Make individual egui_extras image loaders public (#7551)

This was initially a PR to add kitdiff, but this now lives in it's own
crate: https://github.com/rerun-io/kitdiff

I needed to make the image loaders public, this way it's possible to
compose image loaders together (which allowed me to create a image diff
loader that uses two other image loaders). But you can't use the
`ctx.try_load_image` since that would deadlock, so you have to store a
reference to the other loader in the wrapping loader.

crates/egui/src/load.rs

@@ -387,7 +387,7 @@ pub type ImageLoadResult = Result<ImagePoll>;
 /// An `ImageLoader` decodes raw bytes into a [`ColorImage`].
 ///
 /// Implementations are expected to cache at least each `URI`.
-pub trait ImageLoader {
+pub trait ImageLoader: std::any::Any {
     /// Unique ID of this loader.
     ///
     /// To reduce the chance of collisions, include `module_path!()` as part of this ID.
@@ -517,6 +517,16 @@ impl TexturePoll {
             Self::Ready { texture } => Some(texture.id),
         }
     }
+
+    #[inline]
+    pub fn is_pending(&self) -> bool {
+        matches!(self, Self::Pending { .. })
+    }
+
+    #[inline]
+    pub fn is_ready(&self) -> bool {
+        matches!(self, Self::Ready { .. })
+    }
 }
 
 pub type TextureLoadResult = Result<TexturePoll>;

crates/egui_extras/src/lib.rs

@@ -17,7 +17,7 @@ pub mod syntax_highlighting;
 #[doc(hidden)]
 pub mod image;
 mod layout;
-mod loaders;
+pub mod loaders;
 mod sizing;
 mod strip;
 mod table;

crates/egui_extras/src/loaders.rs

@@ -63,9 +63,9 @@ pub fn install_image_loaders(ctx: &egui::Context) {
     }
 
     #[cfg(feature = "http")]
-    if !ctx.is_loader_installed(self::ehttp_loader::EhttpLoader::ID) {
+    if !ctx.is_loader_installed(self::http_loader::EhttpLoader::ID) {
         ctx.add_bytes_loader(std::sync::Arc::new(
-            self::ehttp_loader::EhttpLoader::default(),
+            self::http_loader::EhttpLoader::default(),
         ));
         log::trace!("installed EhttpLoader");
     }
@@ -108,16 +108,16 @@ pub fn install_image_loaders(ctx: &egui::Context) {
 }
 
 #[cfg(not(target_arch = "wasm32"))]
-mod file_loader;
+pub mod file_loader;
 
 #[cfg(feature = "http")]
-mod ehttp_loader;
+pub mod http_loader;
 
 #[cfg(feature = "gif")]
-mod gif_loader;
+pub mod gif_loader;
 #[cfg(feature = "image")]
-mod image_loader;
+pub mod image_loader;
 #[cfg(feature = "svg")]
-mod svg_loader;
+pub mod svg_loader;
 #[cfg(feature = "webp")]
-mod webp_loader;
+pub mod webp_loader;