上一篇文章主要是掌握ZXing解码整体的步骤，关于细节方面的代码就一笔带过了，本篇文章将会深入细节，更详细的讲解有关相机配置方面的知识。
ZXing的相机初始配置
直接看代码，找到调用相机初始化配置的代码，上篇文章已经分析了在CaptureActivity中怎么调到initCamera方法的，这里再次看下这个方法的代码，如下
private void initCamera(SurfaceHolder surfaceHolder) { if (surfaceHolder == null) { throw new IllegalStateException("No SurfaceHolder provided"); } //相机已经打开 if (cameraManager.isOpen()) { Log.w(TAG, "initCamera() while already open -- late SurfaceView callback?"); return; } try { //打开相机并初始化硬件参数 cameraManager.openDriver(surfaceHolder); // 实例化一个handler并开始预览. if (handler == null) { handler = new CaptureActivityHandler(this, decodeFormats, decodeHints, characterSet, cameraManager); } decodeOrStoreSavedBitmap(null, null); } catch (IOException ioe) { Log.w(TAG, ioe); displayFrameworkBugMessageAndExit(); } catch (RuntimeException e) { // Barcode Scanner has seen crashes in the wild of this variety: // java.?lang.?RuntimeException: Fail to connect to camera service Log.w(TAG, "Unexpected error initializing camera", e); displayFrameworkBugMessageAndExit(); } }
上篇文章分析到这句代码
cameraManager.openDriver(surfaceHolder);
就直接说了这句代码的作用，并没有进入openDriver方法详细的看代码，这里看下openDriver中的代码，如下
public synchronized void openDriver(SurfaceHolder holder) throws IOException { OpenCamera theCamera = camera; if (theCamera == null) { //更具requestedCameraId打开对应的摄像头 theCamera = OpenCameraInterface.open(requestedCameraId); if (theCamera == null) { throw new IOException("Camera.open() failed to return object from driver"); } camera = theCamera; } //是否已经初始化，没有初始化则进行初始化 if (!initialized) { initialized = true; configManager.initFromCameraParameters(theCamera);//分析一 if (requestedFramingRectWidth > 0 && requestedFramingRectHeight > 0) { setManualFramingRect(requestedFramingRectWidth, requestedFramingRectHeight); requestedFramingRectWidth = 0; requestedFramingRectHeight = 0; } } Camera cameraObject = theCamera.getCamera(); Camera.Parameters parameters = cameraObject.getParameters(); String parametersFlattened = parameters == null ? null : parameters.flatten(); // Save these, temporarily try { configManager.setDesiredCameraParameters(theCamera, false); } catch (RuntimeException re) { // Driver failed Log.w(TAG, "Camera rejected parameters. Setting only minimal safe-mode parameters"); Log.i(TAG, "Resetting to saved camera params: " + parametersFlattened); // Reset: if (parametersFlattened != null) { parameters = cameraObject.getParameters(); parameters.unflatten(parametersFlattened); try { cameraObject.setParameters(parameters); configManager.setDesiredCameraParameters(theCamera, true); } catch (RuntimeException re2) { // Well, darn. Give up Log.w(TAG, "Camera rejected even safe-mode parameters! No configuration"); } } } cameraObject.setPreviewDisplay(holder); }
这里重点看下“分析一”
initFromCameraParameters
方法中的代码，如下
void initFromCameraParameters(OpenCamera camera) { Camera.Parameters parameters = camera.getCamera().getParameters(); WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); //获取WindowManager默认的Display Display display = manager.getDefaultDisplay(); //屏幕的旋转角度 int displayRotation = display.getRotation(); int cwRotationFromNaturalToDisplay; switch (displayRotation) { case Surface.ROTATION_0: cwRotationFromNaturalToDisplay = 0; break; case Surface.ROTATION_90: cwRotationFromNaturalToDisplay = 90; break; case Surface.ROTATION_180: cwRotationFromNaturalToDisplay = 180; break; case Surface.ROTATION_270: cwRotationFromNaturalToDisplay = 270; break; default: // Have seen this return incorrect values like -90 if (displayRotation % 90 == 0) { cwRotationFromNaturalToDisplay = (360 + displayRotation) % 360; } else { throw new IllegalArgumentException("Bad rotation: " + displayRotation); } } Log.i(TAG, "Display at: " + cwRotationFromNaturalToDisplay); int cwRotationFromNaturalToCamera = camera.getOrientation(); Log.i(TAG, "Camera at: " + cwRotationFromNaturalToCamera); // Still not 100% sure about this. But acts like we need to flip this: if (camera.getFacing() == CameraFacing.FRONT) { cwRotationFromNaturalToCamera = (360 - cwRotationFromNaturalToCamera) % 360; Log.i(TAG, "Front camera overriden to: " + cwRotationFromNaturalToCamera); } /* SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context); String overrideRotationString; if (camera.getFacing() == CameraFacing.FRONT) { overrideRotationString = prefs.getString(PreferencesActivity.KEY_FORCE_CAMERA_ORIENTATION_FRONT, null); } else { overrideRotationString = prefs.getString(PreferencesActivity.KEY_FORCE_CAMERA_ORIENTATION, null); } if (overrideRotationString != null && !"