Android camera2实现Manual Focus

实现手动对焦，需要使用Camera2 API中提供的控制手动对焦的参数。以下是实现手动对焦的步骤：

1. 获取CameraDevice对象和CaptureRequest.Builder对象。

2. 创建一个CaptureRequest.Builder对象，设置对焦模式为MANUAL。

mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_OFF);

3. 获取当前支持的焦距范围，并将其设置为手动对焦的范围。

Range<Integer>[] focusRanges = characteristics.get(CameraCharacteristics.CONTROL_AF_AVAILABLE_FOCAL_LENGTHS);
mMinFocusDistance = characteristics.get(CameraCharacteristics.LENS_INFO_MINIMUM_FOCUS_DISTANCE);
mMaxFocusDistance = focusRanges[focusRanges.length - 1];

4. 在触摸屏幕时，计算触摸点的相对坐标，并将其转换为相机坐标系中的坐标。

float x = event.getX();
float y = event.getY();
Rect rect = characteristics.get(CameraCharacteristics.SENSOR_INFO_ACTIVE_ARRAY_SIZE);

// 计算触摸点的相对坐标
float relX = x / (float) mTextureView.getWidth();
float relY = y / (float) mTextureView.getHeight();

// 将相对坐标转换为相机坐标系中的坐标
int sensorX = (int) (relX * (float) rect.width());
int sensorY = (int) (relY * (float) rect.height());

5. 计算焦距值，并将其设置为手动对焦的距离。

// 计算焦距值
float focusDistance = calculateFocusDistance(sensorX, sensorY);

// 将焦距值设置为手动对焦的距离
mPreviewRequestBuilder.set(CaptureRequest.LENS_FOCUS_DISTANCE, focusDistance);

6. 发送设置好的请求，启动预览。

mCaptureSession.setRepeatingRequest(mPreviewRequestBuilder.build(), mCaptureCallback, mBackgroundHandler);

7. 计算焦距值的方法：

private float calculateFocusDistance(int sensorX, int sensorY) {
    float hyperFocalDistance = getHyperFocalDistance();
    float d = hyperFocalDistance * (sensorX * mSensorSize.getWidth() / (float) mTextureView.getWidth() - mSensorSize.getWidth() / 2) / (mSensorSize.getWidth() / 2);
    float focusDistance = (hyperFocalDistance * (mMaxFocusDistance - mMinFocusDistance)) / (hyperFocalDistance + d - mMinFocusDistance);
    return focusDistance;
}

private float getHyperFocalDistance() {
    float f = characteristics.get(CameraCharacteristics.LENS_INFO_AVAILABLE_FOCAL_LENGTHS)[0];
    float s = characteristics.get(CameraCharacteristics.LENS_INFO_MINIMUM_FOCUS_DISTANCE);
    float n = characteristics.get(CameraCharacteristics.LENS_INFO_AVAILABLE_APERTURES)[0];
    return (f * f) / (n * s * 2.0f);
}

以上是实现手动对焦的主要步骤。需要注意的是，由于手动对焦需要计算焦距值，因此需要在计算焦距值时，考虑到相机的焦距、最小对焦距离和光圈大小等因素。