Add api for accessing backend texture via epi (#695)

* Define NativeTexture trait for offscreen rendering
add demo for NativeTexture trait

* write changelog

* add comment for native texture example

* formatting

* add license of Rust logo

* NativeTexture trait method rename
remove duplicate function with native texture
remove rust logo

* deprecated notice for register_glium_texture,register_webgl_texture

* collect deprecated notice

egui_glium/src/lib.rs

@@ -40,7 +40,8 @@ use {
     std::hash::{Hash, Hasher},
 };
 
-pub use copypasta::ClipboardContext; // TODO: remove
+pub use copypasta::ClipboardContext;
+use std::borrow::BorrowMut; // TODO: remove
 
 pub struct GliumInputState {
     pub pointer_pos_in_points: Option<Pos2>,
@@ -644,4 +645,8 @@ impl EguiGlium {
             &self.egui_ctx.texture(),
         );
     }
+
+    pub fn painter_mut(&mut self) -> &mut Painter {
+        self.painter.borrow_mut()
+    }
 }

egui_glium/src/painter.rs

@@ -241,8 +241,7 @@ impl Painter {
         id
     }
 
-    /// register glium texture as egui texture
-    /// Usable for render to image rectangle
+    #[deprecated = "Use: `NativeTexture::register_native_texture` instead"]
     pub fn register_glium_texture(
         &mut self,
         texture: glium::texture::SrgbTexture2d,
@@ -319,3 +318,31 @@ impl Painter {
         }
     }
 }
+
+impl epi::NativeTexture for Painter {
+    type Texture = glium::texture::srgb_texture2d::SrgbTexture2d;
+
+    fn register_native_texture(&mut self, native: Self::Texture) -> egui::TextureId {
+        let id = self.alloc_user_texture();
+        if let egui::TextureId::User(id) = id {
+            if let Some(Some(user_texture)) = self.user_textures.get_mut(id as usize) {
+                *user_texture = UserTexture {
+                    pixels: vec![],
+                    gl_texture: Some(native),
+                }
+            }
+        }
+        id
+    }
+
+    fn replace_native_texture(&mut self, id: egui::TextureId, replacing: Self::Texture) {
+        if let egui::TextureId::User(id) = id {
+            if let Some(Some(user_texture)) = self.user_textures.get_mut(id as usize) {
+                *user_texture = UserTexture {
+                    pixels: vec![],
+                    gl_texture: Some(replacing),
+                };
+            }
+        }
+    }
+}