From 2d99ae5fff253f410c22595948840837eb962936 Mon Sep 17 00:00:00 2001
From: yvt <i@yvt.jp>
Date: Fri, 29 Jan 2021 19:04:05 +0900
Subject: [PATCH] feat(draw): fade the radiosity term above the `z = 0` plane

---
 Resources/Shaders/PostFilters/Fog2.fs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Resources/Shaders/PostFilters/Fog2.fs b/Resources/Shaders/PostFilters/Fog2.fs
index ddec24b3..a041d9f2 100644
--- a/Resources/Shaders/PostFilters/Fog2.fs
+++ b/Resources/Shaders/PostFilters/Fog2.fs
@@ -109,6 +109,8 @@ void main() {
 	vec3 ambientShadowTextureCoordDelta =
 	  viewcentricWorldPosition.xyz / float(numSamples) / vec3(512., 512., 65.);
 	vec3 radiosityFactor = vec3(0.0);
+	float currentRadiosityCutoff = currentAmbientShadowTextureCoord.z * 10.0 + 1.0;
+	float radiosityCutoffDelta = ambientShadowTextureCoordDelta.z * 10.0;
 
 	currentAmbientShadowTextureCoord += ambientShadowTextureCoordDelta * dither;
 
@@ -124,13 +126,17 @@ void main() {
 		fogColorFactor += aoFactor * weight * 0.5;
 
 		// Secondary diffuse reflection sampling
+		//
+		// Since the radiosity texture doesn't have the information above the `z = 0` plane,
+		// gradually reduce the influence above the plane by multiplying `currentRadiosityCutoff`.
 		vec3 radiosity =
 		  DecodeRadiosityValue(texture3D(radiosityTexture, currentRadiosityTextureCoord).xyz);
-		radiosityFactor += radiosity * weight;
+		radiosityFactor += radiosity * (weight * clamp(currentRadiosityCutoff, 0.0, 1.0));
 
 		currentShadowPosition += shadowPositionDelta;
 		currentRadiosityTextureCoord += radiosityTextureCoordDelta;
 		currentAmbientShadowTextureCoord += ambientShadowTextureCoordDelta;
+		currentRadiosityCutoff += radiosityCutoffDelta;
 		weightSum += weight;
 
 		weight -= weightDelta;