From c0f41045dafe1a2c25b2976464732704db7804c6 Mon Sep 17 00:00:00 2001
From: nullprop <git@nullprop.sh>
Date: Fri, 10 Nov 2023 20:09:20 +0200
Subject: [PATCH] Fix fog scene depth comparison

---
 res/shaders/fog.wgsl | 22 ++++++++--------------
 src/core/camera.rs   |  5 +++--
 src/core/state.rs    |  6 ++----
 3 files changed, 13 insertions(+), 20 deletions(-)

diff --git a/res/shaders/fog.wgsl b/res/shaders/fog.wgsl
index 304f146..bded66e 100644
--- a/res/shaders/fog.wgsl
+++ b/res/shaders/fog.wgsl
@@ -85,23 +85,18 @@ fn depth_to_linear(depth: f32) -> f32 {
 
 @fragment
 fn fs_main(vert: FogVertexOutput) -> @location(0) vec4<f32> {
-    let cam_to_volume = vert.world_position.xyz - camera.position.xyz;
-    var distance_to_volume = length(cam_to_volume);
-    let direction = cam_to_volume / distance_to_volume;
-    // FIXME: geom depth should always be greater than the volume surface depth...
-    // why is this broken?
-    distance_to_volume = depth_to_linear(vert.clip_position.z);
-    let uv = vert.clip_position.xy / camera.planes.xy;
-    let depth = textureSample(t_geometry_depth, s_geometry_depth, uv);
-    let geometry_depth = depth_to_linear(depth) - distance_to_volume;
-    if (geometry_depth <= 0.0)
+    let direction = normalize(vert.world_position.xyz - camera.position.xyz);
+    let volume_depth = depth_to_linear(vert.clip_position.z);
+    let uv = vert.clip_position.xy / camera.planes.zw;
+    let geometry_depth = depth_to_linear(textureSample(t_geometry_depth, s_geometry_depth, uv));
+    let max_fog_depth = geometry_depth - volume_depth;
+    if (max_fog_depth <= 0.0)
     {
         return vec4<f32>(0.0);
     }
-    return vec4<f32>(1.0);
 
-    /*
-    let density = ray_march(vert.world_position.xyz, direction, geometry_depth);
+    let density = ray_march(vert.world_position.xyz, direction, max_fog_depth);
+//    return vec4<f32>(1.0, 1.0, 1.0, density);
 
     var in_light = 0.0;
     if (global_uniforms.use_shadowmaps > 0u) {
@@ -153,5 +148,4 @@ fn fs_main(vert: FogVertexOutput) -> @location(0) vec4<f32> {
     result = result / (result + vec3(1.0));
 
     return vec4(result, density * FOG_ALPHA);
-    */
 }
diff --git a/src/core/camera.rs b/src/core/camera.rs
index c6c5320..fc8c09e 100644
--- a/src/core/camera.rs
+++ b/src/core/camera.rs
@@ -118,11 +118,11 @@ impl CameraUniform {
             proj: cgmath::Matrix4::identity().into(),
             inv_view_proj: cgmath::Matrix4::identity().into(),
             position: [0.0; 4],
-            planes: [NEAR_PLANE, FAR_PLANE, 0.0, 0.0],
+            planes: [NEAR_PLANE, FAR_PLANE, 1.0, 1.0],
         }
     }
 
-    pub fn update(&mut self, camera: &Camera) {
+    pub fn update(&mut self, camera: &Camera, config: &wgpu::SurfaceConfiguration) {
         let view = camera.get_view_matrix();
         let proj = camera.projection.get_matrix();
         self.view = view.into();
@@ -130,6 +130,7 @@ impl CameraUniform {
         let inv_view_proj = (proj * view).invert().unwrap();
         self.inv_view_proj = inv_view_proj.into();
         self.position = camera.position.to_homogeneous().into();
+        self.planes = [NEAR_PLANE, FAR_PLANE, config.width as f32, config.height as f32];
     }
 }
 
diff --git a/src/core/state.rs b/src/core/state.rs
index 26dc507..1623730 100644
--- a/src/core/state.rs
+++ b/src/core/state.rs
@@ -45,7 +45,6 @@ pub struct State {
     fog_instances: Vec<Instance>,
     fog_instance_buffer: wgpu::Buffer,
     geometry_depth_texture: Texture,
-    light_depth_texture: Texture,
     geom_model: Model,
     fog_model: Model,
     light_model: Model,
@@ -118,7 +117,7 @@ impl State {
         );
 
         let mut camera_uniform = CameraUniform::new();
-        camera_uniform.update(&camera);
+        camera_uniform.update(&camera, &config);
 
         let camera_buffer = device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
             label: Some("Camera Buffer"),
@@ -500,7 +499,6 @@ impl State {
             fog_instances,
             fog_instance_buffer,
             geometry_depth_texture,
-            light_depth_texture,
             geom_model,
             fog_model,
             light_model,
@@ -575,7 +573,7 @@ impl State {
         // Update camera
         self.camera.update(dt, &self.camera_controller);
         self.camera_controller.reset(false);
-        self.camera_uniform.update(&self.camera);
+        self.camera_uniform.update(&self.camera, &self.config);
         self.queue.write_buffer(
             &self.camera_buffer,
             0,