同步发表于http://avenwu.net/2015/09/15/zxing_view_finder_laser
在很多应用中都有二维码扫描的需求，比如微信，通过扫描电脑二维码，实现用户登录授权；
Google出品的zxing时比较出名的二维码扫描库，但是和其他开源组件不同，zxing包含了很多东西，同时github上的官方实例也较为复杂，如果初次接触，要很快集成扫码并自定UI并不容易；
本文通过分析zxing官方app，揭开扫码镭射线的实现方案；
https://github.com/zxing/zxing
镭射线
如下图，这是zxing实例的默认效果
但是在很多情况下需要根据项目需求自定义，如类似微信的扫描框及扫描线
源码分析
通过分析zxing项目可以知道扫描框对应的时一个自定义的view：ViewfinderView，但就这个类来说，代码量200左右
/*
* Copyright (C) 2008 ZXing authors
*
* 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.zxing.client.android;
import com.google.zxing.ResultPoint;
import com.google.zxing.client.android.camera.CameraManager;
import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;
import java.util.ArrayList;
import java.util.List;
/**
* This view is overlaid on top of the camera preview. It adds the viewfinder rectangle and partial
* transparency outside it, as well as the laser scanner animation and result points.
*
* @author dswitkin@google.com (Daniel Switkin)
*/
public final class ViewfinderView extends View {
private static final int[] SCANNER_ALPHA = {0, 64, 128, 192, 255, 192, 128, 64};
private static final long ANIMATION_DELAY = 80L;
private static final int CURRENT_POINT_OPACITY = 0xA0;
private static final int MAX_RESULT_POINTS = 20;
private static final int POINT_SIZE = 6;
private CameraManager cameraManager;
private final Paint paint;
private Bitmap resultBitmap;
private final int maskColor;
private final int resultColor;
private final int laserColor;
private final int resultPointColor;
private int scannerAlpha;
private List<ResultPoint> possibleResultPoints;
private List<ResultPoint> lastPossibleResultPoints;
// This constructor is used when the class is built from an XML resource.
public ViewfinderView(Context context, AttributeSet attrs) {
super(context, attrs);
// Initialize these once for performance rather than calling them every time in onDraw().
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
Resources resources = getResources();
maskColor = resources.getColor(R.color.viewfinder_mask);
resultColor = resources.getColor(R.color.result_view);
laserColor = resources.getColor(R.color.viewfinder_laser);
resultPointColor = resources.getColor(R.color.possible_result_points);
scannerAlpha = 0;
possibleResultPoints = new ArrayList<>(5);
lastPossibleResultPoints = null;
}
public void setCameraManager(CameraManager cameraManager) {
this.cameraManager = cameraManager;
}
@SuppressLint("DrawAllocation")
@Override
public void onDraw(Canvas canvas) {
if (cameraManager == null) {
return; // not ready yet, early draw before done configuring
}
Rect frame = cameraManager.getFramingRect();
Rect previewFrame = cameraManager.getFramingRectInPreview();
if (frame == null || previewFrame == null) {
return;
}
int width = canvas.getWidth();
int height = canvas.getHeight();
// Draw the exterior (i.e. outside the framing rect) darkened
paint.setColor(resultBitmap != null ? resultColor : maskColor);
canvas.drawRect(0, 0, width, frame.top, paint);
canvas.drawRect(0, frame.top, frame.left, frame.bottom + 1, paint);
canvas.drawRect(frame.right + 1, frame.top, width, frame.bottom + 1, paint);
canvas.drawRect(0, frame.bottom + 1, width, height, paint);
if (resultBitmap != null) {
// Draw the opaque result bitmap over the scanning rectangle
paint.setAlpha(CURRENT_POINT_OPACITY);
canvas.drawBitmap(resultBitmap, null, frame, paint);
} else {
// Draw a red "laser scanner" line through the middle to show decoding is active
paint.setColor(laserColor);
paint.setAlpha(SCANNER_ALPHA[scannerAlpha]);
scannerAlpha = (scannerAlpha + 1) % SCANNER_ALPHA.length;
int middle = frame.height() / 2 + frame.top;
canvas.drawRect(frame.left + 2, middle - 1, frame.right - 1, middle + 2, paint);
float scaleX = frame.width() / (float) previewFrame.width();
float scaleY = frame.height() / (float) previewFrame.height();
List<ResultPoint> currentPossible = possibleResultPoints;
List<ResultPoint> currentLast = lastPossibleResultPoints;
int frameLeft = frame.left;
int frameTop = frame.top;
if (currentPossible.isEmpty()) {
lastPossibleResultPoints = null;
} else {
possibleResultPoints = new ArrayList<>(5);
lastPossibleResultPoints = currentPossible;
paint.setAlpha(CURRENT_POINT_OPACITY);
paint.setColor(resultPointColor);
synchronized (currentPossible) {
for (ResultPoint point : currentPossible) {
canvas.drawCircle(frameLeft + (int) (point.getX() * scaleX),
frameTop + (int) (point.getY() * scaleY),
POINT_SIZE, paint);
}
}
}
if (currentLast != null) {
paint.setAlpha(CURRENT_POINT_OPACITY / 2);
paint.setColor(resultPointColor);
synchronized (currentLast) {
float radius = POINT_SIZE / 2.0f;
for (ResultPoint point : currentLast) {
canvas.drawCircle(frameLeft + (int) (point.getX() * scaleX),
frameTop + (int) (point.getY() * scaleY),
radius, paint);
}
}
}
// Request another update at the animation interval, but only repaint the laser line,
// not the entire viewfinder mask.
