bug#74476: [PATCH] Explore JPEG loading without quantization

[Alan Third <alan@idiocy.org>]

On Sat, Nov 30, 2024 at 07:32:10PM +0100, Manuel Giraud wrote:
> Alan Third <alan@idiocy.org> writes:
> 
> > Probably I could do with finding some larger images as the whole thing
> > completes in under a second even without your patch.
> 
> FYI, I have used images of 4000 by 3000 pixels.
> 
> > I've had a quick dig into lookup_rgb_color and assuming you have a
> > true colour display and there's no gamma calculation going on (I don't
> > know when that happens) it shouldn't be doing a whole lot more.
> > Perhaps it's just the extra over-head of calling a function?
> 
> It seems a bit much for just a function call.  Or maybe it is the
> init_color_table call?  Should it be done for each jpeg_load?

It's 4000x3000 function calls, so it might have an effect...

I think it should be done for each load. And I just noticed you need
to add a free_color_table call after you're done with it.

I get that it's a waste of time allocating the table on a true colour
display because it's never going to be used, but it seems to make no
performance difference here and it is still needed on other display
types.

Purely for testing purposes I tried changing the PUT_PIXEL call to
this:

    PUT_PIXEL (ximg, x, y, x_make_truecolor_pixel (FRAME_DISPLAY_INFO(f), r, g, b));

I think it might have given an improvement, but it was so slight I
can't say for sure. That obviously can't be used outside of testing,
but it lets us rule out the function call, etc.
-- 
Alan Third