Android动画之旅(四)----小球拟合动画

动画组成:

1.通过三阶贝塞尔曲线来拟合圆,拟合系数的由来,以及怎么选控制点.

2.利用画布canvas.translate,以及scale,rotate的方法,来渐变绘制的过程.

3.熟悉拟合过程.

4.不熟悉的话,先绘制辅助点的移动路线,对理解两个圆的分裂的拟合过程有好处.

package com.example.administrator.animationworkdemo.views;

import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.util.AttributeSet;
import android.view.View;

import java.util.concurrent.CyclicBarrier;

/**
 * 这个例子中，大家可以发现作者的拟合做的并不是很好，连接的地方比较生硬，大家可以思考下如何改善
 * 贝塞尔曲线绘制比较复杂，大家在学习过程中，可以仿照示例中的，将辅助点和线绘制出来，这样会看的更清楚一点
 */
public class BallShapeChangeView extends View {

    // 使用贝塞尔曲线来拟合圆的magic number
    //C 是三阶贝塞尔曲线拟合 圆的 误差最小   获得控制点的参数.
    private static final float C = 0.551915024494f;
    private Paint mPaint;
    private int mRadiusBig = 120, mRadiusSmall = (int) (mRadiusBig / 2f), mWidth, mHeight, mMimWidth = (int) (mRadiusSmall * 2 * 3)/*fill view mim width*/;
    private float mFraction = 0, mFractionDegree = 0, /*degree*/
            mLength, mDistanceBezier;
    private Path mPathCircle, mPathBezier;
    private ValueAnimator mValueAnimator;
    private float[] mPointData = new float[8];// 4个数据点  顺时针排序，从左边开始
    private float[] mPointCtrl = new float[16];// 8个控制点
    private float[] mPos = new float[2];
    private PathMeasure mPathMeasure;
    private Path mPathBezier2;

    public BallShapeChangeView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mPaint = new Paint();
        mPaint.setStyle(Paint.Style.FILL);
        mPaint.setColor(0xFF7C191E);
        mPaint.setAntiAlias(true);
        mPathCircle = new Path();
        mPathBezier = new Path();
        mPathBezier2 = new Path();
        mPathMeasure = new PathMeasure();
        mValueAnimator = ValueAnimator.ofFloat(0, 1, 0);
        mValueAnimator.setDuration(3000);
        mValueAnimator.setRepeatCount(Integer.MAX_VALUE);
        mValueAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                mFraction = (float) animation.getAnimatedValue();
                mFractionDegree = animation.getAnimatedFraction();
                invalidate();
            }
        });
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        // 为了能够更好的控制绘制的大小和位置，当然，初学者写死也是可以的
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        mWidth = MeasureSpec.getSize(widthMeasureSpec);
        mHeight = MeasureSpec.getSize(heightMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (widthMode != MeasureSpec.AT_MOST && heightMode != MeasureSpec.AT_MOST) {
            if (mWidth < mMimWidth)
                mWidth = mMimWidth;
            if (mHeight < mMimWidth)
                mHeight = mMimWidth;
        } else if (widthMeasureSpec != MeasureSpec.AT_MOST) {
            if (mWidth < mMimWidth)
                mWidth = mMimWidth;
        } else if (heightMeasureSpec != MeasureSpec.AT_MOST) {
            if (mHeight < mMimWidth)
                mHeight = mMimWidth;
        }
        setMeasuredDimension(mWidth, mHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        // 通过mFraction来控制绘图的过程，这是常用的一种方式
        canvas.translate(mWidth / 2, mHeight / 2);
        canvas.scale(1, -1);
        canvas.rotate(-360 * mFractionDegree);
        setDoubleCirClePath();
        canvas.drawPath(mPathCircle, mPaint);
        if (mFraction < (1 / 3f)) {// 缩小大圆
            setCirclePath();
            canvas.drawPath(mPathCircle, mPaint);
        } else if (mFraction < 3 / 4f) {// 画贝塞尔曲线
            setBezierPath2();
            canvas.drawPath(mPathBezier, mPaint);
            canvas.drawPath(mPathBezier2, mPaint);
        } else {// 画分离
            //setLastBezierPath();
            //canvas.drawPath(mPathBezier, mPaint);
        }
    }

