[libcamera-devel] [PATCH v2 12/27] libcamera: v4l2_videodevice: Take stride into account to compute offsets

[Jean-Michel Hautbois]

Hi Laurent,

On 06/09/2021 04:00, Laurent Pinchart wrote:
> When creating FrameBuffer instances, the V4L2VideoDevice computes plane
> offsets using minimal stride for the format. This doesn't always produce
> a valid result when the device requires padding at the end of lines. Fix
> it by computing offsets using the stride reported by V4L2.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index 88535f5a07c7..c6c9263c49e9 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1354,11 +1354,21 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
>  		size_t offset = 0;
>  
>  		for (size_t i = 0; i < planes.size(); ++i) {
> +			/*
> +			 * The stride is reported by V4L2 for the first plane
> +			 * only. Compute the stride of the other planes by
> +			 * taking the horizontal subsampling factor into
> +			 * account, which is equal to the bytesPerGroup ratio of
> +			 * the planes.
> +			 */
> +			unsigned int stride = format_.planes[0].bpl
> +					    * formatInfo_->planes[i].bytesPerGroup
> +					    / formatInfo_->planes[0].bytesPerGroup;
> +
>  			planes[i].fd = fd;
>  			planes[i].offset = offset;
> -
> -			/* \todo Take the V4L2 stride into account */
> -			planes[i].length = formatInfo_->planeSize(format_.size, i);
> +			planes[i].length = formatInfo_->planeSize(format_.size.height,
> +								  i, stride);
>  			offset += planes[i].length;
>  		}
>  	}
>