ZXing源碼解析三：相機的配置與數據的處理
上一篇文章主要是掌握ZXing解碼總體的步驟，關於細節方面的代碼就一筆帶過了，本篇文章將會深刻細節，更詳細的講解有關相機配置方面的知識。java
ZXing的相機初始配置
直接看代碼，找到調用相機初始化配置的代碼，上篇文章已經分析了在CaptureActivity中怎麼調到initCamera方法的，這裏再次看下這個方法的代碼，以下git
private void initCamera(SurfaceHolder surfaceHolder) {
if (surfaceHolder == null) {
throw new IllegalStateException("No SurfaceHolder provided");
}
//相機已經打開
if (cameraManager.isOpen()) {
Log.w(TAG, "initCamera() while already open -- late SurfaceView callback?");
return;
}
try {
//打開相機並初始化硬件參數
cameraManager.openDriver(surfaceHolder);
// 實例化一個handler並開始預覽.
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();
}
}
複製代碼
上篇文章分析到這句代碼cameraManager.openDriver(surfaceHolder);就直接說了這句代碼的做用，並無進入openDriver方法詳細的看代碼，這裏看下openDriver中的代碼，以下github
public synchronized void openDriver(SurfaceHolder holder) throws IOException {
OpenCamera theCamera = camera;
if (theCamera == null) {
//更具requestedCameraId打開對應的攝像頭
theCamera = OpenCameraInterface.open(requestedCameraId);
if (theCamera == null) {
throw new IOException("Camera.open() failed to return object from driver");
}
camera = theCamera;
}
//是否已經初始化，沒有初始化則進行初始化
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);
}
複製代碼
這裏重點看下「分析一」initFromCameraParameters方法中的代碼，以下app
void initFromCameraParameters(OpenCamera camera) {
Camera.Parameters parameters = camera.getCamera().getParameters();
WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
//獲取WindowManager默認的Display
Display display = manager.getDefaultDisplay();
//屏幕的旋轉角度
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);
}
複製代碼
雖然這個方法代碼有點多，可是由於這個方法是用來相機初始配置的，因此，要詳細的分析一下，首先看下這部分的代碼ide
Camera.Parameters parameters = camera.getCamera().getParameters();
WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
//獲取WindowManager默認的Display
Display display = manager.getDefaultDisplay();
//屏幕的旋轉角度
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;
}
複製代碼
相信沒有相機開發經驗的同窗，看到這段代碼會一臉懵逼，不要緊，咱們一步步來，在理解這段代碼前，須要咱們掌握下面的一些概念。post
- 屏幕座標： 在Android系統中，屏幕的左上角是座標系統的原點（0,0）座標。原點向右延伸是X軸正方向，原點向下延伸是Y軸正方向。
- 天然方向： 每一個設備都有一個天然方向，手機和平板的天然方向不一樣。手機的天然方向是portrait（豎屏），平板的天然方向是landscape（橫屏）。
- 圖像傳感器（Image Sensor）方向： 手機相機的圖像數據都是來自於攝像頭硬件的圖像傳感器，這個傳感器在被固定到手機上後有一個默認的取景方向，這個方向以下圖所示，座標原點位於手機橫放時的左上角：
- 相機圖像的預覽方向： Android 系統提供一個 API 來手動設置 Camera 的預覽方向，叫 setDisplayOrientation。默認狀況下這個值是0，與圖像 Sensor 方向一致，因此對於橫屏應用來講就不須要更改這個 Camera 預覽方向。 可是，若是你的應用是豎屏應用，就必須經過這個 API 將 Camera 的預覽方向旋轉 90 度，讓攝像頭預覽方向與手機屏幕方向保持一致，這樣纔會獲得正確的預覽畫面。
- 相機採集照片的方向： 這個與相機的預覽方向無關，相機採集照片的方向與Image Sensor 方向一致，若是豎屏拍照後直接保存，這時候保存的照片會是橫屏的。
強烈建議你們先看下這篇文章 Android: Camera相機開發詳解(上) —— 知識儲備，相信看過以後，你就會理解上面的代碼了，其實，上面代碼的做用就是設置相機採集圖片的預覽方向，就是不管手機是橫屏仍是豎屏，你看到的圖像都是與手機方向一致的。優化
設置相機預覽圖像的最佳比例
文章前部分，已經分析了ZXing設置預覽方向的代碼，可是隻設置預覽方向仍是不夠的，還要根據屏幕的寬高比來找到相機採集圖片最合適的預覽尺寸，不然就會出現相機預覽圖拉伸變形的問題。 繼續看initFromCameraParameters方法中的代碼，以下ui
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);
}
複製代碼
上面代碼中的screenResolution變量是屏幕分辨率，從這個變量中能夠分別獲取屏幕寬高的像素值。咱們來重點看下這兩句代碼this
cameraResolution = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution);
bestPreviewSize = CameraConfigurationUtils.findBestPreviewSizeValue(parameters, screenResolution);
複製代碼
上面的一句代碼是獲取相機的最佳分辨率，下面的一句代碼是獲取獲取相機的最佳預覽尺寸。如今來看下是怎麼獲取最佳尺寸的，findBestPreviewSizeValue方法的代碼以下idea
public static Point findBestPreviewSizeValue(Camera.Parameters parameters, Point screenResolution) {
//獲取相機支持的尺寸，手機不一樣會有不一樣的值
List<Camera.Size> rawSupportedSizes = parameters.getSupportedPreviewSizes();
if (rawSupportedSizes == null) {
Log.w(TAG, "Device returned no supported preview sizes; using default");
Camera.Size defaultSize = parameters.getPreviewSize();
if (defaultSize == null) {
throw new IllegalStateException("Parameters contained no preview size!");
}
return new Point(defaultSize.width, defaultSize.height);
}
if (Log.isLoggable(TAG, Log.INFO)) {
StringBuilder previewSizesString = new StringBuilder();
for (Camera.Size size : rawSupportedSizes) {
previewSizesString.append(size.width).append('x').append(size.height).append(' ');
}
