From 07d204fd6631ae0d0bfec16c8d057cd39c5ab810 Mon Sep 17 00:00:00 2001
From: yum <yum.food.vr@gmail.com>
Date: Tue, 3 Jun 2025 22:37:12 -0700
Subject: Continue work on fog

Fix screen uv calculation
---
 fog.cginc | 58 ++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 40 insertions(+), 18 deletions(-)

(limited to 'fog.cginc')

diff --git a/fog.cginc b/fog.cginc
index c0800bc..db90f8c 100644
--- a/fog.cginc
+++ b/fog.cginc
@@ -10,6 +10,7 @@
 struct FogParams {
     float steps;
     float density;
+    float y_cutoff;
     texture2D dithering_noise;
     texture3D density_noise;
     float4 density_noise_scale;
@@ -17,31 +18,52 @@ struct FogParams {
 
 struct FogResult {
     float4 color;
+    float depth;
 };
 
-float getRayLengthWorld()
+FogResult raymarched_fog(v2f i, FogParams p)
 {
-  float2 screen_uv;
-  float perspective_factor;
-  {
-    float3 full_vec_eye_to_geometry = i.worldPos - _WorldSpaceCameraPos;
-    float3 world_dir = normalize(i.worldPos - _WorldSpaceCameraPos);
-    float perspective_divide = 1.0 / i.pos.w;
-    perspective_factor = length(full_vec_eye_to_geometry * perspective_divide);
-    screen_uv = i.screenPos.xy * perspective_divide;
+  float3 ro = _WorldSpaceCameraPos;
+  float3 rd = normalize(i.eyeVec.xyz);
+
+  ro += rd * 1E-3;
+
+  float2 screen_uv = (i.pos.xy + 0.5) / _ScreenParams.xy;
+  float zDepthFromMap = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, screen_uv);
+  float linearZ =
+    GetLinearZFromZDepth_WorksWithMirrors(zDepthFromMap, screen_uv);
+  linearZ = min(1E3, linearZ);
+
+  // Get intersection with plane at elevation y.
+  float plane_y = -10;
+  float distance_to_y = 1E3;
+  if (abs(rd.y) > 1E-6) {
+    float t = (plane_y - ro.y) / rd.y;
+    if (t > 0) {
+      distance_to_y = min(t, 1E3);
+    }
   }
-  float eye_depth_world =
-    GetLinearZFromZDepth_WorksWithMirrors(
-        SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, screen_uv),
-        screen_uv) * perspective_factor;
-}
+  linearZ = min(linearZ, distance_to_y);
 
-FogResult raymarched_fog(v2f i, FogParams params)
-{
-    float3 ro = _WorldSpaceCameraPos;
-    float3 rd = normalize(i.worldPos - ray_pos);
+  float step_size = linearZ / p.steps;
+  float3 pp = ro;
+  float d = 0;
+  for (uint ii = 0; ii < p.steps; ++ii) {
+    pp += step_size * rd;
+    float cur_d = p.density_noise.SampleLevel(linear_repeat_s,
+        pp * p.density_noise_scale.xyz, 0);
+    cur_d *= p.density * step_size;
 
+    d = d + (1 - d) * cur_d;
+  }
 
+  FogResult r;
+  r.color.rgb = 1;
+  r.color.rgb = saturate(log(linearZ) / 5.0);
+  //r.color.a = saturate(d);
+  r.color.a = 1;
+  r.depth = 0.0001;  // Very small depth value to render in front
+  return r;
 }
 
 #endif  // _RAYMARCHED_FOG
-- 
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