[U-Boot-Users] [RFC] Splash image

[Jerry Van Baren]

Rodolfo Giometti wrote:
> On Wed, Jul 18, 2007 at 09:40:28AM -0400, Joey Oravec wrote:
>> "Rodolfo Giometti" <giometti at enneenne.com> wrote in message 
>> news:20070718083012.GE4836 at enneenne.com...
>>> I'm planning to review the splash image support and in order to do that
>>> my next steps should be:
>>>
>>> 1) Remove the logo support.
>> As long as it's modular, I agreed because the two functions are nearly 
>> identical. It's important to add/remove code to keep the size down. Probably 
>> should test for a pointer to a compressed (gzip) image, uncompress, then 
>> call the bmp_display.
> 
> I think we should remove it definitely... it's just doubled code.
> 
>>> 2) Rewrite the lcd_display_bitmap() in order to be more portable
>>> across several BPP values.
>> Keep it modular; have a bitmap_display(addr, x, y) robust to bpp that is 
>> called from an lcd_display_splash_screen(). Account for 24-bit LCDs and 
>> files. The bit-per-pixel data structure was a poor-fit with 24-bit, and I 
>> didn't even try to support colormapped files on a truecolor display. Great 
>> idea because it might save a ton of flash to display an 8bpp image on a 
>> 24bpp display.
>>
>> 3. If there's an overall flash savings, it would be nice to support GIF, 
>> PNG, or some other format smaller than a BMP. How complex is the parsing, 
>> and would it be a net savings on flash?
> 
> I think we should support just one format for two reasons:
> 
> 1) Supporting just one format keep the code smallest.
> 
> 2) We have "convert". :)
> 
>> 4. Account for text overlay on splash screen. There are callbacks for bootup 
>> progress, and it's nice to lcd_printf() the status to some rectangle on the 
>> screen. Even better if it scrolls or clears nicely.
>>
>> 5. Document and improve the videolfb ATAG. I hardcode my framebuffer to the 
>> end of RAM, don't tell linux to use that memory, and pass the info to linux. 
>> The display still flickers until you remove the re-initialization, but at 
>> least Linux won't move and therefore clobber the contents of the 
>> framebuffer.
> 
> I dislike this feature. :) IMHO I think it introduces several problems
> and complications whose can be avoided just defining a boot logo into
> Linux... however it could be keep into some consideration.
> 
> Thanks for your suggestions,
> 
> Rodolfo

FWIIW, I took a screenshot, saved it as a 16 bit BMP, then converted the 
BMP as a GIF, JPEG, and a PNG.  While very unscientific, this says BMP 
with gzip is a winner for two reasons:
1) It is similar in compression ratios to PNG and GIF
2) We already know how to gunzip and BMP.

Benchmark:
495410 screenshot-16.bmp

  25411 screenshot-16.bmp.gz
  25875 screenshot-16.PNG
  37727 screenshot-16.GIF
148854 screenshot-16.JPG

(Trivia: I did JPEG because it was there.  It is generally a poor choice 
for splash screens because it has artifacts on sharp transitions, which 
splash screens tend to have.)

gvb