Add `register_native_texture` in `eframe::Frame` (#4246)

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* Closes https://github.com/emilk/egui/issues/4243

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/eframe/src/epi.rs

@@ -614,6 +614,11 @@ pub struct Frame {
     #[cfg(feature = "glow")]
     pub(crate) gl: Option<std::sync::Arc<glow::Context>>,
 
+    /// Used to convert user custom [`glow::Texture`] to [`egui::TextureId`]
+    #[cfg(all(feature = "glow", not(target_arch = "wasm32")))]
+    pub(crate) glow_register_native_texture:
+        Option<Box<dyn FnMut(glow::Texture) -> egui::TextureId>>,
+
     /// Can be used to manage GPU resources for custom rendering with WGPU using [`egui::PaintCallback`]s.
     #[cfg(feature = "wgpu")]
     pub(crate) wgpu_render_state: Option<egui_wgpu::RenderState>,
@@ -690,6 +695,15 @@ impl Frame {
         self.gl.as_ref()
     }
 
+    /// Register your own [`glow::Texture`],
+    /// and then you can use the returned [`egui::TextureId`] to render your texture with [`egui`].
+    ///
+    /// This function will take the ownership of your [`glow::Texture`], so please do not delete your [`glow::Texture`] after registering.
+    #[cfg(all(feature = "glow", not(target_arch = "wasm32")))]
+    pub fn register_native_glow_texture(&mut self, native: glow::Texture) -> egui::TextureId {
+        self.glow_register_native_texture.as_mut().unwrap()(native)
+    }
+
     /// The underlying WGPU render state.
     ///
     /// Only available when compiling with the `wgpu` feature and using [`Renderer::Wgpu`].

crates/eframe/src/native/epi_integration.rs

@@ -152,6 +152,9 @@ impl EpiIntegration {
         native_options: &crate::NativeOptions,
         storage: Option<Box<dyn epi::Storage>>,
         #[cfg(feature = "glow")] gl: Option<std::sync::Arc<glow::Context>>,
+        #[cfg(feature = "glow")] glow_register_native_texture: Option<
+            Box<dyn FnMut(glow::Texture) -> egui::TextureId>,
+        >,
         #[cfg(feature = "wgpu")] wgpu_render_state: Option<egui_wgpu::RenderState>,
     ) -> Self {
         let frame = epi::Frame {
@@ -162,6 +165,8 @@ impl EpiIntegration {
             storage,
             #[cfg(feature = "glow")]
             gl,
+            #[cfg(feature = "glow")]
+            glow_register_native_texture,
             #[cfg(feature = "wgpu")]
             wgpu_render_state,
             raw_display_handle: window.display_handle().map(|h| h.as_raw()),

crates/eframe/src/native/glow_integration.rs

@@ -217,6 +217,7 @@ impl GlowWinitApp {
 
         let system_theme =
             winit_integration::system_theme(&glutin.window(ViewportId::ROOT), &self.native_options);
+        let painter = Rc::new(RefCell::new(painter));
 
         let integration = EpiIntegration::new(
             egui_ctx,
@@ -226,6 +227,10 @@ impl GlowWinitApp {
             &self.native_options,
             storage,
             Some(gl.clone()),
+            Some(Box::new({
+                let painter = painter.clone();
+                move |native| painter.borrow_mut().register_native_texture(native)
+            })),
             #[cfg(feature = "wgpu")]
             None,
         );
@@ -302,7 +307,6 @@ impl GlowWinitApp {
         };
 
         let glutin = Rc::new(RefCell::new(glutin));
-        let painter = Rc::new(RefCell::new(painter));
 
         {
             // Create weak pointers so that we don't keep

crates/eframe/src/native/wgpu_integration.rs

@@ -215,6 +215,8 @@ impl WgpuWinitApp {
             storage,
             #[cfg(feature = "glow")]
             None,
+            #[cfg(feature = "glow")]
+            None,
             wgpu_render_state.clone(),
         );