Improved texture loading (#3315)

* rework loading around `Arc<Loaders>`

* use `Bytes` instead of splitting api

* remove unwraps in `texture_handle`

* make `FileLoader` optional under `file` feature

* hide http load error stack trace from UI

* implement image fit

* support more image sources

* center spinner if we know size ahead of time

* allocate final size for spinner

* improve image format guessing

* remove `ui.image`, `Image`, add `RawImage`

* deprecate `RetainedImage`

* `image2` -> `image`

* add viewer example

* update `examples/image` + remove `svg` and `download_image` exapmles

* fix lints and tests

* fix doc link

* add image controls to `images` example

* add more `From` str-like types

* add api to forget all images

* fix max size

* do not scale original size unless necessary

* fix doc link

* add more docs for `Image` and `RawImage`

* make paint_at `pub`

* update `ImageButton` to use new `Image` API

* fix double rendering

* `SizeHint::Original` -> `Scale` + remove `Option` wrapper

* Update crates/egui/src/load.rs

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

* remove special `None` value for `forget`

* Update crates/egui/src/load.rs

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

* add more examples to `ui.image` + add `include_image` macro

* Update crates/egui/src/ui.rs

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

* update `menu_image_button` to use `ImageSource`

* `OrderedFloat::get` -> `into_inner`

* derive `Eq` on `SizedTexture`

* add `id` to loaders + `is_installed` check

* move `images` to demo + simplify `images` example

* log trace when installing loaders

* fix lint

* fix doc link

* add more documentation

* more `egui_extras::loaders` docs

* Update examples/images/src/main.rs

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

* update `images` example screenshots + readme

* remove unused `rfd` from `images` example

* Update crates/egui_extras/src/loaders/ehttp_loader.rs

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

* add `must_use` on `Image` and `RawImage`

* document `loaders::install` multiple call safety

* Update crates/egui_extras/Cargo.toml

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

* reshuffle `is_loader_installed`

* make `include_image` produce `ImageSource` + update docs

* update `include_image` docs

* remove `None` mentions from loader `forget`

* inline `From` texture id + size for `SizedTexture`

* add warning about statically known path

* change image load error + use in image button

* add `.size()` to `Image`

* Update crates/egui_demo_app/Cargo.toml

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

* add explanations to image viewer ui

---------

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

crates/egui_extras/src/loaders/file_loader.rs

@@ -5,7 +5,13 @@ use egui::{
 };
 use std::{sync::Arc, task::Poll, thread};
 
-type Entry = Poll<Result<Arc<[u8]>, String>>;
+#[derive(Clone)]
+struct File {
+    bytes: Arc<[u8]>,
+    mime: Option<String>,
+}
+
+type Entry = Poll<Result<File, String>>;
 
 #[derive(Default)]
 pub struct FileLoader {
@@ -13,9 +19,17 @@ pub struct FileLoader {
     cache: Arc<Mutex<HashMap<String, Entry>>>,
 }
 
+impl FileLoader {
+    pub const ID: &str = egui::generate_loader_id!(FileLoader);
+}
+
 const PROTOCOL: &str = "file://";
 
 impl BytesLoader for FileLoader {
+    fn id(&self) -> &str {
+        Self::ID
+    }
+
     fn load(&self, ctx: &egui::Context, uri: &str) -> BytesLoadResult {
         // File loader only supports the `file` protocol.
         let Some(path) = uri.strip_prefix(PROTOCOL) else {
@@ -26,9 +40,10 @@ impl BytesLoader for FileLoader {
         if let Some(entry) = cache.get(path).cloned() {
             // `path` has either begun loading, is loaded, or has failed to load.
             match entry {
-                Poll::Ready(Ok(bytes)) => Ok(BytesPoll::Ready {
+                Poll::Ready(Ok(file)) => Ok(BytesPoll::Ready {
                     size: None,
-                    bytes: Bytes::Shared(bytes),
+                    bytes: Bytes::Shared(file.bytes),
+                    mime: file.mime,
                 }),
                 Poll::Ready(Err(err)) => Err(LoadError::Custom(err)),
                 Poll::Pending => Ok(BytesPoll::Pending { size: None }),
@@ -51,7 +66,12 @@ impl BytesLoader for FileLoader {
                     let uri = uri.to_owned();
                     move || {
                         let result = match std::fs::read(&path) {
-                            Ok(bytes) => Ok(bytes.into()),
+                            Ok(bytes) => Ok(File {
+                                bytes: bytes.into(),
+                                mime: mime_guess::from_path(&path)
+                                    .first_raw()
+                                    .map(|v| v.to_owned()),
+                            }),
                             Err(err) => Err(err.to_string()),
                         };
                         let prev = cache.lock().insert(path, Poll::Ready(result));
@@ -70,12 +90,18 @@ impl BytesLoader for FileLoader {
         let _ = self.cache.lock().remove(uri);
     }
 
+    fn forget_all(&self) {
+        self.cache.lock().clear();
+    }
+
     fn byte_size(&self) -> usize {
         self.cache
             .lock()
             .values()
             .map(|entry| match entry {
-                Poll::Ready(Ok(bytes)) => bytes.len(),
+                Poll::Ready(Ok(file)) => {
+                    file.bytes.len() + file.mime.as_ref().map_or(0, |m| m.len())
+                }
                 Poll::Ready(Err(err)) => err.len(),
                 _ => 0,
             })