Android实现波浪效果 - WaveView

先上效果图
WaveView截图

实现

WaveView的属性

Wate Level(水位): 波浪静止时水面距离底部的高度
Amplitude(振幅): 波浪垂直振动时偏离水面的最大距离
Wave Length(波长): 一个完整的波浪的水平长度
Wave Shift(偏移): 波浪相对于初始位置的水平偏移

实现思路

设想我们有一个画好波形的图片，那么我们只需要用这张图片填充（X轴方向重复，Y轴方向延伸）整个View，然后水平移动图片，就可以得到波浪效果了。

所以要做的事很简单：绘制一个波形图，填充到View里，移动波形图。

1. 绘制初始波形

private void createShader() {
    ...
    Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    // Draw default waves into the bitmap
    // y=Asin(ωx+φ)+h
    float waveX1 = 0;
    final float wave2Shift = mDefaultWaveLength / 4;
    final float endX = getWidth();
    final float endY = getHeight();
    ...
    while (waveX1 < endX) {
        double wx = waveX1 * mDefaultAngularFrequency;
        int startY = (int) (mDefaultWaterLevel + mDefaultAmplitude * Math.sin(wx));
        // draw bottom wave with the alpha 40
        canvas.drawLine(waveX1, startY, waveX1, endY, wavePaint1);
        // draw top wave with the alpha 60
        float waveX2 = (waveX1 + wave2Shift) % endX;
        canvas.drawLine(waveX2, startY, waveX2, endY, wavePaint2);
        waveX1++;
    }
    // use the bitamp to create the shader
    mWaveShader = new BitmapShader(bitmap, Shader.TileMode.REPEAT, Shader.TileMode.CLAMP);
    mViewPaint.setShader(mWaveShader);
}

首先一个长宽恰等于WaveView的Bitmap：Bitmap.createBitmap(getWidth(), getHeight(), Bitmap.Config.ARGB_8888)。

在Bitmap中使用默认的属性绘制出初始波形。初始波形的属性：Wate Level(水位)为WaveView高度的1/2；Amplitude(振幅)为WaveView高度的1/20；Wave Length(波长)等于WaveView的宽度。

绘制好的初始波形是下面这个样子：

初始波形

代码第 9 ~ 27 行进行初始波形的绘制。波形由wave1和wave2两个波组成，wave2就是wave1向左偏移1/4的wave length，所以不需要重复计算。

最后把这个Bitmap设置成为Paint的Shader。设置Shader相当于设定画笔的形状，使用设置了Shader的Paint绘制图形时，实际上是在使用Bitmap填充绘制的区域。X轴的填充方式为TileMode.REPEAT，即重复填充；Y轴的填充方式为TileMode.CLAMP，即使用边缘的色值延伸填充。

2. 调整Bitmap的大小并填充到WaveView

有了初始波形，当WaveView的属性改变时，只需要对初始波形进行相应的拉伸/压缩和位移就可以得到用户想要的波形。

// sacle shader according to mWaveLengthRatio and mAmplitudeRatio
// this decides the size(mWaveLengthRatio for width, mAmplitudeRatio for height) of waves
mShaderMatrix.setScale(
        mWaveLengthRatio / DEFAULT_WAVE_LENGTH_RATIO,
        mAmplitudeRatio / DEFAULT_AMPLITUDE_RATIO,
        0,
        mDefaultWaterLevel);
// translate shader according to mWaveShiftRatio and mWaterLevelRatio this decides the start position(mWaveShiftRatio for x, mWaterLevelRatio for 
// this decides the start position(mWaveShiftRatio for x, mWaterLevelRatio for y) of waves
mShaderMatrix.postTranslate(
        mWaveShiftRatio * getWidth(),
        (DEFAULT_WATER_LEVEL_RATIO - mWaterLevelRatio) * getHeight());
// assign matrix to invalidate the shader
mWaveShader.setLocalMatrix(mShaderMatrix);
float radius = getWidth() / 2f
        - (mBorderPaint == null ? 0f : mBorderPaint.getStrokeWidth());
canvas.drawCircle(getWidth() / 2f, getHeight() / 2f, radius, mViewPaint);

代码 3 ~ 6 行对Shader进行拉伸/压缩，10 ~ 12 行对Shader进行水平/竖直平移。

代码 17 ~ 19 行用Shader填充成想要的形状。

3. 动画

// horizontal animation.
// wave waves infinitely.
ObjectAnimator waveShiftAnim = ObjectAnimator.ofFloat(
        mWaveView, "waveShiftRatio", 0f, 1f);
waveShiftAnim.setRepeatCount(ValueAnimator.INFINITE);
waveShiftAnim.setDuration(1000);
waveShiftAnim.setInterpolator(new LinearInterpolator());
animators.add(waveShiftAnim);
// vertical animation.
// water level increases from 0 to center of WaveView
ObjectAnimator waterLevelAnim = ObjectAnimator.ofFloat(
        mWaveView, "waterLevelRatio", 0f, 0.5f);
waterLevelAnim.setDuration(10000);
waterLevelAnim.setInterpolator(new DecelerateInterpolator());
animators.add(waterLevelAnim);
// amplitude animation.
// wave grows big then grows small, repeatedly
ObjectAnimator amplitudeAnim = ObjectAnimator.ofFloat(
        mWaveView, "amplitudeRatio", 0f, 0.05f);
amplitudeAnim.setRepeatCount(ValueAnimator.INFINITE);
amplitudeAnim.setRepeatMode(ValueAnimator.REVERSE);
amplitudeAnim.setDuration(5000);
amplitudeAnim.setInterpolator(new LinearInterpolator());
animators.add(amplitudeAnim);