Android Open Source - glassless Waveform View

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License

The source code is released under:

Apache License

Java Source Code

/*
 * Copyright (C) 2013 Google Inc.//from   w ww .  ja va2  s .c  o  m
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.glass.samples.waveform;

import java.util.LinkedList;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.SurfaceView;

/**
 * A view that displays audio data on the screen as a waveform.
 */
public class WaveformView extends SurfaceView {

  // The number of buffer frames to keep around (for a nice fade-out
  // visualization.
  private static final int HISTORY_SIZE = 6;
  
  // To make quieter sounds still show up well on the display, we use
  // +/- 8192 as the amplitude that reaches the top/bottom of the view
  // instead of +/- 32767. Any samples that have magnitude higher than this
  // limit will simply be clipped during drawing.
  private static final float MAX_AMPLITUDE_TO_DRAW = 8192.0f;

  // The queue that will hold historical audio data.
  private LinkedList<short[]> mAudioData;
  private Paint mPaint;

  public WaveformView(Context context) {
    this(context, null, 0);
  }

  public WaveformView(Context context, AttributeSet attrs) {
    this(context, attrs, 0);
  }

  public WaveformView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);

    mAudioData = new LinkedList<short[]>();

    mPaint = new Paint();
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setColor(Color.WHITE);
    mPaint.setStrokeWidth(0);
    mPaint.setAntiAlias(true);
  }

  /**
   * Updates the waveform view with a new "frame" of samples and renders it.
   * The new frame gets added to the front of the rendering queue, pushing the
   * previous frames back, causing them to be faded out visually.
   * 
   * @param buffer the most recent buffer of audio samples.
   */
  public synchronized void updateAudioData(short[] buffer) {
    short[] newBuffer;

    // We want to keep a small amount of history in the view to provide a nice
    // fading effect. We use a linked list that we treat as a queue for this.
    if (mAudioData.size() == HISTORY_SIZE) {
      newBuffer = mAudioData.removeFirst();
      System.arraycopy(buffer, 0, newBuffer, 0, buffer.length);
    } else {
      newBuffer = buffer.clone();
    }

    mAudioData.addLast(newBuffer);

    // Update the display.
    Canvas canvas = getHolder().lockCanvas();
    if (canvas != null) {
      drawWaveform(canvas);
      getHolder().unlockCanvasAndPost(canvas);
    }
  }

  /**
   * Repaints the view's surface.
   * 
   * @param canvas the {@link Canvas} object on which to draw.
   */
  private void drawWaveform(Canvas canvas) {
    // Clear the screen each time because SurfaceView won't do this for us.
    canvas.drawColor(Color.BLACK);

    float width = getWidth();
    float height = getHeight();
    float centerY = height / 2;

    // We draw the history from oldest to newest so that the older audio
    // data is further back and darker than the most recent data.
    int colorDelta = 255 / (HISTORY_SIZE + 1);
    int brightness = colorDelta;

    for (short[] buffer : mAudioData) {
      mPaint.setColor(Color.argb(brightness, 128, 255, 192));

      float lastX = -1;
      float lastY = -1;

      // For efficiency, we don't draw all of the samples in the buffer,
      // but only the ones that align with pixel boundaries.
      for (int x = 0; x < width; x++) {
        int index = (int) ((x / width) * buffer.length);
        short sample = buffer[index];
        float y = (sample / MAX_AMPLITUDE_TO_DRAW) * centerY + centerY;

        if (lastX != -1) {
          canvas.drawLine(lastX, lastY, x, y, mPaint);
        }
        
        lastX = x;
        lastY = y;
      }

      brightness += colorDelta;
    }
  }
}

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