/*
* 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 android.widget;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.view.animation.AnimationUtils;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;
/**
* This class performs the glow effect used at the edges of scrollable widgets.
* @hide
*/
public class EdgeGlow {
private static final String TAG = "EdgeGlow";
// Time it will take the effect to fully recede in ms
private static final int RECEDE_TIME = 1000;
// Time it will take before a pulled glow begins receding
private static final int PULL_TIME = 167;
// Time it will take for a pulled glow to decay to partial strength before release
private static final int PULL_DECAY_TIME = 1000;
private static final float MAX_ALPHA = 0.8f;
private static final float HELD_EDGE_ALPHA = 0.7f;
private static final float HELD_EDGE_SCALE_Y = 0.5f;
private static final float HELD_GLOW_ALPHA = 0.5f;
private static final float HELD_GLOW_SCALE_Y = 0.5f;
private static final float MAX_GLOW_HEIGHT = 3.f;
private static final float PULL_GLOW_BEGIN = 1.f;
private static final float PULL_EDGE_BEGIN = 0.6f;
// Minimum velocity that will be absorbed
private static final int MIN_VELOCITY = 100;
private static final float EPSILON = 0.001f;
private final Drawable mEdge;
private final Drawable mGlow;
private int mWidth;
private int mHeight;
private float mEdgeAlpha;
private float mEdgeScaleY;
private float mGlowAlpha;
private float mGlowScaleY;
private float mEdgeAlphaStart;
private float mEdgeAlphaFinish;
private float mEdgeScaleYStart;
private float mEdgeScaleYFinish;
private float mGlowAlphaStart;
private float mGlowAlphaFinish;
private float mGlowScaleYStart;
private float mGlowScaleYFinish;
private long mStartTime;
private float mDuration;
private final Interpolator mInterpolator;
private static final int STATE_IDLE = 0;
private static final int STATE_PULL = 1;
private static final int STATE_ABSORB = 2;
private static final int STATE_RECEDE = 3;
private static final int STATE_PULL_DECAY = 4;
// How much dragging should effect the height of the edge image.
// Number determined by user testing.
private static final int PULL_DISTANCE_EDGE_FACTOR = 5;
// How much dragging should effect the height of the glow image.
// Number determined by user testing.
private static final int PULL_DISTANCE_GLOW_FACTOR = 5;
private static final float PULL_DISTANCE_ALPHA_GLOW_FACTOR = 0.8f;
private static final int VELOCITY_EDGE_FACTOR = 8;
private static final int VELOCITY_GLOW_FACTOR = 16;
private int mState = STATE_IDLE;
private float mPullDistance;
public EdgeGlow(Drawable edge, Drawable glow) {
mEdge = edge;
mGlow = glow;
mInterpolator = new DecelerateInterpolator();
}
public void setSize(int width, int height) {
mWidth = width;
mHeight = height;
}
public boolean isFinished() {
return mState == STATE_IDLE;
}
public void finish() {
mState = STATE_IDLE;
}
/**
* Call when the object is pulled by the user.
*
* @param deltaDistance Change in distance since the last call
*/
public void onPull(float deltaDistance) {
final long now = AnimationUtils.currentAnimationTimeMillis();
if (mState == STATE_PULL_DECAY && now - mStartTime < mDuration) {
return;
}
if (mState != STATE_PULL) {
mGlowScaleY = PULL_GLOW_BEGIN;
}
mState = STATE_PULL;
mStartTime = now;
mDuration = PULL_TIME;
mPullDistance += deltaDistance;
float distance = Math.abs(mPullDistance);
mEdgeAlpha = mEdgeAlphaStart = Math.max(PULL_EDGE_BEGIN, Math.min(distance, MAX_ALPHA));
mEdgeScaleY = mEdgeScaleYStart = Math.max(
HELD_EDGE_SCALE_Y, Math.min(distance * PULL_DISTANCE_EDGE_FACTOR, 1.f));
mGlowAlpha = mGlowAlphaStart = Math.min(MAX_ALPHA,
mGlowAlpha +
(Math.abs(deltaDistance) * PULL_DISTANCE_ALPHA_GLOW_FACTOR));
float glowChange = Math.abs(deltaDistance);
if (deltaDistance > 0 && mPullDistance < 0) {
glowChange = -glowChange;
}
if (mPullDistance == 0) {
mGlowScaleY = 0;
}
// Do not allow glow to get larger than MAX_GLOW_HEIGHT.
mGlowScaleY = mGlowScaleYStart = Math.min(MAX_GLOW_HEIGHT, Math.max(
0, mGlowScaleY + glowChange * PULL_DISTANCE_GLOW_FACTOR));
mEdgeAlphaFinish = mEdgeAlpha;
mEdgeScaleYFinish = mEdgeScaleY;
mGlowAlphaFinish = mGlowAlpha;
mGlowScaleYFinish = mGlowScaleY;
}
/**
* Call when the object is released after being pulled.
*/
public void onRelease() {
mPullDistance = 0;
if (mState != STATE_PULL && mState != STATE_PULL_DECAY) {
return;
}
mState = STATE_RECEDE;
mEdgeAlphaStart = mEdgeAlpha;
mEdgeScaleYStart = mEdgeScaleY;
mGlowAlphaStart = mGlowAlpha;
mGlowScaleYStart = mGlowScaleY;
mEdgeAlphaFinish = 0.f;
mEdgeScaleYFinish = 0.f;
mGlowAlphaFinish = 0.f;
mGlowScaleYFinish = 0.f;
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mDuration = RECEDE_TIME;
}
/**
* Call when the effect absorbs an impact at the given velocity.
