OpenCV Android解决相机旋转90度及全屏问题

一、图像全屏问题

首先找到CameraBridgeViewBase文件的 protected void deliverAndDrawFrame(CvCameraViewFrame frame)方法，阅读源码发现该方法主要实现的就是相机预览图的绘制，核心代码如下：

if (bmpValid && mCacheBitmap != null) {
    Canvas canvas = getHolder().lockCanvas();
    if (canvas != null) {
        canvas.drawColor(0, android.graphics.PorterDuff.Mode.CLEAR);

        if (mScale != 0) {
            canvas.drawBitmap(mCacheBitmap, new Rect(0, 0, mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
                    new Rect((int) ((canvas.getWidth() - mScale * mCacheBitmap.getWidth()) / 2),
                            (int) ((canvas.getHeight() - mScale * mCacheBitmap.getHeight()) / 2),
                            (int) ((canvas.getWidth() - mScale * mCacheBitmap.getWidth()) / 2 + mScale * mCacheBitmap.getWidth()),
                            (int) ((canvas.getHeight() - mScale * mCacheBitmap.getHeight()) / 2 + mScale * mCacheBitmap.getHeight())), null);
        } else {
            canvas.drawBitmap(mCacheBitmap, new Rect(0, 0, mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
                    new Rect((canvas.getWidth() - mCacheBitmap.getWidth()) / 2,
                            (canvas.getHeight() - mCacheBitmap.getHeight()) / 2,
                            (canvas.getWidth() - mCacheBitmap.getWidth()) / 2 + mCacheBitmap.getWidth(),
                            (canvas.getHeight() - mCacheBitmap.getHeight()) / 2 + mCacheBitmap.getHeight()), null);
        }

        if (mFpsMeter != null) {
            mFpsMeter.measure();
            mFpsMeter.draw(canvas, 20, 30);
        }
        getHolder().unlockCanvasAndPost(canvas);
    }
}

因此将绘制代码重新设计后可以解决图像旋转及全屏问题，解决如下：

if (bmpValid && mCacheBitmap != null) {
    Canvas canvas = getHolder().lockCanvas();
    if (canvas != null) {
        canvas.drawColor(0, android.graphics.PorterDuff.Mode.CLEAR);

		// 修改预览旋转90度问题
		canvas.rotate(90, 0, 0);
		float scale = canvas.getWidth() / (float) mCacheBitmap.getHeight();
		float scale2 = canvas.getHeight() / (float) mCacheBitmap.getWidth();
		if (scale2 > scale) {
		    scale = scale2;
		}
		if (scale != 0) {
		    canvas.scale(scale, scale, 0, 0);
		}
		canvas.drawBitmap(mCacheBitmap, 0, -mCacheBitmap.getHeight(), null);
		// 修改预览旋转90度问题end

        if (mFpsMeter != null) {
            mFpsMeter.measure();
            mFpsMeter.draw(canvas, 20, 30);
        }
        getHolder().unlockCanvasAndPost(canvas);
    }
}

亲测这个方案可行，但是仅仅适用于竖屏并且是后置摄像头，如果改为前置摄像头、横屏模式则不行，还需要进一步修改，考虑到能不修改源码尽量不修改的原则，继续深挖代码。我们尝试在mScale上做文章，JavaCameraView类中有这么一段代码：

if ((getLayoutParams().width == LayoutParams.MATCH_PARENT) && (getLayoutParams().height == LayoutParams.MATCH_PARENT))
    mScale = Math.min(((float)height)/mFrameHeight, ((float)width)/mFrameWidth);
else
    mScale = 0;

这里决定了相机获取图像映射到画布上的缩放比例，很明显取最小值是要保证图像缩放，全部显示在画布上。
修改为裁剪图像，只显示其中间部分，如下：

if ((getLayoutParams().width == LayoutParams.MATCH_PARENT) && (getLayoutParams().height == LayoutParams.MATCH_PARENT)) {
    if (isShowFullPreview()) {
        mScale = Math.min(((float) height) / mFrameHeight, ((float) width) / mFrameWidth);
    } else {
        mScale = Math.max(((float) height) / mFrameHeight, ((float) width) / mFrameWidth);
    }
} else {
    mScale = 0;
}

还有其他解决方案，有兴趣的童鞋可以继续深挖。比如mFpsMeter对象的处理

二、图像旋转问题

旋转问题分为横屏、竖屏分开处理，
1、AndroidManifest.xml文件中指定Activity的屏幕方向：android:screenOrientation。
2、Activity继承CvCameraViewListener2接口，实现public Mat onCameraFrame(CvCameraViewFrame inputFrame)方法。如下：

    @Override
    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        Mat frame = inputFrame.rgba();

        if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT) {

            if (mOpenCvCameraView.isFrontCamare()) {
                Core.rotate(frame, frame, Core.ROTATE_90_COUNTERCLOCKWISE);
                Core.flip(frame, frame, 1);
            } else {
                Core.rotate(frame, frame, Core.ROTATE_90_CLOCKWISE);
            }

        }
        else {
            if (mOpenCvCameraView.isFrontCamare()) {
                Core.flip(frame, frame, 1);
            }
        }

        return frame;
    }

本文地址：https://blog.csdn.net/liuhongshuo2012/article/details/107100870