Add AppBuilder::asset_loader_from_instance (bevyengine#580)

* Implement add_asset_loader_from_instance

* Add example of different data loaders

Cargo.toml

@@ -90,6 +90,7 @@ bevy_gilrs = { path = "crates/bevy_gilrs", optional = true, version = "0.2.1" }
 rand = "0.7.3"
 serde = { version = "1", features = ["derive"] }
 log = "0.4"
+ron = "0.6"
 
 #wasm
 console_error_panic_hook = "0.1.6"
@@ -172,6 +173,10 @@ path = "examples/asset/hot_asset_reloading.rs"
 name = "asset_loading"
 path = "examples/asset/asset_loading.rs"
 
+[[example]]
+name = "custom_loader"
+path = "examples/asset/custom_asset_loading.rs"
+
 [[example]]
 name = "audio"
 path = "examples/audio/audio.rs"

assets/data/test_data.data1

@@ -0,0 +1,3 @@
+ MyCustomData (
+    num: 42
+)

assets/data/test_data.data2

@@ -0,0 +1,3 @@
+ MySecondCustomData (
+    is_set: true
+)

crates/bevy_asset/src/assets.rs

@@ -119,6 +119,10 @@ pub trait AddAsset {
     where
         TLoader: AssetLoader<TAsset> + FromResources,
         TAsset: Send + Sync + 'static;
+    fn add_asset_loader_from_instance<TAsset, TLoader>(&mut self, instance: TLoader) -> &mut Self
+    where
+        TLoader: AssetLoader<TAsset> + FromResources,
+        TAsset: Send + Sync + 'static;
 }
 
 impl AddAsset for AppBuilder {
@@ -135,7 +139,7 @@ impl AddAsset for AppBuilder {
             .add_event::<AssetEvent<T>>()
     }
 
-    fn add_asset_loader<TAsset, TLoader>(&mut self) -> &mut Self
+    fn add_asset_loader_from_instance<TAsset, TLoader>(&mut self, instance: TLoader) -> &mut Self
     where
         TLoader: AssetLoader<TAsset> + FromResources,
         TAsset: Send + Sync + 'static,
@@ -156,7 +160,7 @@ impl AddAsset for AppBuilder {
                 .resources()
                 .get_mut::<AssetServer>()
                 .expect("AssetServer does not exist. Consider adding it as a resource.");
-            asset_server.add_loader(TLoader::from_resources(self.resources()));
+            asset_server.add_loader(instance);
             let handler = ChannelAssetHandler::new(
                 TLoader::from_resources(self.resources()),
                 asset_channel.sender.clone(),
@@ -165,4 +169,14 @@ impl AddAsset for AppBuilder {
         }
         self
     }
+
+    fn add_asset_loader<TAsset, TLoader>(&mut self) -> &mut Self
+    where
+        TLoader: AssetLoader<TAsset> + FromResources,
+        TAsset: Send + Sync + 'static,
+    {
+        self.add_asset_loader_from_instance::<TAsset, TLoader>(TLoader::from_resources(
+            self.resources(),
+        ))
+    }
 }

examples/asset/custom_asset_loading.rs

@@ -0,0 +1,76 @@
+use bevy::{asset::AssetLoader, prelude::*};
+use ron::de::from_bytes;
+use serde::Deserialize;
+use std::path::Path;
+
+#[derive(Deserialize)]
+pub struct MyCustomData {
+    pub num: i32,
+}
+
+#[derive(Deserialize)]
+pub struct MySecondCustomData {
+    pub is_set: bool,
+}
+
+// create a custom loader for data files
+#[derive(Default)]
+pub struct DataFileLoader {
+    matching_extensions: Vec<&'static str>,
+}
+
+impl DataFileLoader {
+    pub fn from_extensions(matching_extensions: Vec<&'static str>) -> Self {
+        DataFileLoader {
+            matching_extensions,
+        }
+    }
+}
+
+impl<TAsset> AssetLoader<TAsset> for DataFileLoader
+where
+    for<'de> TAsset: Deserialize<'de>,
+{
+    fn from_bytes(&self, _asset_path: &Path, bytes: Vec<u8>) -> Result<TAsset, anyhow::Error> {
+        Ok(from_bytes::<TAsset>(bytes.as_slice())?)
+    }
+
+    fn extensions(&self) -> &[&str] {
+        self.matching_extensions.as_slice()
+    }
+}
+
+/// This example illustrates various ways to load assets
+fn main() {
+    App::build()
+        .add_default_plugins()
+        .add_asset::<MyCustomData>()
+        .add_asset_loader_from_instance::<MyCustomData, DataFileLoader>(
+            DataFileLoader::from_extensions(vec!["data1"]),
+        )
+        .add_asset::<MySecondCustomData>()
+        .add_asset_loader_from_instance::<MySecondCustomData, DataFileLoader>(
+            DataFileLoader::from_extensions(vec!["data2"]),
+        )
+        .add_startup_system(setup.system())
+        .run();
+}
+
+fn setup(
+    asset_server: Res<AssetServer>,
+    mut data1s: ResMut<Assets<MyCustomData>>,
+    mut data2s: ResMut<Assets<MySecondCustomData>>,
+) {
+    let data1_handle = asset_server
+        .load_sync(&mut data1s, "assets/data/test_data.data1")
+        .unwrap();
+    let data2_handle = asset_server
+        .load_sync(&mut data2s, "assets/data/test_data.data2")
+        .unwrap();
+
+    let data1 = data1s.get(&data1_handle).unwrap();
+    println!("Data 1 loaded with value {}", data1.num);
+
+    let data2 = data2s.get(&data2_handle).unwrap();
+    println!("Data 2 loaded with value {}", data2.is_set);
+}