*
* @param velocity Velocity at impact in pixels per second.
*/
public void onAbsorb(int velocity) {
mState = STATE_ABSORB;
velocity = Math.max(MIN_VELOCITY, Math.abs(velocity));
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mDuration = 0.1f + (velocity * 0.03f);
// The edge should always be at least partially visible, regardless
// of velocity.
mEdgeAlphaStart = 0.f;
mEdgeScaleY = mEdgeScaleYStart = 0.f;
// The glow depends more on the velocity, and therefore starts out
// nearly invisible.
mGlowAlphaStart = 0.5f;
mGlowScaleYStart = 0.f;
// Factor the velocity by 8. Testing on device shows this works best to
// reflect the strength of the user's scrolling.
mEdgeAlphaFinish = Math.max(0, Math.min(velocity * VELOCITY_EDGE_FACTOR, 1));
// Edge should never get larger than the size of its asset.
mEdgeScaleYFinish = Math.max(
HELD_EDGE_SCALE_Y, Math.min(velocity * VELOCITY_EDGE_FACTOR, 1.f));
// Growth for the size of the glow should be quadratic to properly
// respond
// to a user's scrolling speed. The faster the scrolling speed, the more
// intense the effect should be for both the size and the saturation.
mGlowScaleYFinish = Math.min(0.025f + (velocity * (velocity / 100) * 0.00015f), 1.75f);
// Alpha should change for the glow as well as size.
mGlowAlphaFinish = Math.max(
mGlowAlphaStart, Math.min(velocity * VELOCITY_GLOW_FACTOR * .00001f, MAX_ALPHA));
}
/**
* Draw into the provided canvas. Assumes that the canvas has been rotated
* accordingly and the size has been set. The effect will be drawn the full
* width of X=0 to X=width, emitting from Y=0 and extending to some factor <
* 1.f of height.
*
* @param canvas Canvas to draw into
* @return true if drawing should continue beyond this frame to continue the
* animation
*/
public boolean draw(Canvas canvas) {
update();
final int edgeHeight = mEdge.getIntrinsicHeight();
final int glowHeight = mGlow.getIntrinsicHeight();
final float distScale = (float) mHeight / mWidth;
mGlow.setAlpha((int) (Math.max(0, Math.min(mGlowAlpha, 1)) * 255));
// Width of the image should be 3 * the width of the screen.
// Should start off screen to the left.
mGlow.setBounds(-mWidth, 0, mWidth * 2, (int) Math.min(
glowHeight * mGlowScaleY * distScale * 0.6f, mHeight * MAX_GLOW_HEIGHT));
mGlow.draw(canvas);
mEdge.setAlpha((int) (Math.max(0, Math.min(mEdgeAlpha, 1)) * 255));
mEdge.setBounds(0, 0, mWidth, (int) (edgeHeight * mEdgeScaleY));
mEdge.draw(canvas);
return mState != STATE_IDLE;
}
private void update() {
final long time = AnimationUtils.currentAnimationTimeMillis();
final float t = Math.min((time - mStartTime) / mDuration, 1.f);
final float interp = mInterpolator.getInterpolation(t);
mEdgeAlpha = mEdgeAlphaStart + (mEdgeAlphaFinish - mEdgeAlphaStart) * interp;
mEdgeScaleY = mEdgeScaleYStart + (mEdgeScaleYFinish - mEdgeScaleYStart) * interp;
mGlowAlpha = mGlowAlphaStart + (mGlowAlphaFinish - mGlowAlphaStart) * interp;
mGlowScaleY = mGlowScaleYStart + (mGlowScaleYFinish - mGlowScaleYStart) * interp;
if (t >= 1.f - EPSILON) {
switch (mState) {
case STATE_ABSORB:
mState = STATE_RECEDE;
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mDuration = RECEDE_TIME;
mEdgeAlphaStart = mEdgeAlpha;
mEdgeScaleYStart = mEdgeScaleY;
mGlowAlphaStart = mGlowAlpha;
mGlowScaleYStart = mGlowScaleY;
// After absorb, the glow and edge should fade to nothing.
mEdgeAlphaFinish = 0.f;
mEdgeScaleYFinish = 0.f;
mGlowAlphaFinish = 0.f;
mGlowScaleYFinish = 0.f;
break;
case STATE_PULL:
mState = STATE_PULL_DECAY;
mStartTime = AnimationUtils.currentAnimationTimeMillis();
mDuration = PULL_DECAY_TIME;
mEdgeAlphaStart = mEdgeAlpha;
mEdgeScaleYStart = mEdgeScaleY;
mGlowAlphaStart = mGlowAlpha;
mGlowScaleYStart = mGlowScaleY;
// After pull, the glow and edge should fade to nothing.
mEdgeAlphaFinish = 0.f;
mEdgeScaleYFinish = 0.f;
mGlowAlphaFinish = 0.f;
mGlowScaleYFinish = 0.f;
break;
case STATE_PULL_DECAY:
// When receding, we want edge to decrease more slowly
// than the glow.
float factor = mGlowScaleYFinish != 0 ? 1
/ (mGlowScaleYFinish * mGlowScaleYFinish)
: Float.MAX_VALUE;
mEdgeScaleY = mEdgeScaleYStart +
(mEdgeScaleYFinish - mEdgeScaleYStart) *
interp * factor;
mState = STATE_RECEDE;
break;
case STATE_RECEDE:
mState = STATE_IDLE;
break;
}
}
}
}
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