//! A shader that uses the GLSL shading language.

use bevy::{
    prelude::*,
    reflect::TypePath,
    render::render_resource::{AsBindGroup, ShaderRef},
};

/// This example uses shader source files from the assets subdirectory
const VERTEX_SHADER_ASSET_PATH: &str = "shaders/custom_material.vert";
const FRAGMENT_SHADER_ASSET_PATH: &str = "shaders/custom_material.frag";

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(MaterialPlugin::<CustomMaterial>::default())
        .add_systems(Startup, setup)
        .run();
}

/// set up a simple 2D-screen-like surface
fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<CustomMaterial>>,
) {
    // Fullscreen flat surface: use a very large, thin cuboid so it behaves like a plane
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::default())),
        MeshMaterial3d(materials.add(CustomMaterial {
            color: LinearRgba::new(0.2, 0.6, 0.9, 1.0),
            color_texture: None,
            alpha_mode: AlphaMode::Opaque,
        })),
        // Scale X/Y large to cover the camera view, keep Z very small to make it effectively a plane
        Transform::from_scale(Vec3::new(2000.0, 2000.0, 0.01)),
    ));

    // 2D camera so the scene renders as a flat screen
    commands.spawn((Camera2d::default(), Transform::default()));
}

// This is the struct that will be passed to your shader
#[derive(Asset, TypePath, AsBindGroup, Clone)]
struct CustomMaterial {
    #[uniform(0)]
    color: LinearRgba,
    #[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!
/// When using the GLSL shading language for your shader, the specialize method must be overridden.
impl Material for CustomMaterial {
    fn vertex_shader() -> ShaderRef {
        VERTEX_SHADER_ASSET_PATH.into()
    }

    fn fragment_shader() -> ShaderRef {
        FRAGMENT_SHADER_ASSET_PATH.into()
    }

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