[Linux] Don't clear the OpenGL context when a frame has been drawn

[robert-ancell]

The draw handler made a context current to draw the frame with, then cleared it, leaving no context current at all while GTK finished the frame.

GTK makes the context it needs current before using OpenGL, so this doesn't need to be cleared. But GTK doesn't check that making its context current succeeded, and if it fails it carries on and uses OpenGL with no context current, which crashes.

Leaving the context current means GTK still has one to fall back on when this happens, so it doesn't crash.

See #191775

[flutter-dashboard]

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[gemini-code-assist]

Code Review

This pull request removes the call to gdk_gl_context_clear_current from the drawing loop in fl_view_renderer_opengl.cc to prevent GTK from crashing due to an unbound context. Feedback highlights that leaving the context bound indefinitely could lead to resource leaks or dangling pointer crashes, and recommends clearing the context during the disposal or destruction phase of the renderer.

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engine/src/flutter/shell/platform/linux/fl_view_renderer_opengl.cc (184-186)

Removing gdk_gl_context_clear_current() from the draw loop means self->render_context will remain bound as the current GL context on the GTK main thread indefinitely.\n\nWhen the renderer or view is destroyed, self->render_context is unreferenced. If it is still the current context on the thread, this can lead to:\n1. Resource Leaks: The GL driver or GDK may keep a reference to the current context, preventing it and its associated resources from being freed.\n2. Dangling Pointer / Crashes: If the context is freed but remains set as current in the thread's thread-local storage, subsequent GL operations or context switches on the main thread may dereference a dangling pointer and crash.\n\nTo prevent this, please ensure that gdk_gl_context_clear_current() is called during the disposal/destruction phase of FlViewRendererOpengl (e.g., in fl_view_renderer_opengl_dispose or fl_view_renderer_opengl_finalize).

[mattkae]

One piece of feedback to consider!

[mattkae]

This feels like a weird, unexpected side effect for a caller potentially. Can this be documented on the method instead, that it will be leftover?

[robert-ancell]

Do you mean the documentation on fl_view_renderer_opengl_draw? This is a callback from GTK, not called by anything else. So the behaviour is specific to GTK and confirmed by inspecting the GTK source.