From b9b184020f587f837152e10a8647c985d9526d25 Mon Sep 17 00:00:00 2001
From: Vincent Lejeune <vljn.ovi@gmail.com>
Date: Sun, 14 Jan 2024 15:59:33 +0100
Subject: [PATCH] volumetric: support for volumetric fog added for terrain

---
 data/base/shaders/vk/pointlights.glsl         | 44 +++++++++++++++++++
 .../shaders/vk/terrain_combined_frag.glsl     |  6 +--
 .../shaders/vk/terrain_combined_high.frag     | 11 ++++-
 3 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/data/base/shaders/vk/pointlights.glsl b/data/base/shaders/vk/pointlights.glsl
index 8856b95f34b..87635f75b7c 100644
--- a/data/base/shaders/vk/pointlights.glsl
+++ b/data/base/shaders/vk/pointlights.glsl
@@ -74,6 +74,50 @@ vec4 iterateOverAllPointLights(
 	return light;
 }
 
+//volumetric
+vec4 volumetricIterateOverAllPointLights(
+	vec2 clipSpaceCoord,
+	vec3 cameraPosition,
+	vec3 WorldFragPos
+) {
+	vec3 result = vec3(0);
+	ivec2 bucket = ivec2(WZ_BUCKET_DIMENSION * clipSpaceCoord);
+	int bucketId = min(bucket.y + bucket.x * WZ_BUCKET_DIMENSION, WZ_BUCKET_DIMENSION * WZ_BUCKET_DIMENSION - 1);
+
+
+	vec3 viewLine = cameraPosition.xyz - WorldFragPos;
+	vec3 currentTransmittence = vec3(1);
+	vec3 transMittance = vec3(1);
+
+
+#define STEPS 64
+	for (int i = 0; i < STEPS; i++)
+	{
+		vec3 od = fogColor.xyz * length(viewLine / STEPS) / 10000;
+		vec3 posOnViewLine = WorldFragPos + viewLine * i / STEPS;
+
+
+		float sunLightEnergy = getShadowVisibility(posOnViewLine);
+		vec3 scatteredLight = vec3(sunLightEnergy) * od;
+
+		for (int i = 0; i < bucketOffsetAndSize[bucketId].y; i++)
+		{
+			int entryInLightList = bucketOffsetAndSize[bucketId].x + i;
+			int lightIndex = PointLightsIndex[entryInLightList / 4][entryInLightList % 4];
+			vec4 position = PointLightsPosition[lightIndex];
+			vec4 colorAndEnergy = PointLightsColorAndEnergy[lightIndex];
+			vec3 tmp = position.xyz * vec3(1., 1., -1.);
+			scatteredLight += colorAndEnergy.xyz * pointLightEnergyAtPosition(posOnViewLine, tmp, colorAndEnergy.w) * od;
+		}
+
+		result += scatteredLight * currentTransmittence;
+
+		currentTransmittence *= exp2(od);
+		transMittance *= exp2(-od);
+	}
+	return vec4(result * transMittance, transMittance);
+}
+
 vec3 toneMap(vec3 x)
 {
 	return x;
diff --git a/data/base/shaders/vk/terrain_combined_frag.glsl b/data/base/shaders/vk/terrain_combined_frag.glsl
index 287a4ab6916..57d7eb0f389 100644
--- a/data/base/shaders/vk/terrain_combined_frag.glsl
+++ b/data/base/shaders/vk/terrain_combined_frag.glsl
@@ -6,7 +6,7 @@ float getShadowMapDepthComp(vec2 base_uv, float u, float v, vec2 shadowMapSizeIn
 	return texture( shadowMap, vec4(uv, cascadeIndex, z) );
 }
 
-float getShadowVisibility()
+float getShadowVisibility(vec3 fragPos)
 {
 	if (WZ_SHADOW_MODE == 0 || WZ_SHADOW_FILTER_SIZE == 0)
 	{
@@ -17,7 +17,7 @@ float getShadowVisibility()
 	{
 		// Shadow Mapping
 
-		vec4 fragPosViewSpace = ViewMatrix * vec4(frag.fragPos, 1.0);
+		vec4 fragPosViewSpace = ViewMatrix * vec4(fragPos, 1.0);
 		float depthValue = abs(fragPosViewSpace.z);
 
 		int cascadeIndex = 0;
@@ -51,7 +51,7 @@ float getShadowVisibility()
 			}
 		}
 
-		vec4 shadowPos = ShadowMapMVPMatrix[cascadeIndex] * vec4(frag.fragPos, 1.0);
+		vec4 shadowPos = ShadowMapMVPMatrix[cascadeIndex] * vec4(fragPos, 1.0);
 		vec3 pos = shadowPos.xyz / shadowPos.w;
 
 		if (pos.z > 1.0f)
diff --git a/data/base/shaders/vk/terrain_combined_high.frag b/data/base/shaders/vk/terrain_combined_high.frag
index b0fb656d8d5..fca0ac85354 100644
--- a/data/base/shaders/vk/terrain_combined_high.frag
+++ b/data/base/shaders/vk/terrain_combined_high.frag
@@ -66,7 +66,7 @@ vec3 blendAddEffectLighting(vec3 a, vec3 b) {
 vec4 doBumpMapping(BumpData b, vec3 lightDir, vec3 halfVec) {
 	vec3 L = normalize(lightDir);
 	vec3 H = normalize(halfVec);
-	float visibility = getShadowVisibility();
+	float visibility = getShadowVisibility(frag.fragPos);
 
 	MaterialInfo materialInfo;
 	materialInfo.albedo = b.color;
@@ -125,6 +125,12 @@ void main()
 {
 	vec4 fragColor = main_bumpMapping();
 
+#if 1
+
+	vec2 clipSpaceCoord = gl_FragCoord.xy / vec2(viewportWidth, viewportHeight);	
+	vec4 volumetric = volumetricIterateOverAllPointLights(clipSpaceCoord, cameraPos.xyz, frag.fragPos);
+	fragColor.xyz = toneMap(fragColor.xyz * volumetric.a + volumetric.xyz);
+#else
 	if (fogEnabled > 0)
 	{
 		// Calculate linear fog
@@ -134,5 +140,6 @@ void main()
 		// Return fragment color
 		fragColor = mix(fragColor, vec4(fogColor.xyz, fragColor.w), fogFactor);
 	}
-	FragColor = vec4(toneMap(fragColor.xyz), fragColor.w);
+#endif
+	FragColor = fragColor;
 }