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libcamera: v4l2_videodevice: Document plane handling in createBuffer()

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The V4L2VideoDevice::createBuffer() calculates offsets manually when
using a multi-planar pixel format and a single-planar V4L2 format. The
process isn't trivial, document it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Laurent Pinchart 2021-09-03 11:52:20 +03:00
parent 6d98fe5b68
commit 17b9db376c
1 changed files with 9 additions and 0 deletions
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9
src/libcamera/v4l2_videodevice.cpp
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@ -1334,10 +1334,19 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
}
/*
* If we have a multi-planar format with a V4L2 single-planar buffer,
* split the single V4L2 plane into multiple FrameBuffer planes by
* computing the offsets manually.
*
* The format info is not guaranteed to be valid, as there are no
* PixelFormatInfo for metadata formats, so check it first.
*/
if (formatInfo_->isValid() && formatInfo_->numPlanes() != numPlanes) {
/*
* There's no valid situation where the number of colour planes
* differs from the number of V4L2 planes and the V4L2 buffer
* has more than one plane.
*/
ASSERT(numPlanes == 1u);
planes.resize(formatInfo_->numPlanes());