Kobo wifi PNG display

[AMB-ereader]

I have just got a Kobo wifi (4-bit display version), rooted it and installed the koboWeather[3] app on it.

Something that I haven't seen anywhere in my research is a better way of displaying images other than using the "/usr/local/Kobo/pickel showpic" method. Even the koboWeather app uses this which causes one fairly major drawback - speed. Converting the pygame surface to a raw image takes very many seconds.

By using the ioctl dumper interposer[2] I decoded the relevant ioctl for displaying an image. Then with the aid of one of the libpng example programs[3] I hacked together a program that can read a PNG image and write it to the display without using pickel.

With the aid of this program the koboWeather app's convert_to_raw function requires only a single line to write a PNG file

def convert_to_raw(surface):
    pygame.image.save(surface,"/tmp/img.png");

which can then be displayed with my new program

call(["rpng-kobo", "/tmp/img.png"])

which is much faster than converting to a raw image and displaying it.

My program can also display a PNG image which is not full-screen by passing in the x,y coordinates of the top left of the image like this:

rpng-kobo test.png 300 400

In theory this could be used to make apps more interactive since you don't need to refresh the whole screen for every update - something for further investigation.

I've attached the source code and executable - only tested on an eReader wifi with 4-bit display.

[1] https://bitbucket.org/david_weese/kobo-weather-app
[2] https://github.com/kobolabs/Kobo-Rea...e/master/poser
[3] http://www.libpng.org/pub/png/book/sources.html

[AMB-ereader]

I discovered (after posting) that the code didn't work for all image sizes - specifically odd widths. There was some special case code for odd horizontal pixel positions but that only worked for full size images.

The new version fixes the bug and seems to work for all image sizes (odd and even widths) and positions (odd and even horizontal position). It has only been tested on a Wifi eReader with 4-bit display.

[KevinShort]

Nice work! I'll give it a try on my 8-bit Kobo Wifi when I get some time.

[AMB-ereader]

Originally Posted by KevinShort

Nice work! I'll give it a try on my 8-bit Kobo Wifi when I get some time.

That would be good to know.

If you do try then this newer version might be better. There is still something funny that seems to happen after a suspend/wake cycle (failure to update but restarting nickel fixes it). I added two more ioctl() calls that the pickel program uses and it seemed to make it a bit better.

I have another program that completely blanks the screen but that doesn't help with the task in hand of partial updates. It looks like when a partial update is performed only the pixels that have changed are updated so perhaps it gets confused sometimes about what is already displayed.

[Tandy]

This is excellent! I can confirm it works on my 8-bit version. I'm planning on writing something that looks like Kevin's app, but pulling data from my personal weather station. It will help to be able to render the individual metrics (temp, humidity, wind, etc) individually.

[AMB-ereader]

Originally Posted by Tandy

This is excellent! I can confirm it works on my 8-bit version. I'm planning on writing something that looks like Kevin's app, but pulling data from my personal weather station. It will help to be able to render the individual metrics (temp, humidity, wind, etc) individually.

That's great news.

Did you see my other thread https://www.mobileread.com/forums/sho...d.php?t=235006 where I provided an RSS reader application that made use of this and also included native Python code that could write to the screen directly? This would allow a partial screen update in real-time if you wanted that.

[Kobold001]

I want to test this program, too. The program returns the error /lib/libpng12.so.0: version 'PNG12_0' not found. It looks as I have a newer libpng12.so.0 on my Kobo Glo. Please help me to re-compile the rpng-kobo program.

[frostschutz]

@Kobold001:

I didn't know about this program, my own alternative is here:

https://github.com/frostschutz/Kobo/...show/pngshow.c

You can find it as a binary in my screensaver/autoshelf and some other mods.

Unlike this one it does not support coordinate offsets (yet?) although you can achieve a similar effect using transparency...

[Kobold001]

Thanks frostschutz. I found out that those pngshow programs require a greyscale PNG file with 16 colors. Well, the input PNG files I have, have more colors.

I want to download PNG files from the internet with wget and then display them. This will not work with pngshow without an automatic conversion on the Kobo. I didn't find any converter. That's a pity.

[NiLuJe]

ImageMagick to the rescue!

There's a binary in there, as well as my usual one-liner.

[frostschutz]

Originally Posted by Kobold001

I want to download PNG files from the internet with wget and then display them.

Color depth should not be an issue (my pngshow should support all PNG, if you find one that does not work, send me a copy). The framebuffer of the Kobo is actually full color anyway (RGB565) so if you take a screenshot in the webbrowser you'll see colors too. The conversion to 16 levels grey is something that happens in the e-Ink driver - I guess.

However pngshow is really just a stupid program that draws PNG on screen, it does not do any scaling or whatever, so this should be the main problem when just downloading random images from somewhere.