wsg/lib/examples/shadow_test.rs

//! Dedicated test for **shadow mapping**.
//!
//! A single **directional** light is configured as the shadow caster
//! (`Scene::set_shadow_caster(Some(0))`). The cube sits on a large thin ground
//! slab, so its silhouette is projected as a crisp PCF-softened shadow. With a
//! small ambient term the shadow is clearly visible and the light/shadow
//! directions are easy to read:
//!
//!   1. the **blocker** (cube) casts a directional shadow that stretches along
//!      the ground opposite the light direction. The light sits at the camera's
//!      front-right and low-ish, so its shadow runs clearly across the ground to
//!      the left of the cube and is easy to see,
//!   2. the shadow edge is **softened** by 3×3 PCF (no hard jagged border),
//!   3. the lit faces are bright while the shadowed ground stays near-ambient,
//!      proving the depth comparison is applied per-pixel.
//!
//! Run with: `cargo run -p wsg-lib --example shadow_test`
use glam::Vec3;
use wsg_lib::resources::{Camera, Geometry};
use wsg_lib::utils::WsgError;

/// Shadow handler: a fixed scene (ground slab + cube blocker) lit by one
/// shadow-casting directional light.
struct ShadowTest;

/// Axis-aligned box geometry (24 vertices / 36 indices, per-face normals + uvs).
fn box_geometry(hx: f32, hy: f32, hz: f32) -> Geometry {
    let faces: [([f32; 3], [[f32; 3]; 4]); 6] = [
        (
            [0.0, 0.0, 1.0],
            [[-hx, -hy, hz], [hx, -hy, hz], [hx, hy, hz], [-hx, hy, hz]],
        ), // +Z
        (
            [0.0, 0.0, -1.0],
            [
                [hx, -hy, -hz],
                [-hx, -hy, -hz],
                [-hx, hy, -hz],
                [hx, hy, -hz],
            ],
        ), // -Z
        (
            [1.0, 0.0, 0.0],
            [[hx, -hy, -hz], [hx, hy, -hz], [hx, hy, hz], [hx, -hy, hz]],
        ), // +X
        (
            [-1.0, 0.0, 0.0],
            [
                [-hx, -hy, hz],
                [-hx, hy, hz],
                [-hx, hy, -hz],
                [-hx, -hy, -hz],
            ],
        ), // -X
        (
            [0.0, 1.0, 0.0],
            [[-hx, hy, -hz], [hx, hy, -hz], [hx, hy, hz], [-hx, hy, hz]],
        ), // +Y
        (
            [0.0, -1.0, 0.0],
            [
                [-hx, -hy, hz],
                [hx, -hy, hz],
                [hx, -hy, -hz],
                [-hx, -hy, -hz],
            ],
        ), // -Y
    ];

    let mut positions = Vec::with_capacity(24);
    let mut normals = Vec::with_capacity(24);
    let mut uvs = Vec::with_capacity(24);
    let quad_uvs = [[0.0, 0.0], [1.0, 0.0], [1.0, 1.0], [0.0, 1.0]];
    for (normal, corners) in faces {
        for (i, corner) in corners.iter().enumerate() {
            positions.push(*corner);
            normals.push(normal);
            uvs.push(quad_uvs[i]);
        }
    }
    let mut indices = Vec::with_capacity(36);
    for face in 0..6u16 {
        let b = face * 4;
        indices.extend_from_slice(&[b, b + 1, b + 2, b, b + 2, b + 3]);
    }
    Geometry::new(positions)
        .with_normals(normals)
        .with_uvs(uvs)
        .with_indices(indices)
}

impl wsg_lib::AppHandler for ShadowTest {
    fn setup(&mut self, app: &mut wsg_lib::App) {
        app.scene
            .register_shader("standard", wsg_lib::utils::STANDARD_SHADER_PATH)
            .unwrap();
        app.scene.add_material_shader("mat", "standard").unwrap();

        // Ground slab (thin, wide) lying with its top at y = 0.
        app.scene
            .create_mesh("ground_mesh", box_geometry(5.0, 0.05, 5.0), Some("mat"))
            .unwrap();
        app.scene
            .add_entity_with_transform(
                "ground",
                "ground_mesh",
                wsg_lib::math::Transform::identity(),
            )
            .unwrap();

        // Blocker cube centred at the origin, standing on the ground (bottom at y = 0).
        app.scene
            .create_mesh("cube_mesh", box_geometry(0.5, 0.5, 0.5), Some("mat"))
            .unwrap();
        let mut cube_tf = wsg_lib::math::Transform::identity();
        cube_tf.translation = Vec3::new(0.0, 0.5, 0.0);
        app.scene
            .add_entity_with_transform("cube", "cube_mesh", cube_tf)
            .unwrap();

        // One directional light only: replace the default list.
        app.scene.clear_lights();
        // Direction "from surface toward the light": the light sits up and to the +x side
        // (the camera's right), at a lowish elevation. Its shadow is then cast toward -x,
        // running clearly across the ground to the left of the cube. A steeper or more
        // frontal light would push the shadow tight against the cube's base or behind it,
        // where it is occluded by the cube from this elevated front-right view.
        let toward_light = Vec3::new(1.0, 0.5, 0.0).normalize();
        app.scene
            .add_directional_light(toward_light, [1.0, 0.98, 0.92], 1.6)
            .unwrap();

        // Make this directional light (packed index 0) the shadow caster.
        app.scene.set_shadow_caster(Some(0));

        // Small ambient so the shadowed side of the ground stays readable.
        app.scene.set_ambient([0.12, 0.12, 0.14]);

        // Slightly elevated view so both the cube and its ground shadow are framed.
        app.scene
            .set_camera(Camera::new(Vec3::new(3.4, 2.6, 3.4), Vec3::ZERO, Vec3::Y));
    }
}

#[pollster::main]
async fn main() -> Result<(), WsgError> {
    let app = wsg_lib::app::AppBuilder::new()
        .title("WSG Shadow Test")
        .build()
        .await?;
    app.run(ShadowTest)
}