/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.cooliris.media;
import android.content.Context;
import android.view.MotionEvent;
/**
* Detects transformation gestures involving more than one pointer ("multitouch")
* using the supplied {@link MotionEvent}s. The {@link OnScaleGestureListener}
* callback will notify users when a particular gesture event has occurred.
* This class should only be used with {@link MotionEvent}s reported via touch.
*
* To use this class:
* <ul>
* <li>Create an instance of the {@code ScaleGestureDetector} for your
* {@link View}
* <li>In the {@link View#onTouchEvent(MotionEvent)} method ensure you call
* {@link #onTouchEvent(MotionEvent)}. The methods defined in your
* callback will be executed when the events occur.
* </ul>
* @hide Pending API approval
*/
public class ScaleGestureDetector {
/**
* The listener for receiving notifications when gestures occur.
* If you want to listen for all the different gestures then implement
* this interface. If you only want to listen for a subset it might
* be easier to extend {@link SimpleOnScaleGestureListener}.
*
* An application will receive events in the following order:
* <ul>
* <li>One {@link OnScaleGestureListener#onScaleBegin()}
* <li>Zero or more {@link OnScaleGestureListener#onScale()}
* <li>One {@link OnScaleGestureListener#onTransformEnd()}
* </ul>
*/
public interface OnScaleGestureListener {
/**
* Responds to scaling events for a gesture in progress.
* Reported by pointer motion.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
* @return Whether or not the detector should consider this event
* as handled. If an event was not handled, the detector
* will continue to accumulate movement until an event is
* handled. This can be useful if an application, for example,
* only wants to update scaling factors if the change is
* greater than 0.01.
*/
public boolean onScale(ScaleGestureDetector detector);
/**
* Responds to the beginning of a scaling gesture. Reported by
* new pointers going down.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
* @return Whether or not the detector should continue recognizing
* this gesture. For example, if a gesture is beginning
* with a focal point outside of a region where it makes
* sense, onScaleBegin() may return false to ignore the
* rest of the gesture.
*/
public boolean onScaleBegin(ScaleGestureDetector detector);
/**
* Responds to the end of a scale gesture. Reported by existing
* pointers going up. If the end of a gesture would result in a fling,
* {@link onTransformFling()} is called instead.
*
* Once a scale has ended, {@link ScaleGestureDetector#getFocusX()}
* and {@link ScaleGestureDetector#getFocusY()} will return the location
* of the pointer remaining on the screen.
*
* @param detector The detector reporting the event - use this to
* retrieve extended info about event state.
*/
public void onScaleEnd(ScaleGestureDetector detector);
}
/**
* A convenience class to extend when you only want to listen for a subset
* of scaling-related events. This implements all methods in
* {@link OnScaleGestureListener} but does nothing.
* {@link OnScaleGestureListener#onScale(ScaleGestureDetector)} and
* {@link OnScaleGestureListener#onScaleBegin(ScaleGestureDetector)} return
* {@code true}.
*/
public class SimpleOnScaleGestureListener implements OnScaleGestureListener {
public boolean onScale(ScaleGestureDetector detector) {
return true;
}
public boolean onScaleBegin(ScaleGestureDetector detector) {
return true;
}
public void onScaleEnd(ScaleGestureDetector detector) {
// Intentionally empty
}
}
private static final float PRESSURE_THRESHOLD = 0.67f;
private Context mContext;
private OnScaleGestureListener mListener;
private boolean mGestureInProgress;
private MotionEvent mPrevEvent;
private MotionEvent mCurrEvent;
private float mFocusX;
private float mFocusY;
private float mPrevFingerDiffX;
private float mPrevFingerDiffY;
private float mCurrFingerDiffX;
private float mCurrFingerDiffY;
private float mCurrLen;
private float mPrevLen;
private float mScaleFactor;
private float mCurrPressure;
private float mPrevPressure;
private long mTimeDelta;
public ScaleGestureDetector(Context context, OnScaleGestureListener listener) {
mContext = context;
mListener = listener;
}
public boolean onTouchEvent(MotionEvent event) {
final int action = event.getAction();
boolean handled = true;
if (!mGestureInProgress) {
if ((action == MotionEvent.ACTION_POINTER_1_DOWN ||
action == MotionEvent.ACTION_POINTER_2_DOWN) &&
event.getPointerCount() >= 2) {
// We have a new multi-finger gesture
// Be paranoid in case we missed an event
reset();
mPrevEvent = MotionEvent.obtain(event);
mTimeDelta = 0;
setContext(event);
mGestureInProgress = mListener.onScaleBegin(this);
}
} else {
// Transform gesture in progress - attempt to handle it
switch (action) {
case MotionEvent.ACTION_POINTER_1_UP:
case MotionEvent.ACTION_POINTER_2_UP:
// Gesture ended
setContext(event);
// Set focus point to the remaining finger
int id = (((action & MotionEvent.ACTION_POINTER_ID_MASK)
>> MotionEvent.ACTION_POINTER_ID_SHIFT) == 0) ? 1 : 0;
mFocusX = event.getX(id);
mFocusY = event.getY(id);
mListener.onScaleEnd(this);
mGestureInProgress = false;
reset();
break;
case MotionEvent.ACTION_CANCEL:
mListener.onScaleEnd(this);
mGestureInProgress = false;
reset();
break;
case MotionEvent.ACTION_MOVE:
setContext(event);
// Only accept the event if our relative pressure is within
// a certain limit - this can help filter shaky data as a
// finger is lifted.
