Patched Xserver that bridge connections to arcan
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README.md

Introduction

This is a patched Xserver with a KDrive backend that uses the arcan-shmif to map Xlib/Xcb/X clients to a running arcan instance.

The initial approach was simply to let the waybridge tool handle X as well, but after some experimentation, the nested translation model proved quite painful to work with, warranting something easier that can be used in the cases where one would not want the overhead of running a full linux-dist inside a QEMU session (the preferred compatibility approach).

Compilation

Normal autohell style compilation. Relevant compilation flags are: --enable-kdrive --enable-xarcan --disable-xorg --disable-xwayland --disable-xnest --disable-xvfb --enable-glamor --enable-glx --disable-int10-module

The only output you are likely to be interested in is hw/kdrive/arcan/Xarcan make install on existing xorg- systems is likely to result in pain as it has its tentacles dug into everything.

pkg_info need to find the normal arcan-shmif, arcan-shmifext libraries.

Though a ton of other X features, could/should also be disabled. If you find a better set of compilation options for a feature- complete yet tiny X server, let me know.

Note that keyboard layouts and fonts are searched on based on the build prefix (like --prefix=/usr), and xfonts2 may need to be built from source on some distributions.

Use

From a terminal with access to connection primitives (env: ARCAN_CONNPATH), just run hw/kdrive/arcan/Xarcan to start bridging connections.

For multiple instances, you can add :1 (and set DISPLAY=:1 etc. accordingly) and so one, forcing size with -screen 800x600 -no-dynamic and enable glamor (GL rendering with handle passing) using -glamor. Note that the ARCAN_RENDER_NODE will be respected (see ISSUES). The title and identity can be scriptably controlled with -aident identstr -atitle titlestr

Clipboard management is not part of xarcan per se, there is an external tool in the arcan source distribution (src/tools/aclip) that can be paired with managers like xclip to bridge clipboard management between arcan instances with appls that support it and the Xserver.

Limitations

The strategy used here is to contain all X clients within one logical window, for mapping single- client windows to corresponding Arcan primitives, the plan is still to go through Wayland/XWayland, though that is still somewhat uncertain, investigations are done on a hybrid version where we can 'steal' single windows out from Xorg on demand. Another exception is if a DRI3 client goes full-screen, then the buffer we passed should switch to that one immediately.

One big limitation is that the keyboard mapping/remapping features that some arcan appls like durden employ will not work here. The server only uses the raw OS keycodes mapped into the sanity absorbing black chasm that is Xkb. Since the same problem exist for bridge wayland clients, chances are that something more dynamic can be obtained via the github.com/39aldo39/klfc util as a middle man.

Issues

There is still some things left to do. Quite a few of the accelerated graphics problems pertain to having multiple GPUs or having Xarcan working against a render node rather than the real device.

This can be mitigated by pointing the ARCAN_RENDER_NODE environment variable to a card-node rather than a render node for starters. This also requires that the xarcan- connection to the running appl- scripts in arcan gets the GPU- delegation flag (durden: global/config/system/gpu delegation=full) as it breaks the privilege separation initiative from using render nodes in the first place.

Notes

(might be wildly incorrect)

There seem to be some weird path/trick needed to be performed for the PRESENT- extension to be enabled, the full path is yet to be traced, but when working, it should be a mere matter of communicating timings and switching to a signal without block- ignore.

The 'Output Segment' todo is a possibly neat way to solve compatibility/mapping for clients that requests the contents of other windows. The plan is to activate when a NEWSEGMENT event arrives with an output segment (i.e. an explicit push).

When that happens, take the pScreen and overload getImage to map/return contents from that segment rather than somewhere else.

TODO

There are still a number of TODOs before all X clients can be successfully bridged, here are the current big points: (x - done, p - partial)

  • Damage- Regions
  • Gamma Control Bridging
  • Randr/DISPLAYHINT resizing
  • Touch Input Mapping
  • Joystick Input Mapping
  • Output Segment to universal GetImage
  • mouse cursor acceleration
  • Display-correct Synchronization timing
    • [p] PRESENT- support
  • [p] Accelerated Cursor
  • Glamor/dri3/glx
  • epoxy patching (or switch gl calls to use agp-fenv)
    • overridable lookup function (map to shmifext-)
    • invalidate / replace
  • xenocara bringup