    private void setDoubleCirClePath() {
        mPathCircle.reset();
        if (mFraction < (1 / 3f)) {
            mPathCircle.addCircle(-mRadiusSmall / 2f * mFraction * 3, 0, mRadiusSmall, Path.Direction.CW);
            mPathCircle.addCircle(mRadiusSmall / 2f * mFraction * 3, 0, mRadiusSmall, Path.Direction.CW);
        } else {
            float distance = (mFraction - 1 / 3f) / (2 / 3f) * (mRadiusSmall * 2 + mRadiusSmall / 2f);
            mPathCircle.addCircle(-mRadiusSmall / 2f - distance, 0, mRadiusSmall, Path.Direction.CW);
            mPathCircle.addCircle(mRadiusSmall / 2f + distance, 0, mRadiusSmall, Path.Direction.CW);
        }
    }

    // mFraction 0 ~ 1/3
    private void setCirclePath() {
        mPointData[0] = -mRadiusBig + mRadiusSmall / 2f * mFraction * 3f;
        mPointData[1] = 0;
        mPointData[2] = 0;
        mPointData[3] = mRadiusBig - mRadiusBig / 2f * mFraction * 3f;//0到1 的三分之一 用来给大圆做效果;
        mPointData[4] = mRadiusBig - mRadiusSmall / 2f * mFraction * 3f;
        mPointData[5] = 0;
        mPointData[6] = mPointData[2];
        mPointData[7] = -mPointData[3];
        mPointCtrl[0] = mPointData[0];// x轴一样
        mPointCtrl[1] = mRadiusBig * C;// y轴向下的
        mPointCtrl[2] = mPointData[2] - mRadiusBig * C;
        mPointCtrl[3] = mPointData[3];// y轴一样
        mPointCtrl[4] = mPointData[2] + mRadiusBig * C;
        mPointCtrl[5] = mPointData[3];
        mPointCtrl[6] = mPointData[4];
        mPointCtrl[7] = mPointCtrl[1];
        mPointCtrl[8] = mPointData[4];
        mPointCtrl[9] = -mPointCtrl[1];
        mPointCtrl[10] = mPointCtrl[4];
        mPointCtrl[11] = mPointData[7];
        mPointCtrl[12] = mPointCtrl[2];
        mPointCtrl[13] = mPointData[7];
        mPointCtrl[14] = mPointData[0];
        mPointCtrl[15] = -mPointCtrl[1];
        mPathCircle.reset();
        mPathCircle.moveTo(mPointData[0], mPointData[1]);
        mPathCircle.cubicTo(mPointCtrl[0], mPointCtrl[1], mPointCtrl[2], mPointCtrl[3], mPointData[2], mPointData[3]);
        mPathCircle.cubicTo(mPointCtrl[4], mPointCtrl[5], mPointCtrl[6], mPointCtrl[7], mPointData[4], mPointData[5]);
        mPathCircle.cubicTo(mPointCtrl[8], mPointCtrl[9], mPointCtrl[10], mPointCtrl[11], mPointData[6], mPointData[7]);
        mPathCircle.cubicTo(mPointCtrl[12], mPointCtrl[13], mPointCtrl[14], mPointCtrl[15], mPointData[0], mPointData[1]);
    }

    // mFraction 1/3 ~ 3/4
    private void setBezierPath2() {
        mPointData[0] = -mRadiusSmall / 2 - (mFraction - 1 / 3f) * mRadiusBig * 2f;
        if (mFraction < 2 / 3f) {
            mPointData[1] = -mRadiusSmall;
        } else {
            mPointData[1] = -mRadiusSmall + (mFraction - 2 / 3f) * 3 * mRadiusSmall;
        }
        if (mFraction < 3 / 4f) {
            mPointData[2] = 0;
        } else {
            //当分裂超过一定程度让结束点的位置变远
            mPointData[2] = (mFraction - 3 / 4f) * 16 * mPointData[0];
        }
        //当动画执行进度大于2/3时,此时该点接近于0
        mPointData[3] = -mRadiusBig + mFraction * mRadiusBig * 1.5f < -0.01f * mRadiusBig ? -mRadiusBig + mFraction * mRadiusBig * 1.5f : 0.01f * -mRadiusBig;

