From 55d4c89753d96a226f739febf9e57e0fa2d7968d Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@zdoom.fake>
Date: Mon, 12 May 2014 14:58:37 +0200
Subject: [PATCH] - fixed: fog density calculation for fixed function was not
 correct.

---
 src/gl/renderer/gl_renderstate.cpp | 9 +++++----
 src/gl/renderer/gl_renderstate.h   | 1 -
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/gl/renderer/gl_renderstate.cpp b/src/gl/renderer/gl_renderstate.cpp
index 7efa1d30f3..746bbb1765 100644
--- a/src/gl/renderer/gl_renderstate.cpp
+++ b/src/gl/renderer/gl_renderstate.cpp
@@ -69,7 +69,7 @@ void FRenderState::Reset()
 	ffTextureEnabled = ffFogEnabled = false;
 	mSpecialEffect = ffSpecialEffect = EFF_NONE;
 	mFogColor.d = ffFogColor.d = -1;
-	mFogDensity = ffFogDensity = 0;
+	ffFogDensity = 0;
 	mTextureMode = ffTextureMode = -1;
 	mDesaturation = 0;
 	mSrcBlend = GL_SRC_ALPHA;
@@ -316,10 +316,11 @@ void FRenderState::Apply(bool forcenoshader)
 				GLfloat FogColor[4]={mFogColor.r/255.0f,mFogColor.g/255.0f,mFogColor.b/255.0f,0.0f};
 				glFogfv(GL_FOG_COLOR, FogColor);
 			}
-			if (ffFogDensity != mFogDensity)
+			if (ffFogDensity != mLightParms[2])
 			{
-				glFogf(GL_FOG_DENSITY, mFogDensity/64000.f);
-				ffFogDensity=mFogDensity;
+				const float LOG2E = 1.442692f;	// = 1/log(2)
+				glFogf(GL_FOG_DENSITY, -mLightParms[2] / LOG2E);
+				ffFogDensity = mLightParms[2];
 			}
 		}
 		if (mSpecialEffect != ffSpecialEffect)
diff --git a/src/gl/renderer/gl_renderstate.h b/src/gl/renderer/gl_renderstate.h
index e8de712f6b..888ead0d73 100644
--- a/src/gl/renderer/gl_renderstate.h
+++ b/src/gl/renderer/gl_renderstate.h
@@ -65,7 +65,6 @@ class FRenderState
 	PalEntry mFogColor;
 	PalEntry mObjectColor;
 	PalEntry mDynColor;
-	float mFogDensity;
 
 	int mEffectState;
 	int mColormapState;