贝塞尔曲线绘制波浪

效果图：

关于贝塞尔曲线的介绍可以参照文章

https://www.cnblogs.com/wjtaigwh/p/6647114.html

了解完贝塞尔曲线就来完成波浪自定义View

大体思路就是先绘制一条超出屏幕长的二阶贝塞尔曲线，然后再动画循环平移曲线。

package com.xingyun.waveapplication;

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

/**
 * Created by SY on 2018/5/1.
 */

public class WaveView1 extends View {
private int width = 0;
private int height = 0;
private int baseHeight = 0;// 波浪高度
private int waveHeight = 200;// 波峰波、波谷高度
private int waveWidth;//波浪宽度
private float offset = 0;//偏移量
private Paint paint;


public WaveView1(Context context, AttributeSet attrs) {
    super(context, attrs);
    initPaint();
}

/**
 * 设置开启动画
 */
private void startAni() {
    ValueAnimator animator = ValueAnimator.ofFloat(0, waveWidth);
    animator.setInterpolator(new LinearInterpolator());
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            float animatorValue = (float) animation.getAnimatedValue();
            offset = animatorValue;
            postInvalidate();
        }
    });
    animator.setDuration(1000);
    animator.setRepeatCount(ValueAnimator.INFINITE);
    animator.start();
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.drawPath(getPath(), paint);
}

//初始化paint
private void initPaint() {
    paint = new Paint();
    paint.setColor(Color.parseColor("#88FFFFFF"));
    paint.setStyle(Paint.Style.FILL);
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    super.onLayout(changed, left, top, right, bottom);
    width = getMeasuredWidth();
    height = getMeasuredHeight();
    waveWidth = width;
    baseHeight = height / 2;
    startAni();
}


/**
 * 生成path
 *
 * @return
 */
private Path getPath() {
    int itemWidth = waveWidth / 2;//波长
    Path path = new Path();
    path.moveTo(-itemWidth * 3 , baseHeight);//起始点坐标
    for (int count = -3; count < 2; count++) {
        int controlX = count * itemWidth;
        path.quadTo(controlX + itemWidth / 2 + offset,//控制点的X
                getWaveHeight(count),//控制点的Y
                controlX + itemWidth + offset,//结束点的X
                baseHeight//结束点的Y
        );
    }
    //封闭区域
    path.lineTo(width, height);
    path.lineTo(0, height);
    path.close();
    return path;
}

//计算波峰、波谷
private int getWaveHeight(int num) {
    if (num % 2 == 0) {
        return baseHeight - waveHeight;
    }
    return baseHeight + waveHeight;
}

}

初始化画笔之后再onLayout方法获取宽高，然后ondraw方法里绘制关键的曲线。通过getPath方法得到曲线的path。通过path.moveTo方法设置起始点坐标，调用path.quadTo绘制曲线，quadTo四个参数分别为控制点的XY坐标和结束点的XY坐标。完成后调用path.lineTo连接屏幕底部，将区域封闭起来。其中控制点Y坐标为一上一下交替，通过 getWaveHeight方法判断是波峰还是波谷。这样波浪曲线就绘制完成了。最后只要设置动画不断重绘并且循环动画就完成了。