Some Questions & Answers

A few days have gone by since the project was presented, and while I am not very active on the forums and other places where the project have been discussed, I have seen some questions and received some directed ones that I think should be replied to in public view.

1. If I would build and install Arcan, what can I do with it?
To just try things out and play with it, you can for starters build it with SDL as the video platform and run it from X or OSX. It won’t be as fast or have as many features as a more native one like egl-dri, but enough to try it out and play around. A few brave souls have started packaging so that will also help soon. The main application you want to try with it is probably the desktop environment, durden. With it, you have access to the terminal emulator, libretro- cores for games, video player and a vnc client. There is a work-in-progress QEmu integration git and soon a SDL-2 backend. If you are adventurous, it is also possible to build with -DDISABLE_HIJACK=OFF and get a Run with LD_PRELOAD=/path/to/ /my/sdl1.2/program and you should be able to run many (most?) of SDL-1.2 based games and applications.

2. Will this replace
That depends on your needs. For me, it replaced X quite a while ago; I can run my terminal sessions, connect to VNC, run my QEMU virtual machines natively and the emulators I like to play around with all work thanks to libretro. The default video decoder does its job ‘poorly but ok enough’ for my desktop viewing and my multi-monitor setup works better now than it has even done in my 20+ years of trying to stand XFree86/ For others, that’s not enough so that might be reason to wait or simply stay away. It is not like you lack options.

3. How does this all relate to Wayland?
I tried to answer that in the presentation, but it was at the end and perhaps I did not express myself clearly. I intend to support Wayland both as a server and as a client. I’ve had a good look at the protocol (and Quartz, SurfaceFlinger, DWM, for that matter…), and there’s nothing a Wayland implementation needs that isn’t already in place – in terms of features – but the API design and the amount of ‘X’ behaviors Wayland would introduce means that it will an optional thing. There is nothing in Wayland that I have any use for, but there are many things I need in terms of better integration with virtual machine guests and the recent developments in QEmu 2.5/2.6 in regards to dma-buf/render-nodes is highly interesting, so it comes down to priorities or waiting for pull-requests šŸ˜‰

4. Is the Lua scripting necessary?
No, it should take little more effort than removing a compilation unit and about 50 lines of code or so for the scripting interface to disappear in order to run the engine C only – but it is a lot more work telling it what to do and with less support- code for you to re-use. A lot of scripts in Durden, for instance, were written so that you could cut and paste them into other projects. That’s how Senseye will be made usable for people other than myself šŸ™‚

The engine will get a library- build version for such purposes further down the road, but right now there’s no guarantee to the stability of internal interfaces. The same applies to the shared memory interface, even though that already has a library form. I have a few unresolved problems that may require larger changes in these interfaces without considering how any change would affect other people.

5. Will this run faster / better with games?
I have no data to support such a claim, so that’s a maybe. A big point however, is that you can (if you know your Lua, which isn’t very hard) have very good control over what “actually happens” in order to optimize for your needs. For gaming, that would be things like mapping the game output directly to the selected display, without the insanity of the game trying to understand resolution switching and whatever ‘fullscreen’ means. Another possibility would be switching to a simpler set of scripts or mode of operation that suspend and ignores windows that don’t contribute to what you want to do.

6. Is the database- application whitelisting necessary?
No, you can connect to the server using another set of primitives (ARCAN_CONNPATH=…), if the set of scripts you are using allows you to. This is what is meant by “non-authoritative” connection mode and the database can be entirely :memory if you don’t want any settings to be stored. The whitelisting will come into better use later, when you can establish your own “chain of trust”.

7. Is there a way to contribute?Ā 

There are many ways, besides ‘spreading the word’ (and I could use a Vive ;-)). See the wiki page here:

8. The ‘Amiga UI’ is not working?

That’s the reason it was marked as abandoned (and practically since end of 2013). It was just a thing I did to get a feel for how much code it would take to do something like ‘Amiga meets BeOS’ and find out some places where the API had gone wrong. Afterwards, I changed those parts but never updated the related scripts. That said, it is not a big effort to get it up and running again, so maybe…

8. Where does this fit in the Linux/BSD ecosystem?

Where does awk, sed and grep fit? Arcan is a versatile tool that you can use for a lot of kinds of graphics processing and the Desktop case illustrated by Durden is just one. I use a minimal init and boot straight into Durden, using a handful of preset mount and networking settings that render current state and controls into small widgets. No service manager, display manager, boot animation, login manager or message passing IPC.

One of the many problems with interactive graphics in a ‘pipes and filters‘ like ‘user freedomĀ UNIX- way model‘ is that the performance and latency breaks down. You are much more sensitive to those things thanks to the wonders of human cognition. I know some people still think in the ways of ‘a framebuffer with pixels’ but the days of Mode 13Ā are gone. The process now is highly asynchronous and triggered by events far more complicated than a VBLANK interrupt. The design behind Arcan resembles about as close to theĀ ‘pipes and filters’Ā I think I can come without becoming slow or esoteric.

9. Why is there no X support?
This is a big question and ties in with answer 3.Ā  A small part is the cost and pain of implementing such a complete mess, which would mean less time for more interesting things. This is a completely self-financed project, fueled mostly by dissent, cocktails and electronic music, with no strong commercial ambitions — all in the tradition of dumb idealism.

A bigger part in committing to a protocol, or saying ‘I should be compatible with- or replace- project XYZ’ is that you limit yourself to thinking in terms of how those project works and how you should be better than them or outcompete in some way, rather than in terms of ‘how can I do something interesting with this problem in a way that is different from how others have approached it’.

Collectively speaking, we don’t need yet another project or implementation that takes on X and if that already feedsĀ your needs, why change?Ā Some of us, however, need something different.


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