Java tutorial
/* * Copyright (C) 2017 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.support.graphics.drawable; import static android.support.annotation.RestrictTo.Scope.LIBRARY_GROUP; import static java.lang.Math.abs; import static java.lang.Math.min; import android.content.Context; import android.content.res.Resources; import android.content.res.TypedArray; import android.graphics.Path; import android.graphics.PathMeasure; import android.support.annotation.RestrictTo; import android.support.v4.content.res.TypedArrayUtils; import android.support.v4.graphics.PathParser; import android.util.AttributeSet; import android.view.InflateException; import android.view.animation.Interpolator; import org.xmlpull.v1.XmlPullParser; /** * 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> * @hide */ @RestrictTo(LIBRARY_GROUP) public class PathInterpolatorCompat implements Interpolator { // This governs how accurate the approximation of the Path is. private static final float PRECISION = 0.002f; public static final int MAX_NUM_POINTS = 3000; public static final double EPSILON = 0.00001; private float[] mX; // x coordinates in the line private float[] mY; // y coordinates in the line public PathInterpolatorCompat(Context context, AttributeSet attrs, XmlPullParser parser) { this(context.getResources(), context.getTheme(), attrs, parser); } public PathInterpolatorCompat(Resources res, Resources.Theme theme, AttributeSet attrs, XmlPullParser parser) { TypedArray a = TypedArrayUtils.obtainAttributes(res, theme, attrs, AndroidResources.STYLEABLE_PATH_INTERPOLATOR); parseInterpolatorFromTypeArray(a, parser); a.recycle(); } private void parseInterpolatorFromTypeArray(TypedArray a, XmlPullParser parser) { // If there is pathData defined in the xml file, then the controls points // will be all coming from pathData. if (TypedArrayUtils.hasAttribute(parser, "pathData")) { String pathData = TypedArrayUtils.getNamedString(a, parser, "pathData", AndroidResources.STYLEABLE_PATH_INTERPOLATOR_PATH_DATA); Path path = PathParser.createPathFromPathData(pathData); if (path == null) { throw new InflateException("The path is null, which is created" + " from " + pathData); } initPath(path); } else { if (!TypedArrayUtils.hasAttribute(parser, "controlX1")) { throw new InflateException("pathInterpolator requires the controlX1 attribute"); } else if (!TypedArrayUtils.hasAttribute(parser, "controlY1")) { throw new InflateException("pathInterpolator requires the controlY1 attribute"); } float x1 = TypedArrayUtils.getNamedFloat(a, parser, "controlX1", AndroidResources.STYLEABLE_PATH_INTERPOLATOR_CONTROL_X_1, 0); float y1 = TypedArrayUtils.getNamedFloat(a, parser, "controlY1", AndroidResources.STYLEABLE_PATH_INTERPOLATOR_CONTROL_Y_1, 0); boolean hasX2 = TypedArrayUtils.hasAttribute(parser, "controlX2"); boolean hasY2 = TypedArrayUtils.hasAttribute(parser, "controlY2"); if (hasX2 != hasY2) { throw new InflateException( "pathInterpolator requires both controlX2 and" + " controlY2 for cubic Beziers."); } if (!hasX2) { initQuad(x1, y1); } else { float x2 = TypedArrayUtils.getNamedFloat(a, parser, "controlX2", AndroidResources.STYLEABLE_PATH_INTERPOLATOR_CONTROL_X_2, 0); float y2 = TypedArrayUtils.getNamedFloat(a, parser, "controlY2", AndroidResources.STYLEABLE_PATH_INTERPOLATOR_CONTROL_Y_2, 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) { final PathMeasure pathMeasure = new PathMeasure(path, false /* forceClosed */); final float pathLength = pathMeasure.getLength(); final int numPoints = min(MAX_NUM_POINTS, (int) (pathLength / PRECISION) + 1); if (numPoints <= 0) { throw new IllegalArgumentException("The Path has a invalid length " + pathLength); } mX = new float[numPoints]; mY = new float[numPoints]; final float[] position = new float[2]; for (int i = 0; i < numPoints; ++i) { final float distance = (i * pathLength) / (numPoints - 1); pathMeasure.getPosTan(distance, position, null /* tangent */); mX[i] = position[0]; mY[i] = position[1]; } if (abs(mX[0]) > EPSILON || abs(mY[0]) > EPSILON || abs(mX[numPoints - 1] - 1) > EPSILON || abs(mY[numPoints - 1] - 1) > EPSILON) { throw new IllegalArgumentException("The Path must start at (0,0) and end at (1,1)" + " start: " + mX[0] + "," + mY[0] + " end:" + mX[numPoints - 1] + "," + mY[numPoints - 1]); } float prevX = 0; int componentIndex = 0; for (int i = 0; i < numPoints; i++) { float x = mX[componentIndex++]; if (x < prevX) { throw new IllegalArgumentException("The Path cannot loop back on itself, x :" + x); } mX[i] = x; prevX = x; } if (pathMeasure.nextContour()) { throw new IllegalArgumentException("The Path should be continuous," + " can't have 2+ contours"); } } /** * 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)); } }