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Camera简单使用并通过TextureView预览
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音视频系列的所有总结内容，均可以在本人GitHub找到对应代码实现。

Camera简单使用并通过TextureView预览

一、Camera使用流程：

1.权限：

<uses-permission android:name = "android.permission.CAMERA" />
<uses-feature android:name = "android.hardware.camera" />
<uses-feature android:name = "android.hardware.camera.autofocus" />
//5.0以上注意动态申请

2.打开Camera：

mCamera = Camera.open(mCameraID);

3.预览Camera：

  1. 设置camera接收预览的输出，可以使surfaceTexture或surfaceHolder

    1. mCamera.setPreviewTexture(surfaceTexture);
mCamera.setPreviewDisplay(surfaceHolder);

  2. 设置camera方向，因为camera默认水平。如果固定portrait可以直接旋转90°，但可以先找出屏幕方向再设置

    1. mOrientation = getCameraPreviewOrientation(activity, mCameraID);
mCamera.setDisplayOrientation(mOrientation); 

    2. public static int getCameraPreviewOrientation(Activity activity, int cameraId) {
    if (mCamera == null) {
        throw new RuntimeException("mCamera is null");
    }
    Camera.CameraInfo info = new Camera.CameraInfo();
    Camera.getCameraInfo(cameraId, info);
    int result;
    int degrees = getRotation(activity);
    //前置
    if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
        result = (info.orientation + degrees) % 360;
        result = (360 - result) % 360;
    }
    //后置
    else {
        result = (info.orientation - degrees + 360) % 360;
    }
    return result;
}
          
public static int getRotation(Activity activity) {
    int rotation = activity.getWindowManager().getDefaultDisplay().getRotation();
    int degrees = 0;
    switch (rotation) {
        case Surface.ROTATION_0:
            degrees = 0;
            break;
        case Surface.ROTATION_90:
            degrees = 90;
            break;
        case Surface.ROTATION_180:
            degrees = 180;
            break;
        case Surface.ROTATION_270:
            degrees = 270;
            break;
    }
    return degrees;
}

4.为camera设置预览尺寸：

  1. 问题1：预览图像拉伸变形，camera提供很多个预览尺寸，如何选择最合适的？一种是选择与textureview宽高最接近的；另一种是选择分辨率最大的。第一种效果不好，第二种后置可以，但前置仍有拉伸感。
  2. 问题2：camera.size的width也是大于height，同size进行转化需要注意
  3. 始终注意一点：camera获取的预览尺寸列表都是：宽 > 高，所以在获取选择合适的分辨率时候，都选择把textureview大的边设为宽，小的设为高，再进行选择比较。

5.打开相机，预览的时机：

textureVIew回调中

@Override
    public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
        mPreviewSize = new Size(width, height);
        startPreview();
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int width, int height) {
        focus(width/2, height/2, true); //自动对焦
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
        releasePreview();
        return false;
}

二、手动对焦与自动对焦

1.手动对焦

首先需要给textureView设置一个触摸监听 textureView.setOnTouchListener(this); 传入点击的坐标值。

focus((int) event.getX(), (int) event.getY(), false); 接着需要把坐标值转化为Point。具体代码如下

//focusPoint:点击区域；screenSize屏幕宽高Size对象
QzrCameraManager.getInstance().activeCameraFocus(focusPoint, screenSize, new Camera.AutoFocusCallback() {
            @Override
            public void onAutoFocus(boolean success, Camera camera) {
                isFocusing = false;
                if (!autoFocus) {
                    focusViewWidget.endFocus(success);
                }
            }
        });

接下来在CameraManager中进行处理

    public boolean activeCameraFocus(Point focusPoint, Size screenSize, Camera.AutoFocusCallback focusCallback) {
        if (mCamera == null) {
            Log.e(TAG, "activeCameraFocus: camera is null");
        }
        //点击坐标转化为camera对焦坐标
        Point cameraFocusPoint = CameraUtil.convertToCameraPoint(screenSize, focusPoint);
        Rect cameraFocusRect = CameraUtil.convertToCameraRect(cameraFocusPoint, 100);

        Camera.Parameters parameters = mCamera.getParameters();

        if (Build.VERSION.SDK_INT > 14) {
            if (parameters.getMaxNumFocusAreas() <= 0) {
                //不支持
                return focus(focusCallback);
            }
            clearCameraFocus();
            List<Camera.Area> focusAreas = new ArrayList<>();
            //100是权重
            focusAreas.add(new Camera.Area(cameraFocusRect, 100));
            parameters.setFocusAreas(focusAreas);
            //设置感光区域
            parameters.setMeteringAreas(focusAreas);
            try {
                mCamera.setParameters(parameters);
            } catch (Exception e) {
                Log.e(TAG, "activeCameraFocus: error");
                e.printStackTrace();
                return false;
            }
        }
        return focus(focusCallback);
    }

    private void clearCameraFocus() {
        if (mCamera == null) {
            throw new RuntimeException("mCamera is null");
        }
        mCamera.cancelAutoFocus();
        Camera.Parameters parameters = mCamera.getParameters();
        parameters.setFocusAreas(null);
        parameters.setMeteringAreas(null);
        try {
            mCamera.setParameters(parameters);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private boolean focus(Camera.AutoFocusCallback autoFocusCallback) {
        if (mCamera == null) {
            return false;
        }
        mCamera.cancelAutoFocus();
        mCamera.autoFocus(autoFocusCallback);
        return true;
    }

2.自动对焦

同理手动对焦。只不过需要调用加速度传感器。

focus(textureView.getWidth() / 2, textureView.getHeight() / 2, true);

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