Add image sampler configuration in GLTF loader (#17875)

I can't underrate anisotropic filtering.

# Objective

- Allow easily enabling anisotropic filtering on glTF assets.
- Allow selecting `ImageFilterMode` for glTF assets at runtime.

## Solution

- Added a Resource `DefaultGltfImageSampler`: it stores
`Arc<Mutex<ImageSamplerDescriptor>>` and the same `Arc` is stored in
`GltfLoader`. The default is independent from provided to `ImagePlugin`
and is set in the same way but with `GltfPlugin`. It can then be
modified at runtime with `DefaultGltfImageSampler::set`.
- Added two fields to `GltfLoaderSettings`: `default_sampler:
Option<ImageSamplerDescriptor>` to override aforementioned global
default descriptor and `override_sampler: bool` to ignore glTF sampler
data.

## Showcase

Enabling anisotropic filtering as easy as:
```rust
app.add_plugins(DefaultPlugins.set(GltfPlugin{
    default_sampler: ImageSamplerDescriptor {
        min_filter: ImageFilterMode::Linear,
        mag_filter: ImageFilterMode::Linear,
        mipmap_filter: ImageFilterMode::Linear,
        anisotropy_clamp: 16,
        ..default()
    },
    ..default()
}))
```

Use code below to ignore both the global default sampler and glTF data,
having `your_shiny_sampler` used directly for all textures instead:
```rust
commands.spawn(SceneRoot(asset_server.load_with_settings(
    GltfAssetLabel::Scene(0).from_asset("models/test-scene.gltf"),
    |settings: &mut GltfLoaderSettings| {
        settings.default_sampler = Some(your_shiny_sampler);
        settings.override_sampler = true;
    }
)));
```
Remove either setting to get different result! They don't come in pair!

Scene rendered with trillinear texture filtering:

![Trillinear](https://github.com/user-attachments/assets/be4c417f-910c-4806-9e64-fd2c21b9fd8d)
Scene rendered with 16x anisotropic texture filtering:
![Anisotropic Filtering
x16](https://github.com/user-attachments/assets/68190be8-aabd-4bef-8e97-d1b5124cce60)

## Migration Guide

- The new fields in `GltfLoaderSettings` have their default values
replicate previous behavior.

---------

Co-authored-by: Greeble <166992735+greeble-dev@users.noreply.github.com>

Author: axlitEels

crates/bevy_gltf/src/lib.rs

@@ -97,11 +97,15 @@ mod vertex_attributes;
 
 extern crate alloc;
 
+use alloc::sync::Arc;
+use std::sync::Mutex;
+
 use bevy_platform::collections::HashMap;
 
 use bevy_app::prelude::*;
 use bevy_asset::AssetApp;
-use bevy_image::CompressedImageFormats;
+use bevy_ecs::prelude::Resource;
+use bevy_image::{CompressedImageFormats, ImageSamplerDescriptor};
 use bevy_mesh::MeshVertexAttribute;
 use bevy_render::renderer::RenderDevice;
 
@@ -115,10 +119,57 @@ pub mod prelude {
 
 pub use {assets::*, label::GltfAssetLabel, loader::*};
 
+// Has to store an Arc<Mutex<...>> as there is no other way to mutate fields of asset loaders.
+/// Stores default [`ImageSamplerDescriptor`] in main world.
+#[derive(Resource)]
+pub struct DefaultGltfImageSampler(Arc<Mutex<ImageSamplerDescriptor>>);
+
+impl DefaultGltfImageSampler {
+    /// Creates a new [`DefaultGltfImageSampler`].
+    pub fn new(descriptor: &ImageSamplerDescriptor) -> Self {
+        Self(Arc::new(Mutex::new(descriptor.clone())))
+    }
+
+    /// Returns the current default [`ImageSamplerDescriptor`].
+    pub fn get(&self) -> ImageSamplerDescriptor {
+        self.0.lock().unwrap().clone()
+    }
+
+    /// Makes a clone of internal [`Arc`] pointer.
+    ///
+    /// Intended only to be used by code with no access to ECS.
+    pub fn get_internal(&self) -> Arc<Mutex<ImageSamplerDescriptor>> {
+        self.0.clone()
+    }
+
+    /// Replaces default [`ImageSamplerDescriptor`].
+    ///
+    /// Doesn't apply to samplers already built on top of it, i.e. `GltfLoader`'s output.
+    /// Assets need to manually be reloaded.
+    pub fn set(&self, descriptor: &ImageSamplerDescriptor) {
+        *self.0.lock().unwrap() = descriptor.clone();
+    }
+}
+
 /// Adds support for glTF file loading to the app.
-#[derive(Default)]
 pub struct GltfPlugin {
-    custom_vertex_attributes: HashMap<Box<str>, MeshVertexAttribute>,
+    /// The default image sampler to lay glTF sampler data on top of.
+    ///
+    /// Can be modified with [`DefaultGltfImageSampler`] resource.
+    pub default_sampler: ImageSamplerDescriptor,
+    /// Registry for custom vertex attributes.
+    ///
+    /// To specify, use [`GltfPlugin::add_custom_vertex_attribute`].
+    pub custom_vertex_attributes: HashMap<Box<str>, MeshVertexAttribute>,
+}
+
+impl Default for GltfPlugin {
+    fn default() -> Self {
+        GltfPlugin {
+            default_sampler: ImageSamplerDescriptor::linear(),
+            custom_vertex_attributes: HashMap::default(),
+        }
+    }
 }
 
