From 054c967e4a06bbbf79359bae701e1b467625839c Mon Sep 17 00:00:00 2001
From: Kai Stevenson <kai@kaistevenson.com>
Date: Wed, 9 Sep 2026 22:29:14 -0700
Subject: lighting

---
 src/shader/instance.wgsl | 22 +++++++++++++++++++++-
 src/shader/lpv.wgsl      | 31 +++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 src/shader/lpv.wgsl

(limited to 'src/shader')

diff --git a/src/shader/instance.wgsl b/src/shader/instance.wgsl
index a549801..4b921ab 100644
--- a/src/shader/instance.wgsl
+++ b/src/shader/instance.wgsl
@@ -1,8 +1,16 @@
+const AMBIENT_LIGHT = vec4f(0.4, 0.4, 0.4, 1.0);
+const LIGHT_RESOLUTION = 1.0;
+
 struct Camera {
     scale: vec2f,
     centre: vec2f,
 };
 
+struct Lighting {
+    origin: vec2f,
+    _padding: vec2f,
+};
+
 struct Instance {
     centre: vec2f,
     cos_sin: vec2f,
@@ -15,6 +23,9 @@ struct Instance {
 @group(0) @binding(1) var<storage, read> palette: array<vec4f>;
 @group(0) @binding(2) var<storage, read> instances: array<Instance>;
 @group(0) @binding(3) var<storage, read> cells: array<u32>;
+@group(0) @binding(4) var lighting: texture_2d_array<f32>;
+@group(0) @binding(5) var light_sampler: sampler;
+@group(0) @binding(6) var<uniform> light_params: Lighting;
 
 struct VertexOutput {
     @builtin(position) clip_position: vec4f,
@@ -67,5 +78,14 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4f {
         discard;
     }
 
-    return palette[material];
+    var total = vec3f(0.0);
+    let light_dims = vec2f(textureDimensions(lighting));
+    let light_texel = (in.world - light_params.origin) * LIGHT_RESOLUTION;
+    let light_uv = light_texel / light_dims;
+    for (var d = 0u; d < 4u; d++) {
+        total += textureSample(lighting, light_sampler, light_uv, d).rgb;
+    }
+    let light = vec4f(total.r, total.g, total.b, 1.0);
+
+    return palette[material] * (light + AMBIENT_LIGHT);
 }
diff --git a/src/shader/lpv.wgsl b/src/shader/lpv.wgsl
new file mode 100644
index 0000000..1f84e40
--- /dev/null
+++ b/src/shader/lpv.wgsl
@@ -0,0 +1,31 @@
+const DIRS = array<vec2i, 4>(vec2i(1, 0), vec2i(0, 1), vec2i(-1, 0), vec2i(0, -1));
+const ATTEN: f32 = 0.999;
+const W_FWD: f32 = 0.70;
+const W_SIDE: f32 = 0.15;
+
+@group(0) @binding(0) var scene: texture_2d<f32>;
+@group(0) @binding(1) var src: texture_2d_array<f32>;
+@group(0) @binding(2) var dst: texture_storage_2d_array<rgba16float, write>;
+
+@compute @workgroup_size(8, 8, 1)
+fn propagate(@builtin(global_invocation_id) gid: vec3<u32>) {
+    let dims = textureDimensions(dst);
+    if gid.x >= dims.x || gid.y >= dims.y {
+        return;
+    }
+
+    let p = vec2<i32>(gid.xy);
+    let s = textureLoad(scene, p, 0);
+    let t = s.a;
+
+    for (var d = 0u; d < 4u; d++) {
+        let q = p - DIRS[d];
+        var inc = vec3f(0.0);
+        inc += textureLoad(src, q, d, 0).rgb * W_FWD;
+        inc += textureLoad(src, q, (d + 1u) % 4u, 0).rgb * W_SIDE;
+        inc += textureLoad(src, q, (d + 3u) % 4u, 0).rgb * W_SIDE;
+
+        let o = inc * t * ATTEN + s.rgb * 0.25;
+        textureStore(dst, p, d, vec4f(o, 1.0));
+    }
+}
\ No newline at end of file
-- 
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