Hi Hans,
Am Montag, den 25.08.2014, 13:38 +0200 schrieb Hans Verkuil:
> Hi Philipp,
>
> I have to think a bit more about the format names, but in the meantime I have
> two other suggestions:
Thank you, I haven't spent much thought about the actual descriptions
yet. Most are just transcribed from the comments in videodev2.h without
looking at the names used in the drivers.
[...]
> > +/**
> > + * struct v4l2_pixfmt - internal V4L2 pixel format description
> > + * @name: format description to be returned by enum_fmt
> > + * @pixelformat: v4l2 pixel format fourcc
> > + * @bpp_line: bits per pixel, averaged over a line (of the first plane
> > + * for planar formats), used to calculate bytesperline
> > + * Zero for compressed and macroblock tiled formats.
> > + * @bpp_image: bits per pixel, averaged over the whole image. This is used to
> > + * calculate sizeimage for uncompressed formats.
> > + * Zero for compressed formats.
>
> I would add a 'planes' field as well for use with formats that use non-contiguous
> planes.
Good point, I'll add that.
[...]
> > +static inline unsigned int v4l2_bytesperline(const struct v4l2_pixfmt *fmt,
> > + unsigned int width)
> > +{
> > + return width * fmt->bpp_line / 8;
>
> Round up: return (width * fmt->bpp_line + 7) / 8;
Right, I should use DIV_ROUND_UP(width * fmt->bpp_line, 8) here.
> > +}
> > +
> > +static inline unsigned int v4l2_sizeimage(const struct v4l2_pixfmt *fmt,
> > + unsigned int width,
> > + unsigned int height)
> > +{
> > + return width * height * fmt->bpp_image / 8;
>
> Ditto: return height * v4l2_bytesperline(fmt, width);
I can't use v4l2_bytesperline because that might be zero for macroblock
tiled formats and uses the wrong bpp value for planar formats with
subsampled chroma.
This nearly works:
return height * DIV_ROUND_UP(width * fmt->bpp_image, 8)
For the planar 4:2:0 subsampled formats and Y41P (bpp_image == 12),
width has to be even, so that is ok.
Most other formats have a bpp_image that is divisible by 8, but there
are the 4:1:0 subsampled formats (bpp_image == 9). Those would round up
width to a multiple of eight, even though it only has to be a multiple
of four. I'd fall back to:
if (fmt->bpp_image == fmt->bpp_line) {
return height * DIV_ROUND_UP(width * fmt->bpp_image, 8);
} else {
/* we know that v4l2_bytesperline doesn't round for planar */
return height * width * fmt->bpp_image / 8;
}
regards
Philipp
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