From 499e6ded4187ffd5b89f80a440c935b3f5a44c9e Mon Sep 17 00:00:00 2001
From: hheik <4469778+hheik@users.noreply.github.com>
Date: Thu, 7 Dec 2023 17:03:59 +0200
Subject: [PATCH] wip: Software shadows to corners only

---
 src/game/darkness.rs | 88 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 76 insertions(+), 12 deletions(-)

diff --git a/src/game/darkness.rs b/src/game/darkness.rs
index 689d6d6..4147a04 100644
--- a/src/game/darkness.rs
+++ b/src/game/darkness.rs
@@ -20,7 +20,7 @@ pub use material::*;
 // Needs to be the same as in darkness.wgsl
 pub const MAX_POINT_LIGHTS: usize = 64;
 pub const MAX_SPOT_LIGHTS: usize = 64;
-pub const SHADOWMAP_RESOLUTION: usize = 256;
+pub const SHADOWMAP_RESOLUTION: usize = 1024;
 
 pub struct DarknessPlugin;
 
@@ -33,7 +33,7 @@ impl Plugin for DarknessPlugin {
             .register_asset_reflect::<DarknessMaterial>()
             .add_plugins(Material2dPlugin::<DarknessMaterial>::default())
             .add_systems(Update, add_to_level)
-            .add_systems(Last, prepare_lights);
+            .add_systems(Last, (prepare_lights, prepare_shadows).chain());
     }
 }
 
@@ -96,6 +96,7 @@ pub struct ShadowVertex {
 #[derive(Component, Reflect, Default, Debug, Clone)]
 #[reflect(Component)]
 pub struct ShadowMesh {
+    pub light_index: usize,
     pub vertices: Vec<ShadowVertex>,
 }
 
@@ -236,6 +237,7 @@ fn prepare_lights(
                 );
 
                 if let Ok(mut shadow_mesh) = shadow_mesh_query.get_mut(*entity) {
+                    shadow_mesh.light_index = i;
                     shadow_mesh.vertices = polygon
                         .iter()
                         .map(|point| ShadowVertex {
@@ -270,16 +272,6 @@ fn prepare_lights(
                     position: transform.translation().truncate(),
                     radius: light.radius,
                 };
-                // TODO: Remove when shadowmapping is done
-                for x in 0..SHADOWMAP_RESOLUTION {
-                    let offset = (i * SHADOWMAP_RESOLUTION + x) * 4;
-                    let distance = light.radius;
-                    let distance_bytes = bytes_of(&distance);
-                    shadowmap.data[offset + 0] = distance_bytes[0];
-                    shadowmap.data[offset + 1] = distance_bytes[1];
-                    shadowmap.data[offset + 2] = distance_bytes[2];
-                    shadowmap.data[offset + 3] = distance_bytes[3];
-                }
             });
 
         material.spot_light_count = spot_lights.len() as i32;
@@ -310,6 +302,78 @@ fn prepare_lights(
     }
 }
 
+fn prepare_shadows(
+    mut materials: ResMut<Assets<DarknessMaterial>>,
+    mut images: ResMut<Assets<Image>>,
+    shadow_mesh_query: Query<(&ShadowMesh, &GlobalTransform), Changed<ShadowMesh>>,
+    material_query: Query<&Handle<DarknessMaterial>>,
+) {
+    // TODO: Check that the shadow mesh overlaps the darkness material
+    for handle in &material_query {
+        let material = match materials.get_mut(handle) {
+            Some(material) => material,
+            None => continue,
+        };
+
+        let shadowmap = match &material.shadowmap_texture {
+            Some(handle) => match images.get_mut(&handle) {
+                Some(image) => image,
+                None => continue,
+            },
+            None => continue,
+        };
+
+        for (shadow_mesh, global_transform) in &shadow_mesh_query {
+            let shadow_map = calculate_shadow_map(
+                global_transform.translation().truncate(),
+                &shadow_mesh.vertices,
+            );
+            for x in 0..SHADOWMAP_RESOLUTION {
+                let offset = (shadow_mesh.light_index * SHADOWMAP_RESOLUTION + x) * 4;
+                let distance_bytes = bytes_of(&shadow_map[x]);
+                shadowmap.data[offset + 0] = distance_bytes[0];
+                shadowmap.data[offset + 1] = distance_bytes[1];
+                shadowmap.data[offset + 2] = distance_bytes[2];
+                shadowmap.data[offset + 3] = distance_bytes[3];
+            }
+        }
+    }
+}
+
+fn calculate_shadow_map(
+    global_position: Vec2,
+    vertices: &Vec<ShadowVertex>,
+) -> [f32; SHADOWMAP_RESOLUTION] {
+    let mut shadow_map = [0.0; SHADOWMAP_RESOLUTION];
+    let mut next_index = 0;
+    for x in 0..SHADOWMAP_RESOLUTION {
+        let angle = (x as f32 / SHADOWMAP_RESOLUTION as f32) * 2.0 * std::f32::consts::PI
+            - std::f32::consts::PI;
+
+        let prev_vertex = if next_index == 0 {
+            vertices[vertices.len() - 1]
+        } else {
+            vertices[(next_index - 1) % vertices.len()]
+        };
+        let next_vertex = vertices[next_index % vertices.len()];
+        if angle >= next_vertex.angle && next_index < vertices.len() {
+            next_index += 1;
+        }
+
+        let mut relative_angle = angle - prev_vertex.angle;
+        // Technically not correct, but works
+        if relative_angle < 0.0 {
+            relative_angle =
+                (std::f32::consts::PI - prev_vertex.angle) + (angle + std::f32::consts::PI);
+        }
+
+        // TODO: Calculate between-points
+        let distance = (next_vertex.point - global_position).length();
+        shadow_map[x] = distance;
+    }
+    shadow_map
+}
+
 fn get_light_geometry(
     rapier_context: &Res<RapierContext>,
     visibility_blocker_query: &Query<&VisibilityBlocker>,