Log.i(TAG, "Supported preview sizes: " + previewSizesString);
}
//這句代碼是獲取屏幕寬高的比例
double screenAspectRatio = screenResolution.x / (double) screenResolution.y;
// Find a suitable size, with max resolution
int maxResolution = 0;
Camera.Size maxResPreviewSize = null;
//for循環的做用是找到相機合適的尺寸和最大的分辨率，這裏
//合適的尺寸指的是和屏幕寬高比相同的尺寸。
for (Camera.Size size : rawSupportedSizes) {
int realWidth = size.width;
int realHeight = size.height;
int resolution = realWidth * realHeight;
if (resolution < MIN_PREVIEW_PIXELS) {
continue;
}
boolean isCandidatePortrait = realWidth < realHeight;
int maybeFlippedWidth = isCandidatePortrait ? realHeight : realWidth;
int maybeFlippedHeight = isCandidatePortrait ? realWidth : realHeight;
double aspectRatio = maybeFlippedWidth / (double) maybeFlippedHeight;
double distortion = Math.abs(aspectRatio - screenAspectRatio);
if (distortion > MAX_ASPECT_DISTORTION) {
continue;
}
//這句代碼是找到與屏幕寬高比一致的尺寸，不然就用相機默認的尺寸
if (maybeFlippedWidth == screenResolution.x && maybeFlippedHeight == screenResolution.y) {
Point exactPoint = new Point(realWidth, realHeight);
Log.i(TAG, "Found preview size exactly matching screen size: " + exactPoint);
return exactPoint;
}
// Resolution is suitable; record the one with max resolution
if (resolution > maxResolution) {
maxResolution = resolution;
maxResPreviewSize = size;
}
}
// If no exact match, use largest preview size. This was not a great idea on older devices because
// of the additional computation needed. We're likely to get here on newer Android 4+ devices, where
// the CPU is much more powerful.
if (maxResPreviewSize != null) {
Point largestSize = new Point(maxResPreviewSize.width, maxResPreviewSize.height);
Log.i(TAG, "Using largest suitable preview size: " + largestSize);
return largestSize;
}
// If there is nothing at all suitable, return current preview size
Camera.Size defaultPreview = parameters.getPreviewSize();
if (defaultPreview == null) {
throw new IllegalStateException("Parameters contained no preview size!");
}
Point defaultSize = new Point(defaultPreview.width, defaultPreview.height);
Log.i(TAG, "No suitable preview sizes, using default: " + defaultSize);
return defaultSize;
}
複製代碼
從上面代碼中的註釋能夠看到這裏存在一些小問題，上面代碼的邏輯是有與屏幕像素比例相同的相機尺寸才返回，不然就用相機默認的尺寸，相機默認的尺寸可能與屏幕的尺寸比有較大的差距，這樣就會出現預覽圖像變形的問題。
這裏能夠將代碼優化爲，返回最接近屏幕寬高比的相機尺寸。這裏的優化將會在後面的文章中進行詳細的講解。
上面的代碼是將一些變量的值設置好，最終，配置相機的參數在CameraConfigurationManager類中的setDesiredCameraParameters中，這裏就不詳細分析了。
旋轉採集圖片的方向
這裏沒有處理採集的照片，採集到的照片數據仍是橫屏的，以下
onPreviewFrame中改變代碼，更改後的代碼以下
@Override
public void onPreviewFrame(byte[] data, Camera camera) {
Point cameraResolution = configManager.getCameraResolution();
Handler thePreviewHandler = previewHandler;
if (cameraResolution != null && thePreviewHandler != null) {
Point screenResolution = configManager.getScreenResolution();
Message message;
if (screenResolution.x < screenResolution.y){
// 手機爲豎屏時
message = thePreviewHandler.obtainMessage(previewMessage, cameraResolution.y,
cameraResolution.x, data);
} else {
// 手機爲橫屏時
message = thePreviewHandler.obtainMessage(previewMessage, cameraResolution.x,
cameraResolution.y, data);
}
message.sendToTarget();
previewHandler = null;
} else {
Log.d(TAG, "Got preview callback, but no handler or resolution available");
}
複製代碼
解釋：手機豎屏時，相機傳感器採集的數據爲橫屏的數據，爲了與豎屏相對應，須要將相機採集的圖片寬高互換，這裏只是互換了寬高，可是採集的數據寬高並無轉換，所以還須要將數據的寬高轉換。
代碼以下
//將原始圖像傳感器的數據轉換爲豎屏
if (width < height) {
// portrait
byte[] rotatedData = new byte[data.length];
for (int x = 0; x < width; x++) {
for (int y = 0; y < height; y++)
rotatedData[y * width + width - x - 1] = data[y + x * height];
}
data = rotatedData;
}
複製代碼
將上面的代碼，加入到DecodeHandler類中的decode方法開頭便可。
雖然，這時已經將相機採集的橫屏數據轉化爲豎屏的了，可是，工做尚未完成，還須要設置獲取二維碼的區域，設置的方法是CameraManager類中的getFramingRectInPrevie方法。這裏我就補貼具體的代碼了，你們根據前文的內容和本身的思考來修改裏面的代碼。
結束語
文章主要分析了相機配置的代碼，選擇拍攝圖像的最佳尺寸及處理相機採集到的數據，重點是要理解相機的數據採集與圖像預覽的設置。本篇修改的代碼在這裏。
本文已由公衆號「AndroidShared」首發
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