设置TextureView（Camera2）全屏预览不拉伸

关于拉伸问题，要使预览不变形，需要使用Matrix：

首先把视频区移动到View区，使两者中心点重合。

matrix.preTranslate((textureViewWidth - viewWidth) / 2, (textureViewHeight - viewHeight) / 2);

其次，因为默认视频是fitXY的形式显示的，所以首先要缩放还原回来。

matrix.preScale(viewWidth/ textureViewWidth, viewHeight/ textureViewHeight);

最后等比例放大或缩小，直到视频区的一边和View一边相等，不相等则留白。

　　　　 int rotation = getWindowManager().getDefaultDisplay().getRotation();
        Matrix matrix = new Matrix();
        RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
        RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
        float centerX = viewRect.centerX();
        float centerY = viewRect.centerY();
        if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
            bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
            matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
            float scale = Math.max(
                    (float) viewHeight / mPreviewSize.getHeight(),
                    (float) viewWidth / mPreviewSize.getWidth());
            matrix.postScale(scale, scale, centerX, centerY);
            matrix.postRotate(90 * (rotation - 2), centerX, centerY);
        } else if (Surface.ROTATION_180 == rotation) {
            matrix.postRotate(180, centerX, centerY);
        }
        mTextureView.setTransform(matrix);

不考虑全屏的情况下设置TextureView大小为可支持的最大size即可：

 Size largest = Collections.max(
                Arrays.asList(mMap.getOutputSizes(ImageFormat.JPEG)),
                new CompareSizesByArea());

要使TextureView全屏，重写TextureView的onMeasure方法：

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        if (0 == mRatioWidth || 0 == mRatioHeight) {
            setMeasuredDimension(width, height);
        } else {
            //设置为大于判断时，textureView全屏预览，小于号时，按比例留白预览
            if (width > height * mRatioWidth / mRatioHeight) {
                setMeasuredDimension(width, width * mRatioHeight / mRatioWidth);
            } else {
                setMeasuredDimension(height * mRatioWidth / mRatioHeight, height);
            }
        }
    }

这段代码使得TextureView在宽高都不超过手机屏幕的情况下最大化显示。
解决方案是，让TextureView总是达到最大边界，超出部分不进行预览，但实际上还是能拍到的