[PATCH] cam: Convert RGB variations to BGR

[Pavel Machek]

Hi!

> > > > swIsp with libcamera produces ARGB data by default, which needs
> > > > conversion during write. Implement it and similar conversions.
> > > >     
> > > > Signed-off-by: Pavel Machek <pavel at ucw.cz>

> > > > -	const char *row = reinterpret_cast<const char *>(data.data());
> > > > -	for (unsigned int y = 0; y < config.size.height; y++, row += config.stride) {
> > > > -		output.write(row, rowLength);
> > > > +	// Output without any conversion will be slightly faster
> > > 
> > > We use C-style coments.
> > 
> > Can you adjust that while applying?
> 
> If that's the only change required, yes.

Thanks!

> > > > +	const unsigned int inputRowBytes = config.stride; // should be >= width * 4
> > > > +	// Create a temporary buffer to hold one output row.
> > > > +	std::vector<char> rowBuffer(rowLength);
> > > > +	const uint8_t *row = reinterpret_cast<const uint8_t *>(data.data());
> > > > +	for (unsigned int y = 0; y < config.size.height; y++, row += inputRowBytes) {
> > > > +		for (unsigned int x = 0; x < config.size.width; x++) {
> > > > +			const uint8_t *pixel = row + x * bpp;
> > > > +			rowBuffer[x * 3 + 0] = static_cast<char>(pixel[r_pos]);
> > > > +			rowBuffer[x * 3 + 1] = static_cast<char>(pixel[g_pos]);
> > > > +			rowBuffer[x * 3 + 2] = static_cast<char>(pixel[b_pos]);
> > > > +		}
> > > 
> > > I'm curious, what's the performance impact of the conversion ?
> > 
> > I hacked Librem 5 a lot to get libcamera working, and previous config
> > was not working at all, so ... I can't easily benchmark that.
> > 
> > So, this one is not free as it does one more copy of image
> > data. Compared to swIsp, it is going to be lost in the noise.
> > 
> > There's easy optimalization in the original case not to do writes per
> > row if width == stride. There are other options, but they will
> > complicate the code.
> 
> I wonder if it would make sense for the soft ISP to support other RGB
> formats. CC'ing Milan and Hans to get their opinion.

From looking at the code, soft ISP seemed to be able to do other stuff
than ARGB, but for some reason ARGB is selected by default, and I
guess I can get better performance by forcing right format.

Conversion will still be useful for when hardware produces some other
permutation than BGR.

Best regards,
								Pavel
-- 
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