Use X11 display to create EGL display

[wmww]

Description

Use the X11 display to create the EGL display. This brings the implementation in line with the Wayland renderer, and maybe fixes flutter/flutter#60429 (I can't reproduce that, so I do not know for sure). I don't think this raises any thread safety problems, as the display is used with different contexts on each thread.

Related Issues

flutter/flutter#60429

Tests

None

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[robert-ancell]

This used to cause Flutter to crash do to multiple threads accessing xlib. I don't know if there have been changes in Flutter that ensure that can't happen anymore.

[wmww]

I thought we'd be fine because we make our own context and you can use a single EGL display from multiple threads as long as you use multiple contexts. What does the EGL display have to do with xlib? Was it the call to gdk_x11_get_default_xdisplay() itself that was being made on the wrong thread?

[robert-ancell]

I thought we'd be fine because we make our own context and you can use a single EGL display from multiple threads as long as you use multiple contexts. What does the EGL display have to do with xlib? Was it the call to gdk_x11_get_default_xdisplay() itself that was being made on the wrong thread?

EGL is using the Display object from XLib (DRI3 calls?) and GTK is also using the same object for its operations. That's where the collision was occurring.

[robert-ancell]

Based on the EGL X11 extension, perhaps we should be using:

eglGetPlatformDisplayEXT(EGL_PLATFORM_X11_EXT, NULL, NULL);

[wmww]

That looks like it would work, but I can't find what I need to include to get eglGetPlatformDisplayEXT() and EGL_PLATFORM_X11_EXT.

[robert-ancell]

Confirmed the currently proposed code crashes. I ran the demo app created by flutter create, then wildly resized the window to get:

[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
test2: ../../src/xcb_io.c:260: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
Lost connection to device.

[robert-ancell]

Found a solution in #21831