        mPointData[4] = mPointData[2];
        mPointData[5] = -mPointData[3];

        mPointData[6] = mPointData[0];
        mPointData[7] = -mPointData[1];

        mPointCtrl[0] = mPointData[0] + mRadiusSmall;
        mPointCtrl[1] = mPointData[3];

        mPointCtrl[2] = mPointData[0] + mRadiusSmall;
        mPointCtrl[3] = -mPointData[3];

        mPathBezier.reset();
        mPathBezier.moveTo(mPointData[0], mPointData[1]);
        mPathBezier.quadTo(mPointCtrl[0], mPointCtrl[1], mPointData[2], mPointData[3]);
        mPathBezier.lineTo(mPointData[4], mPointData[5]);
        mPathBezier.quadTo(mPointCtrl[2], mPointCtrl[3], mPointData[6], mPointData[7]);

        mPathBezier2.reset();
        mPathBezier2.moveTo(-mPointData[0], mPointData[1]);
        mPathBezier2.quadTo(-mPointCtrl[0], mPointCtrl[1], -mPointData[2], mPointData[3]);
        mPathBezier2.lineTo(-mPointData[4], mPointData[5]);
        mPathBezier2.quadTo(-mPointCtrl[2], mPointCtrl[3], -mPointData[6], mPointData[7]);

    }

    // mFraction 1/3 ~ 3/4
    private void setBezierPath() {
        mPathBezier.reset();
        float distance = (2 * mRadiusSmall + mRadiusSmall / 2f) * mFraction;
        //float topY = mRadiusSmall * (1 - 0.6f * mFraction);
        float topY = mRadiusSmall - mRadiusSmall * (mFraction - 1 / 3f);
        float distanceBezier = topY - distance * C * (0.5f + 0.5f * mFraction);
        if (mDistanceBezier != 0 && distanceBezier < (mDistanceBezier)) {
            distanceBezier = mDistanceBezier;
        }
        mPathBezier.moveTo(-distance, topY);
        mPathBezier.cubicTo(-distance, distanceBezier, distance, distanceBezier, distance, topY);
        if (mDistanceBezier == 0) {
            mPathMeasure.setPath(mPathBezier, false);
            mLength = mPathMeasure.getLength();
            mPathMeasure.getPosTan(mLength / 2, mPos, null);
            if (mPos[1] <= 8) {
                mDistanceBezier = distanceBezier;
                mPathBezier.reset();
                mPathBezier.moveTo(-distance, topY);
                mPathBezier.cubicTo(-distance, mDistanceBezier, distance, mDistanceBezier, distance, topY);
                mPathBezier.lineTo(distance, -topY);
                mPathBezier.cubicTo(distance, -mDistanceBezier, -distance, -mDistanceBezier, -distance, -topY);
                mPathBezier.close();
                return;
            }
        }
        mPathBezier.lineTo(distance, -topY);
        mPathBezier.cubicTo(distance, -distanceBezier, -distance, -distanceBezier, -distance, -topY);
        mPathBezier.close();
    }

    // mFraction 3/4 ~ 1
    private void setLastBezierPath() {
        float x = -mRadiusSmall / 2f - (mFraction - 1 / 3f) / (2 / 3f) * (mRadiusSmall * 2 + mRadiusSmall / 2f);
        mPathBezier.reset();
        mPathBezier.moveTo(x, mRadiusSmall);
        mPathBezier.quadTo(x, 0, x + mRadiusSmall + mRadiusSmall * (4 - mFraction * 4), 0);
        mPathBezier.quadTo(x, 0, x, -mRadiusSmall);
        mPathBezier.lineTo(x, mRadiusSmall);
        mPathBezier.moveTo(-x, mRadiusSmall);
        mPathBezier.quadTo(-x, 0, -x - mRadiusSmall - mRadiusSmall * (4 - mFraction * 4), 0);
        mPathBezier.quadTo(-x, 0, -x, -mRadiusSmall);
        mPathBezier.lineTo(-x, mRadiusSmall);
        mPathBezier.close();
    }


    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (!mValueAnimator.isRunning())
            mValueAnimator.start();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mValueAnimator.isRunning())
            mValueAnimator.cancel();
    }
}