Java tutorial
/* * Copyright (C) 2013 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.view.animation; import android.content.Context; import android.content.res.Resources; import android.content.res.Resources.Theme; import android.content.res.TypedArray; import android.graphics.Path; import android.util.AttributeSet; import android.util.PathParser; import android.view.InflateException; import com.android.internal.R; import com.android.internal.view.animation.HasNativeInterpolator; import com.android.internal.view.animation.NativeInterpolatorFactory; import com.android.internal.view.animation.NativeInterpolatorFactoryHelper; /** * An interpolator that can traverse a Path that extends from <code>Point</code> * <code>(0, 0)</code> to <code>(1, 1)</code>. The x coordinate along the <code>Path</code> * is the input value and the output is the y coordinate of the line at that point. * This means that the Path must conform to a function <code>y = f(x)</code>. * * <p>The <code>Path</code> must not have gaps in the x direction and must not * loop back on itself such that there can be two points sharing the same x coordinate. * It is alright to have a disjoint line in the vertical direction:</p> * <p><blockquote><pre> * Path path = new Path(); * path.lineTo(0.25f, 0.25f); * path.moveTo(0.25f, 0.5f); * path.lineTo(1f, 1f); * </pre></blockquote></p> */ @HasNativeInterpolator public class PathInterpolator extends BaseInterpolator implements NativeInterpolatorFactory { // This governs how accurate the approximation of the Path is. private static final float PRECISION = 0.002f; private float[] mX; // x coordinates in the line private float[] mY; // y coordinates in the line /** * Create an interpolator for an arbitrary <code>Path</code>. The <code>Path</code> * must begin at <code>(0, 0)</code> and end at <code>(1, 1)</code>. * * @param path The <code>Path</code> to use to make the line representing the interpolator. */ public PathInterpolator(Path path) { initPath(path); } /** * Create an interpolator for a quadratic Bezier curve. The end points * <code>(0, 0)</code> and <code>(1, 1)</code> are assumed. * * @param controlX The x coordinate of the quadratic Bezier control point. * @param controlY The y coordinate of the quadratic Bezier control point. */ public PathInterpolator(float controlX, float controlY) { initQuad(controlX, controlY); } /** * Create an interpolator for a cubic Bezier curve. The end points * <code>(0, 0)</code> and <code>(1, 1)</code> are assumed. * * @param controlX1 The x coordinate of the first control point of the cubic Bezier. * @param controlY1 The y coordinate of the first control point of the cubic Bezier. * @param controlX2 The x coordinate of the second control point of the cubic Bezier. * @param controlY2 The y coordinate of the second control point of the cubic Bezier. */ public PathInterpolator(float controlX1, float controlY1, float controlX2, float controlY2) { initCubic(controlX1, controlY1, controlX2, controlY2); } public PathInterpolator(Context context, AttributeSet attrs) { this(context.getResources(), context.getTheme(), attrs); } /** @hide */ public PathInterpolator(Resources res, Theme theme, AttributeSet attrs) { TypedArray a; if (theme != null) { a = theme.obtainStyledAttributes(attrs, R.styleable.PathInterpolator, 0, 0); } else { a = res.obtainAttributes(attrs, R.styleable.PathInterpolator); } parseInterpolatorFromTypeArray(a); setChangingConfiguration(a.getChangingConfigurations()); a.recycle(); } private void parseInterpolatorFromTypeArray(TypedArray a) { // If there is pathData defined in the xml file, then the controls points // will be all coming from pathData. if (a.hasValue(R.styleable.PathInterpolator_pathData)) { String pathData = a.getString(R.styleable.PathInterpolator_pathData); Path path = PathParser.createPathFromPathData(pathData); if (path == null) { throw new InflateException("The path is null, which is created" + " from " + pathData); } initPath(path); } else { if (!a.hasValue(R.styleable.PathInterpolator_controlX1)) { throw new InflateException("pathInterpolator requires the controlX1 attribute"); } else if (!a.hasValue(R.styleable.PathInterpolator_controlY1)) { throw new InflateException("pathInterpolator requires the controlY1 attribute"); } float x1 = a.getFloat(R.styleable.PathInterpolator_controlX1, 0); float y1 = a.getFloat(R.styleable.PathInterpolator_controlY1, 0); boolean hasX2 = a.hasValue(R.styleable.PathInterpolator_controlX2); boolean hasY2 = a.hasValue(R.styleable.PathInterpolator_controlY2); if (hasX2 != hasY2) { throw new InflateException( "pathInterpolator requires both controlX2 and controlY2 for cubic Beziers."); } if (!hasX2) { initQuad(x1, y1); } else { float x2 = a.getFloat(R.styleable.PathInterpolator_controlX2, 0); float y2 = a.getFloat(R.styleable.PathInterpolator_controlY2, 0); initCubic(x1, y1, x2, y2); } } } private void initQuad(float controlX, float controlY) { Path path = new Path(); path.moveTo(0, 0); path.quadTo(controlX, controlY, 1f, 1f); initPath(path); } private void initCubic(float x1, float y1, float x2, float y2) { Path path = new Path(); path.moveTo(0, 0); path.cubicTo(x1, y1, x2, y2, 1f, 1f); initPath(path); } private void initPath(Path path) { float[] pointComponents = path.approximate(PRECISION); int numPoints = pointComponents.length / 3; if (pointComponents[1] != 0 || pointComponents[2] != 0 || pointComponents[pointComponents.length - 2] != 1 || pointComponents[pointComponents.length - 1] != 1) { throw new IllegalArgumentException("The Path must start at (0,0) and end at (1,1)"); } mX = new float[numPoints]; mY = new float[numPoints]; float prevX = 0; float prevFraction = 0; int componentIndex = 0; for (int i = 0; i < numPoints; i++) { float fraction = pointComponents[componentIndex++]; float x = pointComponents[componentIndex++]; float y = pointComponents[componentIndex++]; if (fraction == prevFraction && x != prevX) { throw new IllegalArgumentException("The Path cannot have discontinuity in the X axis."); } if (x < prevX) { throw new IllegalArgumentException("The Path cannot loop back on itself."); } mX[i] = x; mY[i] = y; prevX = x; prevFraction = fraction; } } /** * Using the line in the Path in this interpolator that can be described as * <code>y = f(x)</code>, finds the y coordinate of the line given <code>t</code> * as the x coordinate. Values less than 0 will always return 0 and values greater * than 1 will always return 1. * * @param t Treated as the x coordinate along the line. * @return The y coordinate of the Path along the line where x = <code>t</code>. * @see Interpolator#getInterpolation(float) */ @Override public float getInterpolation(float t) { if (t <= 0) { return 0; } else if (t >= 1) { return 1; } // Do a binary search for the correct x to interpolate between. int startIndex = 0; int endIndex = mX.length - 1; while (endIndex - startIndex > 1) { int midIndex = (startIndex + endIndex) / 2; if (t < mX[midIndex]) { endIndex = midIndex; } else { startIndex = midIndex; } } float xRange = mX[endIndex] - mX[startIndex]; if (xRange == 0) { return mY[startIndex]; } float tInRange = t - mX[startIndex]; float fraction = tInRange / xRange; float startY = mY[startIndex]; float endY = mY[endIndex]; return startY + (fraction * (endY - startY)); } /** @hide **/ @Override public long createNativeInterpolator() { return NativeInterpolatorFactoryHelper.createPathInterpolator(mX, mY); } }