-".equals(overrideRotationString)) { Log.i(TAG, "Overriding camera manually to " + overrideRotationString); cwRotationFromNaturalToCamera = Integer.parseInt(overrideRotationString); } */ cwRotationFromDisplayToCamera = (360 + cwRotationFromNaturalToCamera - cwRotationFromNaturalToDisplay) % 360; Log.i(TAG, "Final display orientation: " + cwRotationFromDisplayToCamera); if (camera.getFacing() == CameraFacing.FRONT) { Log.i(TAG, "Compensating rotation for front camera"); cwNeededRotation = (360 - cwRotationFromDisplayToCamera) % 360; } else { cwNeededRotation = cwRotationFromDisplayToCamera; } Log.i(TAG, "Clockwise rotation from display to camera: " + cwNeededRotation); Point theScreenResolution = new Point(); display.getSize(theScreenResolution); screenResolution = theScreenResolution; Log.i(TAG, "Screen resolution in current orientation: " + screenResolution); cameraResolution = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution); Log.i(TAG, "Camera resolution: " + cameraResolution); bestPreviewSize = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution); Log.i(TAG, "Best available preview size: " + bestPreviewSize); boolean isScreenPortrait = screenResolution.x < screenResolution.y; boolean isPreviewSizePortrait = bestPreviewSize.x > bestPreviewSize.y; if (isScreenPortrait == isPreviewSizePortrait) { previewSizeOnScreen = bestPreviewSize; } else { previewSizeOnScreen = new Point(bestPreviewSize.y, bestPreviewSize.x); } Log.i(TAG, "Preview size on screen: " + previewSizeOnScreen); }
虽然这个方法代码有点多，但是因为这个方法是用来相机初始配置的，所以，要详细的分析一下，首先看下这部分的代码
Camera.Parameters parameters = camera.getCamera().getParameters(); WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); //获取WindowManager默认的Display Display display = manager.getDefaultDisplay(); //屏幕的旋转角度 int displayRotation = display.getRotation(); int cwRotationFromNaturalToDisplay; switch (displayRotation) { case Surface.ROTATION_0: cwRotationFromNaturalToDisplay = 0; break; case Surface.ROTATION_90: cwRotationFromNaturalToDisplay = 90; break; case Surface.ROTATION_180: cwRotationFromNaturalToDisplay = 180; break; case Surface.ROTATION_270: cwRotationFromNaturalToDisplay = 270; break; default: // Have seen this return incorrect values like -90 if (displayRotation % 90 == 0) { cwRotationFromNaturalToDisplay = (360 + displayRotation) % 360; } else { throw new IllegalArgumentException("Bad rotation: " + displayRotation); } } Log.i(TAG, "Display at: " + cwRotationFromNaturalToDisplay); int cwRotationFromNaturalToCamera = camera.getOrientation(); Log.i(TAG, "Camera at: " + cwRotationFromNaturalToCamera); // Still not 100% sure about this. But acts like we need to flip this: if (camera.getFacing() == CameraFacing.FRONT) { cwRotationFromNaturalToCamera = (360 - cwRotationFromNaturalToCamera) % 360; Log.i(TAG, "Front camera overriden to: " + cwRotationFromNaturalToCamera); } cwRotationFromDisplayToCamera = (360 + cwRotationFromNaturalToCamera - cwRotationFromNaturalToDisplay) % 360; Log.i(TAG, "Final display orientation: " + cwRotationFromDisplayToCamera); if (camera.getFacing() == CameraFacing.FRONT) { Log.i(TAG, "Compensating rotation for front camera"); cwNeededRotation = (360 - cwRotationFromDisplayToCamera) % 360; } else { cwNeededRotation = cwRotationFromDisplayToCamera; }
相信没有相机开发经验的同学，看到这段代码会一脸懵逼，没关系，我们一步步来，在理解这段代码前，需要我们掌握下面的一些概念。
- 屏幕坐标： 在Android系统中，屏幕的左上角是坐标系统的原点（0,0）坐标。原点向右延伸是X轴正方向，原点向下延伸是Y轴正方向。
- 自然方向： 每个设备都有一个自然方向，手机和平板的自然方向不同。手机的自然方向是portrait（竖屏），平板的自然方向是landscape（横屏）。
- 图像传感器（Image Sensor）方向： 手机相机的图像数据都是来自于摄像头硬件的图像传感器，这个传感器在被固定到手机上后有一个默认的取景方向，这个方向如下图所示，坐标原点位于手机横放时的左上角：
- 相机图像的预览方向： Android 系统提供一个 API 来手动设置 Camera 的预览方向，叫 setDisplayOrientation。默认情况下这个值是0，与图像 Sensor 方向一致，所以对于横屏应用来说就不需要更改这个 Camera 预览方向。 但是，如果你的应用是竖屏应用，就必须通过这个 API 将 Camera 的预览方向旋转 90 度，让摄像头预览方向与手机屏幕方向保持一致，这样才会得到正确的预览画面。
- 相机采集照片的方向： 这个与相机的预览方向无关，相机采集照片的方向与Image Sensor 方向一致，如果竖屏拍照后直接保存，这时候保存的照片会是横屏的。
强烈建议大家先看下这篇文章 Android: Camera相机开发详解(上) —— 知识储备，相信看过之后，你就会理解上面的代码了，其实，上面代码的作用就是设置相机采集图片的预览方向，就是无论手机是横屏还是竖屏，你看到的图像都是与手机方向一致的。