 impl GltfPlugin {
@@ -157,9 +208,13 @@ impl Plugin for GltfPlugin {
             Some(render_device) => CompressedImageFormats::from_features(render_device.features()),
             None => CompressedImageFormats::NONE,
         };
+        let default_sampler_resource = DefaultGltfImageSampler::new(&self.default_sampler);
+        let default_sampler = default_sampler_resource.get_internal();
+        app.insert_resource(default_sampler_resource);
         app.register_asset_loader(GltfLoader {
             supported_compressed_formats,
             custom_vertex_attributes: self.custom_vertex_attributes.clone(),
+            default_sampler,
         });
     }
 }

crates/bevy_gltf/src/loader/gltf_ext/texture.rs

@@ -39,48 +39,48 @@ pub(crate) fn texture_handle(
 }
 
 /// Extracts the texture sampler data from the glTF [`Texture`].
-pub(crate) fn texture_sampler(texture: &Texture<'_>) -> ImageSamplerDescriptor {
+pub(crate) fn texture_sampler(
+    texture: &Texture<'_>,
+    default_sampler: &ImageSamplerDescriptor,
+) -> ImageSamplerDescriptor {
     let gltf_sampler = texture.sampler();
+    let mut sampler = default_sampler.clone();
 
-    ImageSamplerDescriptor {
-        address_mode_u: address_mode(&gltf_sampler.wrap_s()),
-        address_mode_v: address_mode(&gltf_sampler.wrap_t()),
-
-        mag_filter: gltf_sampler
-            .mag_filter()
-            .map(|mf| match mf {
-                MagFilter::Nearest => ImageFilterMode::Nearest,
-                MagFilter::Linear => ImageFilterMode::Linear,
-            })
-            .unwrap_or(ImageSamplerDescriptor::default().mag_filter),
-
-        min_filter: gltf_sampler
-            .min_filter()
-            .map(|mf| match mf {
-                MinFilter::Nearest
-                | MinFilter::NearestMipmapNearest
-                | MinFilter::NearestMipmapLinear => ImageFilterMode::Nearest,
-                MinFilter::Linear
-                | MinFilter::LinearMipmapNearest
-                | MinFilter::LinearMipmapLinear => ImageFilterMode::Linear,
-            })
-            .unwrap_or(ImageSamplerDescriptor::default().min_filter),
+    sampler.address_mode_u = address_mode(&gltf_sampler.wrap_s());
+    sampler.address_mode_v = address_mode(&gltf_sampler.wrap_t());
 
-        mipmap_filter: gltf_sampler
-            .min_filter()
-            .map(|mf| match mf {
-                MinFilter::Nearest
-                | MinFilter::Linear
-                | MinFilter::NearestMipmapNearest
-                | MinFilter::LinearMipmapNearest => ImageFilterMode::Nearest,
-                MinFilter::NearestMipmapLinear | MinFilter::LinearMipmapLinear => {
-                    ImageFilterMode::Linear
-                }
-            })
-            .unwrap_or(ImageSamplerDescriptor::default().mipmap_filter),
-
-        ..Default::default()
+    // Shouldn't parse filters when anisotropic filtering is on, because trilinear is then required by wgpu.
+    // We also trust user to have provided a valid sampler.
+    if sampler.anisotropy_clamp != 1 {
+        if let Some(mag_filter) = gltf_sampler.mag_filter().map(|mf| match mf {
+            MagFilter::Nearest => ImageFilterMode::Nearest,
+            MagFilter::Linear => ImageFilterMode::Linear,
+        }) {
+            sampler.mag_filter = mag_filter;
+        }
+        if let Some(min_filter) = gltf_sampler.min_filter().map(|mf| match mf {
+            MinFilter::Nearest
+            | MinFilter::NearestMipmapNearest
+            | MinFilter::NearestMipmapLinear => ImageFilterMode::Nearest,
+            MinFilter::Linear | MinFilter::LinearMipmapNearest | MinFilter::LinearMipmapLinear => {
+                ImageFilterMode::Linear
+            }
+        }) {
+            sampler.min_filter = min_filter;
+        }
+        if let Some(mipmap_filter) = gltf_sampler.min_filter().map(|mf| match mf {
+            MinFilter::Nearest
+            | MinFilter::Linear
+            | MinFilter::NearestMipmapNearest
+            | MinFilter::LinearMipmapNearest => ImageFilterMode::Nearest,
+            MinFilter::NearestMipmapLinear | MinFilter::LinearMipmapLinear => {
+                ImageFilterMode::Linear
+            }
+        }) {
+            sampler.mipmap_filter = mipmap_filter;
+        }
     }
+    sampler
 }
 
 pub(crate) fn texture_label(texture: &Texture<'_>) -> GltfAssetLabel {

crates/bevy_gltf/src/loader/mod.rs

@@ -1,9 +1,11 @@
 mod extensions;
 mod gltf_ext;
 