if (mCurrPressure / mPrevPressure > PRESSURE_THRESHOLD) {
final boolean updatePrevious = mListener.onScale(this);
if (updatePrevious) {
mPrevEvent.recycle();
mPrevEvent = MotionEvent.obtain(event);
}
}
break;
}
}
return handled;
}
private void setContext(MotionEvent curr) {
if (mCurrEvent != null) {
mCurrEvent.recycle();
}
mCurrEvent = MotionEvent.obtain(curr);
mCurrLen = -1;
mPrevLen = -1;
mScaleFactor = -1;
final MotionEvent prev = mPrevEvent;
final float px0 = prev.getX(0);
final float py0 = prev.getY(0);
final float px1 = prev.getX(1);
final float py1 = prev.getY(1);
final float cx0 = curr.getX(0);
final float cy0 = curr.getY(0);
final float cx1 = curr.getX(1);
final float cy1 = curr.getY(1);
final float pvx = px1 - px0;
final float pvy = py1 - py0;
final float cvx = cx1 - cx0;
final float cvy = cy1 - cy0;
mPrevFingerDiffX = pvx;
mPrevFingerDiffY = pvy;
mCurrFingerDiffX = cvx;
mCurrFingerDiffY = cvy;
mFocusX = cx0 + cvx * 0.5f;
mFocusY = cy0 + cvy * 0.5f;
mTimeDelta = curr.getEventTime() - prev.getEventTime();
mCurrPressure = curr.getPressure(0) + curr.getPressure(1);
mPrevPressure = prev.getPressure(0) + prev.getPressure(1);
}
private void reset() {
if (mPrevEvent != null) {
mPrevEvent.recycle();
mPrevEvent = null;
}
if (mCurrEvent != null) {
mCurrEvent.recycle();
mCurrEvent = null;
}
}
/**
* Returns {@code true} if a two-finger scale gesture is in progress.
* @return {@code true} if a scale gesture is in progress, {@code false} otherwise.
*/
public boolean isInProgress() {
return mGestureInProgress;
}
/**
* Get the X coordinate of the current gesture's focal point.
* If a gesture is in progress, the focal point is directly between
* the two pointers forming the gesture.
* If a gesture is ending, the focal point is the location of the
* remaining pointer on the screen.
* If {@link isInProgress()} would return false, the result of this
* function is undefined.
*
* @return X coordinate of the focal point in pixels.
*/
public float getFocusX() {
return mFocusX;
}
/**
* Get the Y coordinate of the current gesture's focal point.
* If a gesture is in progress, the focal point is directly between
* the two pointers forming the gesture.
* If a gesture is ending, the focal point is the location of the
* remaining pointer on the screen.
* If {@link isInProgress()} would return false, the result of this
* function is undefined.
*
* @return Y coordinate of the focal point in pixels.
*/
public float getFocusY() {
return mFocusY;
}
/**
* Return the current distance between the two pointers forming the
* gesture in progress.
*
* @return Distance between pointers in pixels.
*/
public float getCurrentSpan() {
if (mCurrLen == -1) {
final float cvx = mCurrFingerDiffX;
final float cvy = mCurrFingerDiffY;
mCurrLen = (float)Math.sqrt(cvx*cvx + cvy*cvy);
}
return mCurrLen;
}
/**
* Return the previous distance between the two pointers forming the
* gesture in progress.
*
* @return Previous distance between pointers in pixels.
*/
public float getPreviousSpan() {
if (mPrevLen == -1) {
final float pvx = mPrevFingerDiffX;
final float pvy = mPrevFingerDiffY;
mPrevLen = (float)Math.sqrt(pvx*pvx + pvy*pvy);
}
return mPrevLen;
}
/**
* Return the scaling factor from the previous scale event to the current
* event. This value is defined as
* ({@link getCurrentSpan()} / {@link getPreviousSpan()}).
*
* @return The current scaling factor.
*/
public float getScaleFactor() {
if (mScaleFactor == -1) {
mScaleFactor = getCurrentSpan() / getPreviousSpan();
}
return mScaleFactor;
}
/**
* Return the time difference in milliseconds between the previous
* accepted scaling event and the current scaling event.
*
* @return Time difference since the last scaling event in milliseconds.
*/
public long getTimeDelta() {
return mTimeDelta;
}
/**
* Return the event time of the current event being processed.
*
* @return Current event time in milliseconds.
*/
public long getEventTime() {
return mCurrEvent.getEventTime();
}
}