How to use dynamic asset in Material?

[takkuumi]

This is Material example code

#[derive(Debug, Clone, TypeUuid, AsBindGroup)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CustomMaterial {
  #[uniform(0)]
  color: Color,
  #[texture(1)]
  #[sampler(2)]
  color_texture: Option<Handle<Image>>,
  alpha_mode: AlphaMode,
}

/// The Material trait is very configurable, but comes with sensible defaults for all methods.
/// You only need to implement functions for features that need non-default behavior. See the Material api docs for details!
impl Material for CustomMaterial {
  fn fragment_shader() -> ShaderRef {
    "shaders/custom_material.wgsl".into()
  }

  fn alpha_mode(&self) -> AlphaMode {
    self.alpha_mode
  }
}

When i want to pass a config of shader asset url into Material, but i dont know how to do it.

use bevy::{
  diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
  log::LogPlugin,
  prelude::*,
  reflect::TypeUuid,
  render::render_resource::{AsBindGroup, ShaderRef},
  window::PresentMode,
};
use wasm_bindgen::prelude::*;

#[derive(Resource, Default)]
pub struct AppConfig {
  pub asset_url: String,
}

impl AppConfig {
  pub fn new(url: String) -> Self {
    AppConfig { asset_url: url }
  }
}

#[wasm_bindgen]
pub struct VWindow {
  width: f32,
  height: f32,
  title: String,
  canvas: String,
}

#[wasm_bindgen]
impl VWindow {
  pub fn new(width: f32, height: f32, title: String, canvas: String) -> Self {
    Self {
      width,
      height,
      title,
      canvas,
    }
  }
}

#[wasm_bindgen]
pub fn init_bevy(win: VWindow, url: String) {
  init(win, AppConfig::new(url));
}


pub fn init(win: VWindow, config: AppConfig) {
  let VWindow {
    width,
    height,
    title,
    canvas,
  } = win;

  App::new()
    .add_plugins(DefaultPlugins.set(LogPlugin {
      filter: "info,wgpu_core=warn,wgpu_hal=warn,vgr=debug".into(),
      level: bevy::log::Level::DEBUG,
    }))
    .add_plugins(DefaultPlugins.set(WindowPlugin {
      window: WindowDescriptor {
        width,
        height,
        title,
        canvas: Some(canvas),
        present_mode: PresentMode::Fifo,
        ..Default::default()
      },
      ..Default::default()
    }))
    .add_plugins(DefaultPlugins)
    .add_plugin(LogDiagnosticsPlugin::default())
    .add_plugin(FrameTimeDiagnosticsPlugin::default())
    .add_plugin(MaterialPlugin::<CustomMaterial>::default())
    .add_startup_system(
      move |commands: Commands,
            meshes: ResMut<Assets<Mesh>>,
            materials: ResMut<Assets<CustomMaterial>>,
            asset_server: Res<AssetServer>| {
        setup(commands, meshes, materials, asset_server, &config)
      },
    )
    .run();
}

/// set up a simple 3D scene
fn setup(
  mut commands: Commands,
  mut meshes: ResMut<Assets<Mesh>>,
  mut materials: ResMut<Assets<CustomMaterial>>,
  asset_server: Res<AssetServer>,
  config: &AppConfig,
) {
  // cube
  commands.spawn(MaterialMeshBundle {
    mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
    transform: Transform::from_xyz(0.0, 0.5, 0.0),
    material: materials.add(CustomMaterial {
      color: Color::GREEN,
      color_texture: Some(asset_server.load("branding/icon.png")),
      alpha_mode: AlphaMode::Blend,
    }),

    ..default()
  });

  // camera
  commands.spawn(Camera3dBundle {
    transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
    ..default()
  });
}

// This is the struct that will be passed to your shader
#[derive(Debug, Clone, TypeUuid, AsBindGroup)]
#[uuid = "f690fdae-d598-45ab-8225-97e2a3f056e0"]
pub struct CustomMaterial {
  #[uniform(0)]
  color: Color,
  #[texture(1)]
  #[sampler(2)]
  color_texture: Option<Handle<Image>>,
  alpha_mode: AlphaMode,
}

/// The Material trait is very configurable, but comes with sensible defaults for all methods.
/// You only need to implement functions for features that need non-default behavior. See the Material api docs for details!
impl Material for CustomMaterial {
  fn fragment_shader() -> ShaderRef {
    "shaders/custom_material.wgsl".into()
  }

  fn alpha_mode(&self) -> AlphaMode {
    self.alpha_mode
  }
}

I want to use config.asset_url instead shaders/custom_material.wgsl, but the fragment_shader of Material has no param.
how to do it?