/*
* Copyright (C) 2008 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 android.graphics.drawable;
import android.content.res.Resources;
import android.graphics.Canvas;
import android.os.SystemClock;
/**
* An extension of LayerDrawables that is intended to cross-fade between
* the first and second layer. To start the transition, call {@link #startTransition(int)}. To
* display just the first layer, call {@link #resetTransition()}.
* <p>
* It can be defined in an XML file with the <code><transition></code> element.
* Each Drawable in the transition is defined in a nested <code><item></code>. For more
* information, see the guide to <a
* href="{@docRoot}guide/topics/resources/drawable-resource.html">Drawable Resources</a>.</p>
*
* @attr ref android.R.styleable#LayerDrawableItem_left
* @attr ref android.R.styleable#LayerDrawableItem_top
* @attr ref android.R.styleable#LayerDrawableItem_right
* @attr ref android.R.styleable#LayerDrawableItem_bottom
* @attr ref android.R.styleable#LayerDrawableItem_drawable
* @attr ref android.R.styleable#LayerDrawableItem_id
*
*/
public class TransitionDrawable extends LayerDrawable implements Drawable.Callback {
/**
* A transition is about to start.
*/
private static final int TRANSITION_STARTING = 0;
/**
* The transition has started and the animation is in progress
*/
private static final int TRANSITION_RUNNING = 1;
/**
* No transition will be applied
*/
private static final int TRANSITION_NONE = 2;
/**
* The current state of the transition. One of {@link #TRANSITION_STARTING},
* {@link #TRANSITION_RUNNING} and {@link #TRANSITION_NONE}
*/
private int mTransitionState = TRANSITION_NONE;
private boolean mReverse;
private long mStartTimeMillis;
private int mFrom;
private int mTo;
private int mDuration;
private int mOriginalDuration;
private int mAlpha = 0;
private boolean mCrossFade;
/**
* Create a new transition drawable with the specified list of layers. At least
* 2 layers are required for this drawable to work properly.
*/
public TransitionDrawable(Drawable[] layers) {
this(new TransitionState(null, null, null), layers);
}
/**
* Create a new transition drawable with no layer. To work correctly, at least 2
* layers must be added to this drawable.
*
* @see #TransitionDrawable(Drawable[])
*/
TransitionDrawable() {
this(new TransitionState(null, null, null), (Resources) null);
}
private TransitionDrawable(TransitionState state, Resources res) {
super(state, res);
}
private TransitionDrawable(TransitionState state, Drawable[] layers) {
super(layers, state);
}
@Override
LayerState createConstantState(LayerState state, Resources res) {
return new TransitionState((TransitionState) state, this, res);
}
/**
* Begin the second layer on top of the first layer.
*
* @param durationMillis The length of the transition in milliseconds
*/
public void startTransition(int durationMillis) {
mFrom = 0;
mTo = 255;
mAlpha = 0;
mDuration = mOriginalDuration = durationMillis;
mReverse = false;
mTransitionState = TRANSITION_STARTING;
invalidateSelf();
}
/**
* Show only the first layer.
*/
public void resetTransition() {
mAlpha = 0;
mTransitionState = TRANSITION_NONE;
invalidateSelf();
}
/**
* Reverses the transition, picking up where the transition currently is.
* If the transition is not currently running, this will start the transition
* with the specified duration. If the transition is already running, the last
* known duration will be used.
*
* @param duration The duration to use if no transition is running.
*/
public void reverseTransition(int duration) {
final long time = SystemClock.uptimeMillis();
// Animation is over
if (time - mStartTimeMillis > mDuration) {
if (mTo == 0) {
mFrom = 0;
mTo = 255;
mAlpha = 0;
mReverse = false;
} else {
mFrom = 255;
mTo = 0;
mAlpha = 255;
mReverse = true;
}
mDuration = mOriginalDuration = duration;
mTransitionState = TRANSITION_STARTING;
invalidateSelf();
return;
}
mReverse = !mReverse;
mFrom = mAlpha;
mTo = mReverse ? 0 : 255;
mDuration = (int) (mReverse ? time - mStartTimeMillis :
mOriginalDuration - (time - mStartTimeMillis));
mTransitionState = TRANSITION_STARTING;
}
@Override
public void draw(Canvas canvas) {
boolean done = true;
switch (mTransitionState) {
case TRANSITION_STARTING:
mStartTimeMillis = SystemClock.uptimeMillis();
done = false;
mTransitionState = TRANSITION_RUNNING;
break;
case TRANSITION_RUNNING:
if (mStartTimeMillis >= 0) {
float normalized = (float)
(SystemClock.uptimeMillis() - mStartTimeMillis) / mDuration;
done = normalized >= 1.0f;
normalized = Math.min(normalized, 1.0f);
mAlpha = (int) (mFrom + (mTo - mFrom) * normalized);
}
break;
}
final int alpha = mAlpha;
final boolean crossFade = mCrossFade;
final ChildDrawable[] array = mLayerState.mChildren;
if (done) {
// the setAlpha() calls below trigger invalidation and redraw. If we're done, just draw
// the appropriate drawable[s] and return
if (!crossFade || alpha == 0) {
array[0].mDrawable.draw(canvas);
}
if (alpha == 0xFF) {
array[1].mDrawable.draw(canvas);
}
return;
}
Drawable d;
d = array[0].mDrawable;
if (crossFade) {
d.setAlpha(255 - alpha);
}
d.draw(canvas);
if (crossFade) {
d.setAlpha(0xFF);
}
if (alpha > 0) {
d = array[1].mDrawable;
d.setAlpha(alpha);
d.draw(canvas);
d.setAlpha(0xFF);
}
if (!done) {
invalidateSelf();
}
}
/**
* Enables or disables the cross fade of the drawables. When cross fade
* is disabled, the first drawable is always drawn opaque. With cross
* fade enabled, the first drawable is drawn with the opposite alpha of
* the second drawable. Cross fade is disabled by default.
*
* @param enabled True to enable cross fading, false otherwise.
*/
public void setCrossFadeEnabled(boolean enabled) {
mCrossFade = enabled;
}
/**
* Indicates whether the cross fade is enabled for this transition.
*
* @return True if cross fading is enabled, false otherwise.
*/
public boolean isCrossFadeEnabled() {
return mCrossFade;
}
static class TransitionState extends LayerState {
TransitionState(TransitionState orig, TransitionDrawable owner, Resources res) {
super(orig, owner, res);
}
@Override
public Drawable newDrawable() {
return new TransitionDrawable(this, (Resources) null);
}
@Override
public Drawable newDrawable(Resources res) {
return new TransitionDrawable(this, res);
}
@Override
public int getChangingConfigurations() {
return mChangingConfigurations;
}
}
}
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