tree bb86d5219450afc8e9206b91c2ed3b07017cdd8b
parent 597082d9d85b183f3c57cc79e40cb8f045f0a99a
author Hannes Winkler <hanneswinkler2000@web.de> 1723144282 +0200
committer GitHub <noreply@github.com> 1723144282 +0000
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Add EGL Surface backing store (#43683)

Allows using an EGL surface as a flutter backing store. Way more convenient for GBM than hacking gbm bo's into GL FBOs.

This resolves https://github.com/flutter/flutter/issues/58363

Currently, the embedder API assumes that the compositor (if it exists) will let flutter render into FBOs or Textures and then composite the whole thing onto the actual (EGL) window surface. I think this assumption is also documented a bit in https://github.com/flutter/flutter/issues/38466

However, in my case, I want let the hardware do the composition (using the linux KMS API), and render each flutter layer into it's own EGL surface.

It's possible to hack around this by creating your own GBM BOs, importing those as EGL images, then importing those as GL Render Buffers and attaching those to GL FBOs and that works (tested it). However, that's basically reimplementing 50% of the whole GBM/EGL "window" system integration for no reason.

This PR adds:
1. To the embedder API:
   - a new kind of OpenGL Backing store: `FlutterOpenGLSurface`
     - consisting of just a `make_current` and destruction callback (plus userdata)
     - the make_current callback should make the target surface current, i.e. `eglMakeCurrent(..., surf, surf)`
     - will be called by the engine before rendering onto the backing store
2. Some wiring to call make_current before rendering into the backing store

## TODO:

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style