android 音乐频谱

public class VisualizerView extends View {
// 取得有效数据
int length = 512;
// 线条数(必须为数据的1/4以下)
int index = 128;
// 下落速度
int downspeed = 24;

private byte[] mBytes;
private float[] mPoints;// 当前位置
private float[] mPoints2; // 上一次位置
private float[] upsetPoints;// 倒影

private Paint mForePaint = new Paint();
private Paint upsetPaint = new Paint();// 倒影

public VisualizerView(Context context){
super(context);
init();
}

public VisualizerView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}

private void init() {
LinearGradient mRadialGradient = new LinearGradient(0, 0, 0, 400,new int[] { Color.WHITE, Color.rgb(0, 128, 255) }, null,Shader.TileMode.MIRROR);

mBytes = null;
mForePaint.setStrokeWidth(2f);
mForePaint.setAntiAlias(true);
mForePaint.setShader(mRadialGradient);

upsetPaint.setStrokeWidth(2f);
upsetPaint.setAntiAlias(true);
upsetPaint.setShader(mRadialGradient);
upsetPaint.setAlpha(150);
}

public void updateVisualizer(byte[] bytes) {
mBytes = bytes;
invalidate();
}

@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (mBytes == null || mBytes.length < 3) {
return;
}

byte[] model1 = new byte[length / 2 + 1];
model1[0] = (byte) Math.abs(mBytes[1]);

int j = 1;
for (int i = 2; i < length/4;) {
model1[j] = (byte) Math.hypot(mBytes[i], mBytes[i + 1]);
i += 2;
j++;
}

byte[] model = new byte[length / 2 + 1];
model[0] = (byte) Math.abs(model1[1]);
j = 1;
for (int i = 2; i < length / 2;) {
model[j] = (byte) Math.max(model1[i], model1[i + 1]);
if (j > 0) {
model[j] = (byte) ((model[j] + model[j - 1]) / 2);
}
i += 2;
j++;
}

// 需要画出线条的坐标系
if (mPoints == null || mPoints.length < index * 4) {
mPoints = new float[index * 4];
upsetPoints = new float[index * 4];
mPoints2 = new float[index * 4];
}
for (int i = 0; i < index; i++) {
if (model[i] < 0) {
model[i] = 127;
}
if (model[i] > 127) {
model[i] = 127;
}
float zoom = (float) (14.5 * i / index + 2.5);
if (model[i] < 5) {
zoom = 4;
}

mPoints[i * 4] = getWidth() * i / index;
mPoints[i * 4 + 1] = getHeight() / 3 * 2;
mPoints[i * 4 + 2] = getWidth() * i / index;
mPoints[i * 4 + 3] = 1 + getHeight() / 3 * 2 - model[i] * zoom;

upsetPoints[i * 4] = mPoints[i * 4];
upsetPoints[i * 4 + 1] = mPoints[i * 4 + 1] + 4;
upsetPoints[i * 4 + 2] = mPoints[i * 4 + 2];
upsetPoints[i * 4 + 3] = mPoints[i * 4 + 3] + model[i] * zoom * 3
/ 2;

mPoints2[i * 4] = mPoints[i * 4];
mPoints2[i * 4 + 1] = mPoints[i * 4];
mPoints2[i * 4 + 2] = mPoints[i * 4];
if (mPoints2[i * 4 + 3] > 0 && mPoints[i * 4 + 3] > mPoints2[i * 4 + 3] + downspeed) {
mPoints[i * 4 + 3] = mPoints2[i * 4 + 3] + downspeed;
upsetPoints[i * 4 + 3] = (getHeight() * 2 - mPoints[i * 4 + 3]) / 2 - downspeed / 2;
}
mPoints2[i * 4 + 3] = mPoints[i * 4 + 3];
}
canvas.drawLines(mPoints, mForePaint);
canvas.drawLines(upsetPoints, upsetPaint);
}
}