+use alloc::sync::Arc;
 use std::{
     io::Error,
     path::{Path, PathBuf},
+    sync::Mutex,
 };
 
 #[cfg(feature = "bevy_animation")]
@@ -146,6 +148,8 @@ pub struct GltfLoader {
     /// See [this section of the glTF specification](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes-overview)
     /// for additional details on custom attributes.
     pub custom_vertex_attributes: HashMap<Box<str>, MeshVertexAttribute>,
+    /// Arc to default [`ImageSamplerDescriptor`].
+    pub default_sampler: Arc<Mutex<ImageSamplerDescriptor>>,
 }
 
 /// Specifies optional settings for processing gltfs at load time. By default, all recognized contents of
@@ -181,6 +185,12 @@ pub struct GltfLoaderSettings {
     pub load_lights: bool,
     /// If true, the loader will include the root of the gltf root node.
     pub include_source: bool,
+    /// Overrides the default sampler. Data from sampler node is added on top of that.
+    ///
+    /// If None, uses global default which is stored in `DefaultGltfImageSampler` resource.
+    pub default_sampler: Option<ImageSamplerDescriptor>,
+    /// If true, the loader will ignore sampler data from gltf and use the default sampler.
+    pub override_sampler: bool,
 }
 
 impl Default for GltfLoaderSettings {
@@ -191,6 +201,8 @@ impl Default for GltfLoaderSettings {
             load_cameras: true,
             load_lights: true,
             include_source: false,
+            default_sampler: None,
+            override_sampler: false,
         }
     }
 }
@@ -506,6 +518,10 @@ async fn load_gltf<'a, 'b, 'c>(
         (animations, named_animations, animation_roots)
     };
 
+    let default_sampler = match settings.default_sampler.as_ref() {
+        Some(sampler) => sampler,
+        None => &loader.default_sampler.lock().unwrap().clone(),
+    };
     // We collect handles to ensure loaded images from paths are not unloaded before they are used elsewhere
     // in the loader. This prevents "reloads", but it also prevents dropping the is_srgb context on reload.
     //
@@ -522,7 +538,8 @@ async fn load_gltf<'a, 'b, 'c>(
                 &linear_textures,
                 parent_path,
                 loader.supported_compressed_formats,
-                settings.load_materials,
+                default_sampler,
+                settings,
             )
             .await?;
             image.process_loaded_texture(load_context, &mut _texture_handles);
@@ -542,7 +559,8 @@ async fn load_gltf<'a, 'b, 'c>(
                             linear_textures,
                             parent_path,
                             loader.supported_compressed_formats,
-                            settings.load_materials,
+                            default_sampler,
+                            settings,
                         )
                         .await
                     });
@@ -958,10 +976,15 @@ async fn load_image<'a, 'b>(
     linear_textures: &HashSet<usize>,
     parent_path: &'b Path,
     supported_compressed_formats: CompressedImageFormats,
-    render_asset_usages: RenderAssetUsages,
+    default_sampler: &ImageSamplerDescriptor,
+    settings: &GltfLoaderSettings,
 ) -> Result<ImageOrPath, GltfError> {
     let is_srgb = !linear_textures.contains(&gltf_texture.index());
-    let sampler_descriptor = texture_sampler(&gltf_texture);
+    let sampler_descriptor = if settings.override_sampler {
+        default_sampler.clone()
+    } else {
+        texture_sampler(&gltf_texture, default_sampler)
+    };
 
     match gltf_texture.source().source() {
         Source::View { view, mime_type } => {
@@ -974,7 +997,7 @@ async fn load_image<'a, 'b>(
                 supported_compressed_formats,
                 is_srgb,
                 ImageSampler::Descriptor(sampler_descriptor),
-                render_asset_usages,
+                settings.load_materials,
             )?;
             Ok(ImageOrPath::Image {
                 image,
@@ -996,7 +1019,7 @@ async fn load_image<'a, 'b>(
                         supported_compressed_formats,
                         is_srgb,
                         ImageSampler::Descriptor(sampler_descriptor),
-                        render_asset_usages,
+                        settings.load_materials,
                     )?,
                     label: GltfAssetLabel::Texture(gltf_texture.index()),
                 })