postInvalidateDelayed(ANIMATION_DELAY,
frame.left - POINT_SIZE,
frame.top - POINT_SIZE,
frame.right + POINT_SIZE,
frame.bottom + POINT_SIZE);
}
}
public void drawViewfinder() {
Bitmap resultBitmap = this.resultBitmap;
this.resultBitmap = null;
if (resultBitmap != null) {
resultBitmap.recycle();
}
invalidate();
}
/**
* Draw a bitmap with the result points highlighted instead of the live scanning display.
*
* @param barcode An image of the decoded barcode.
*/
public void drawResultBitmap(Bitmap barcode) {
resultBitmap = barcode;
invalidate();
}
public void addPossibleResultPoint(ResultPoint point) {
List<ResultPoint> points = possibleResultPoints;
synchronized (points) {
points.add(point);
int size = points.size();
if (size > MAX_RESULT_POINTS) {
// trim it
points.subList(0, size - MAX_RESULT_POINTS / 2).clear();
}
}
}
}
主要的绘制逻辑都在onDraw()内，这里面包含了扫描框的绘制，识别点的绘制，以及镭射线的绘制，现在我们只需关注其中的镭射线和扫描框部分逻辑
- 首先确定扫描框的位置，计算大小等
//这里简单判断摄像头相关的资源是否准备完毕，只有ok的情况才会继续绘制
if (cameraManager == null) {
return; // not ready yet, early draw before done configuring
}
//获取摄像机画面中用于防止扫描框的区域Rect
Rect frame = cameraManager.getFramingRect();
Rect previewFrame = cameraManager.getFramingRectInPreview();
if (frame == null || previewFrame == null) {
return;
}
int width = canvas.getWidth();
int height = canvas.getHeight();
// Draw the exterior (i.e. outside the framing rect) darkened
paint.setColor(resultBitmap != null ? resultColor : maskColor);
canvas.drawRect(0, 0, width, frame.top, paint);
canvas.drawRect(0, frame.top, frame.left, frame.bottom + 1, paint);
canvas.drawRect(frame.right + 1, frame.top, width, frame.bottom + 1, paint);
canvas.drawRect(0, frame.bottom + 1, width, height, paint);
- 接下来绘制扫描线
// Draw a red "laser scanner" line through the middle to show decoding is active
paint.setColor(laserColor);
paint.setAlpha(SCANNER_ALPHA[scannerAlpha]);
//扫描线的alpha每次都不同，目的是通过刷新画布，实现扫描线闪烁的效果
scannerAlpha = (scannerAlpha + 1) % SCANNER_ALPHA.length;
int middle = frame.height() / 2 + frame.top;
canvas.drawRect(frame.left + 2, middle - 1, frame.right - 1, middle + 2, paint);
- 让扫描线显示并动起来
// Request another update at the animation interval, but only repaint the laser line,
// not the entire viewfinder mask.
postInvalidateDelayed(ANIMATION_DELAY,
frame.left - POINT_SIZE,
frame.top - POINT_SIZE,
frame.right + POINT_SIZE,
frame.bottom + POINT_SIZE);
这里通过局部刷新的方式，每80毫秒重绘一次镭射线；
小结
实际上通过上面的三段代码，我们就已经实现了扫码的一部分即贮备扫描框和镭射线，后续会通过其他文章继续优化我们的扫描框和摄像头的使用；
项目位于：https://github.com/avenwu/zxing-support
本文所对应的代码位于tag-v1：https://github.com/avenwu/zxing-support/releases/tag/tag-v1