在Android上用Canvas绘制音频波形图

最近在研究VAD算法，但调整参数时无法实时看到效果，于是决定将音频波形实时绘制出来，并且语音部分和噪音部分用不同颜色的线条显示，这样就能立即看到VAD算法对各种噪音类型的鲁棒性

为了简化问题规模，先研究出怎么在Android下实时绘制随机生成波形的功能，后面再加入语音获取、根据VAD算法的结果用不同颜色线条显示等功能

查了下Canvas类，发现drawLines方法跟drawLine方法都是根据4个浮点数绘制一条直线，前者还需要开辟额外的空间，所以选择了后者，结果绘制速度很慢，在我的小米2s上绘制2s单通道16KHz采样率16bit位宽的音频，耗时达到700ms，无奈尝试前者，其他条件不变的情况下降至20ms（最快1ms）

由此也能推测出，后者开销这么大主要是花在drawLine的函数调用，而不是坐标点的生成。

代码

package com.happen23.games.waveviewer;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import android.util.Log;import android.view.View;import android.view.ViewTreeObserver;import java.util.Random;/** * Created by Administrator on 2016/5/14. */public class VadView extends View {    private static final String TAG = "VadView";    Paint paint;    int audioSampleNum = 2 * 16000;    int widthPixels;    int heightPixels;    float points[];    short audio[];    public VadView(Context context, AttributeSet attrs) {        super(context, attrs);        paint = new Paint();        paint.setColor(Color.BLUE);        paint.setStrokeJoin(Paint.Join.ROUND);        paint.setStrokeCap(Paint.Cap.ROUND);        paint.setStrokeWidth(1);        getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {            @Override            public void onGlobalLayout() {                widthPixels = getWidth();                heightPixels = getHeight();            }        });    }    protected void drawWave2(Canvas canvas, short audio[]) {        for (int i = 0; i < audioSampleNum-1; i++){            points[4*i] = (float)i/audioSampleNum * widthPixels;            points[4*i+1] = heightPixels/2 + (float)audio[i]/32768 * heightPixels/2;            points[4*i+2] = (float)(i+1)/audioSampleNum * widthPixels;            points[4*i+3] = heightPixels/2 + (float)audio[i+1]/32768 * heightPixels/2;        };        canvas.drawLines(points, paint);    }    protected void drawWave1(Canvas canvas, short audio[]){        float startX, startY, stopX, stopY;        for (int i = 0; i < audio.length-1; i++){            startX = (float)i/audioSampleNum * widthPixels;            startY = heightPixels/2 + (float)audio[i]/32768 * heightPixels/2;            stopX = (float)(i+1)/audioSampleNum * widthPixels;            stopY = heightPixels/2 + (float)audio[i+1]/32768 * heightPixels/2;            canvas.drawLine(startX, startY, stopX, stopY, paint);        }    }    protected void onDraw(Canvas canvas) {        if (points == null) {            points = new float[audioSampleNum * 4];            audio = new short[audioSampleNum];        }        Random r = new Random();        for (int i = 0; i < audioSampleNum; i++){            audio[i] = (short)(r.nextInt(65536) - 32768);        }        Log.w(TAG, "start drawLine");        drawWave2(canvas, audio);        Log.w(TAG, "stop drawLine");        postDelayed(new Runnable() {            @Override            public void run() {                invalidate();            }        }, 200);    }}

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