From 13d33719f39976838d87d5beeb3cae3d52d2b003 Mon Sep 17 00:00:00 2001
From: past-due <30942300+past-due@users.noreply.github.com>
Date: Sun, 17 Mar 2024 20:25:37 -0400
Subject: [PATCH] Fix: Normal terrain quality water + fog, adjust blending

---
 data/base/shaders/vk/water.frag | 11 ++++++++---
 data/base/shaders/water.frag    | 11 ++++++++---
 lib/ivis_opengl/gfx_api_gl.cpp  |  2 +-
 lib/ivis_opengl/gfx_api_vk.cpp  |  6 +++---
 4 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/data/base/shaders/vk/water.frag b/data/base/shaders/vk/water.frag
index 063b23afc30..49523adfdb1 100644
--- a/data/base/shaders/vk/water.frag
+++ b/data/base/shaders/vk/water.frag
@@ -56,10 +56,15 @@ void main()
 	{
 		// Calculate linear fog
 		float fogFactor = (fogEnd - vertexDistance) / (fogEnd - fogStart);
-		fogFactor = clamp(fogFactor, 0.0, 1.0);
 
-		// Return fragment color
-		fragColor = mix(fragColor, fogColor, fogFactor);
+		if (fogFactor >= 1.f)
+		{
+			discard;
+		}
+
+		fogFactor = 1.0 - clamp(fogFactor, 0.0, 1.0);
+		fragColor.rgb *= fogFactor; // premultiply by fogFactor as alpha
+		fragColor.a = fogFactor;
 	}
 
 	FragColor = fragColor;
diff --git a/data/base/shaders/water.frag b/data/base/shaders/water.frag
index b15c64b8f34..0c045ed8812 100644
--- a/data/base/shaders/water.frag
+++ b/data/base/shaders/water.frag
@@ -65,10 +65,15 @@ void main()
 	{
 		// Calculate linear fog
 		float fogFactor = (fogEnd - vertexDistance) / (fogEnd - fogStart);
-		fogFactor = clamp(fogFactor, 0.0, 1.0);
 
-		// Return fragment color
-		fragColor = mix(fragColor, fogColor, fogFactor);
+		if (fogFactor >= 1.f)
+		{
+			discard;
+		}
+
+		fogFactor = 1.0 - clamp(fogFactor, 0.0, 1.0);
+		fragColor.rgb *= fogFactor; // premultiply by fogFactor as alpha
+		fragColor.a = fogFactor;
 	}
 
 	FragColor = fragColor;
diff --git a/lib/ivis_opengl/gfx_api_gl.cpp b/lib/ivis_opengl/gfx_api_gl.cpp
index 1d88ea09e84..25ba3b2df02 100644
--- a/lib/ivis_opengl/gfx_api_gl.cpp
+++ b/lib/ivis_opengl/gfx_api_gl.cpp
@@ -1269,7 +1269,7 @@ void gl_pipeline_state_object::bind()
 
 		case REND_MULTIPLICATIVE:
 			glEnable(GL_BLEND);
-			glBlendFunc(GL_ZERO, GL_SRC_COLOR);
+			glBlendFunc(GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA);
 			break;
 
 		case REND_PREMULTIPLIED:
diff --git a/lib/ivis_opengl/gfx_api_vk.cpp b/lib/ivis_opengl/gfx_api_vk.cpp
index bdcaadb16b9..72d5fd40aa8 100644
--- a/lib/ivis_opengl/gfx_api_vk.cpp
+++ b/lib/ivis_opengl/gfx_api_vk.cpp
@@ -1279,9 +1279,9 @@ std::array<vk::PipelineColorBlendAttachmentState, 1> VkPSO::to_vk(const REND_MOD
 				.setBlendEnable(true)
 				.setColorBlendOp(vk::BlendOp::eAdd)
 				.setAlphaBlendOp(vk::BlendOp::eAdd)
-				.setSrcColorBlendFactor(vk::BlendFactor::eZero)
-				.setSrcAlphaBlendFactor(vk::BlendFactor::eZero)
-				.setDstColorBlendFactor(vk::BlendFactor::eSrcColor)
+				.setSrcColorBlendFactor(vk::BlendFactor::eDstColor)
+				.setSrcAlphaBlendFactor(vk::BlendFactor::eDstAlpha)
+				.setDstColorBlendFactor(vk::BlendFactor::eOneMinusSrcAlpha)
 				.setDstAlphaBlendFactor(vk::BlendFactor::eOneMinusSrcAlpha)
 				.setColorWriteMask(vk_color_mask)
 		};