Why must the glow painter be destroyed manually

[DusterTheFirst]

The following message is printed by tracing after the egui application panics:

WARN egui_glow::painter: You forgot to call destroy() on the egui glow painter. Resources will leak!

Tracking down this message it leads me to the egui_glow painter. In the documentation comment, it notes:

egui/egui_glow/src/painter.rs

Lines 27 to 29 in 465c961

	/// This struct must be destroyed with [`Painter::destroy`] before dropping, to ensure OpenGL
	/// objects have been properly deleted and are not leaked.
	pub struct Painter {

I was wondering what the rationale behind not just using a Drop implementation to clean up the painter resources. There even is a Drop handler that ensures the programmer called this destroy function.

egui/egui_glow/src/painter.rs

Lines 630 to 638 in 465c961

	impl Drop for Painter {
	fn drop(&mut self) {
	if !self.destroyed {
	tracing::warn!(
	"You forgot to call destroy() on the egui glow painter. Resources will leak!"
	);
	}
	}
	}

To me, it would make more sense to call Painter::destroy in the Drop implementation. So that the painter is always cleaned up without the programmer needing to manually call Painter::destroy, and it would destroy the painter in the case of a panic

[emilk]

The problem is that destroy uses the glow::Context, and must be called when the context is still valid, and I think it will be invalidated when the window it is attached to is destroyed. If we called destroy from Drop this could easily happen, and could lead to UB (since all glow functions are unsafe).

[DusterTheFirst]

Would it be possible to check if the context is valid before calling destroy on it?

[CompeyDev]

Right, I'm using a RetainedImage, and I seem to be getting the same warning regarding the glow painter not being destroyed, even though I am not directly using it.

How shall I destroy a glow painter in this case?

[xairaven]

I'm also interested in the solution. @emilk, could you shed some light on this issue?