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Re: jpeg image does not show in background

From: Vladimir 'φ-coder/phcoder' Serbinenko
Subject: Re: jpeg image does not show in background
Date: Fri, 01 Oct 2010 22:15:15 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100805 Icedove/3.0.6

On 10/01/2010 08:55 PM, Piscium wrote:
> On 1 October 2010 17:44, BandiPat <address@hidden> wrote:
>> I don't think it's the monitor's resolution that you should be concerned
>> with, but your graphics cards framebuffer.  Since the graphics card's engine
>> hasn't been fully activated yet, you are relegated to the framebuffer only
>> to display images.  Normally this will be 1280x1024 or smaller.
> Well, 1920X1080 displays well with png with a file of 3.2 Mbytes.
>> Have you tried a 1280x1024 size jpeg for your background image?
> Following your suggestion I hacked grub.cfg to display 1280x1024. Then
> I got two other images of this resolution, one png, one jpeg. The png
> displayed well, the jpeg didn't.
> At this point I thought that no jpeg could be displayed. To test this
> hypothesis I started Gimp and created a basic jpeg, with some
> scribbles with a red brush on a white background. The file was
> obviously much smaller than the others I had tested, only 78 Kbytes.
> This file displayed well.
> The conclusion appears to be that the jpeg module in grub2 is very
> fussy about the files that it displays. Note there was nothing special
> about the files I wanted to display. The "green_mountains" was taken
> from a blog, and the two 1280x1024 images were taken from the Gnome
> Art website.
It's not really "nothing particular". With pictures taken by my camera
it works fine.
> There is a file grub-core/video/readers/jpeg.c. It has plenty of debug
> statements like:
>     "grub_error (GRUB_ERR_BAD_FILE_TYPE, "jpeg: huffman decode fails");
> Is there some easy way to read the text of these messages? (I have no
> JTAG and my hardware does not support virtualization).
They aren't debug messages but error messages which are shown if you
call background_image manually.
Bluepill extensions are useless for debugging GRUB and sticking to the
simplest qemu is the best option. Qemu works on any hardware.
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Vladimir 'φ-coder/phcoder' Serbinenko

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