q0 A 4-element array representing the first
274 * @param {!Array.<number>} q1 A 4-element array representing the second
276 * @return {Array.<number>} A 4-element array representing the product q0 * q1.
278 tumbler.multQuaternions = function(q0, q1) {
279 // Return q0 * q1 (note the order).
281 q0[3] * q1[0] + q0[0] * q1[3] + q0[1] * q1[2] - q0[2] * q1[1],
282 q0[3] * q1[1] - q0[0] * q1[2] + q0[1] * q1[3] + q0[2] * q1[0],
283 q0[3] * q1[2] + q0[0] * q1[1] - q0[1] * q1[0] + q0[2] * q1[3],
284 q0[3] * q1[3] - q0[0] * q1[0] - q0[1] * q1[1] - q0[2] * q1[2]
290 * Real numbers that are less than this distance apart are considered
292 * TODO(dspringer): It seems as though there should be a const like this
293 * in Closure somewhere (goog.math?).
296 tumbler.Trackball.DOUBLE_EPSILON = 1.0e-16;