Looking for framebuffer documentation

[Mr Dini]

Hey,

I recently became a somewhat satisfied owner of a PB Basic Lux 4. Even managed to write some basic GUI apps with C using inkview, but I would love to get fyne (golang GUI framework) to work on this. That would open up many doors and I would be able to write GUI apps in golang.

I took a quick look at libinkview and if I am not mistaken, it doesn't open the framebuffer (fb0) directly, but calls out to libhwconfig.so which opens the device and initializes it.

Is there some docs about the exact commands, what to write, how to initialize whatsoever? I have a very simple use-case. I have a buffer I want to write and I want to display that on the screen directly from golang.

I saw the insane work that was put into https://github.com/NiLuJe/FBInk, but it's not PB specific and quite large... Is there any other resource I could look at? What would you recommend?

I do not have too much experience in this, but I am willing to learn.

Thanks

[Mr Dini]

Actually, I figured out. If anyone else needs something similar, https://github.com/koreader/koreader-base/issues/1202/ is a great read. On the other hand, https://github.com/NiLuJe/FBInk/pull/47/files is a pure gold mine.

Apparently writing to the framebuffer itself is pretty much standard. You first need to obtain VarScreenInfo (0x4600) and FixScreenInfo (0x4602) using ioctl calls and parse the structs. FixScreenInfo has an SmemLen field which you can use to mmap either /dev/fb0 or the userspace library also tries to open /dev/graphics/fb0 if the first one fails. Finally, I can write grayscale pixels to the mapped fb0 based on the width, height (in VarScreenInfo) and lineLength (in FixScreenInfo).

But after doing all that I didn't see a thing. I knew from libinkview that I need to somehow trigger an update. Reverse engineering is really painful, because dynamically mapped functions are called with dynamically extracted values. Thanfully the FBInk implementation figured it out mostly for me. So we need to send MXCFB_SEND_UPDATE ioctl with certain flags. I would love to read more on details such as temp and dithering/waveform modes. For now I just hard-coded the values fbink used too.

Find the final piece of code here: https://gist.github.com/Diniboy1123/...681ae887d10774

Works fine, displays the image on the screen. It's obviously not optimized at all, but I am glad I got it working. Hope it will be helpful to someone.

[orontee]

Originally Posted by Mr Dini

Hey,
I saw the insane work that was put into https://github.com/NiLuJe/FBInk, but it's not PB specific and quite large... Is there any other resource I could look at? What would you recommend?

koreader skip the usual initialization offererd by Inkview API (they don't call InkViewMain() to install an event handler) and if I understand well they writes directly to the framebuffer (no call to DrawImage(), etc.). See (and other files with pocketbook in their name in same directory):

https://github.com/koreader/koreader...pocketbook.lua