Make global fog independent of view direction

For calculating the distance in fog in the global fog shader, only the
distance along the viewing axis was counted. This made it so there is
less fog when look at something from the corner of your eye than when
you look at it directly. This behavior matches fogQuake3 but there is
really no reason to do it. Count the whole distance instead of only
distance along view axis.

Author: slipher

src/engine/renderer/gl_shader.cpp

@@ -2639,7 +2639,8 @@ GLShader_fogGlobal::GLShader_fogGlobal() :
 	u_UnprojectMatrix( this ),
 	u_Color_Float( this ),
 	u_Color_Uint( this ),
-	u_FogDistanceVector( this )
+	u_ViewOrigin( this ),
+	u_FogDensity( this )
 {
 }
 

src/engine/renderer/gl_shader.h

@@ -3481,7 +3481,8 @@ class GLShader_fogGlobal :
 	public u_UnprojectMatrix,
 	public u_Color_Float,
 	public u_Color_Uint,
-	public u_FogDistanceVector
+	public u_ViewOrigin,
+	public u_FogDensity
 {
 public:
 	GLShader_fogGlobal();

src/engine/renderer/glsl_source/fogGlobal_fp.glsl

@@ -29,7 +29,8 @@ uniform sampler2D	u_DepthMap;
 
 uniform colorPack u_Color;
 
-uniform vec4		u_FogDistanceVector;
+uniform vec3 u_ViewOrigin;
+uniform float u_FogDensity;
 uniform mat4		u_UnprojectMatrix;
 
 DECLARE_OUTPUT(vec4)
@@ -45,7 +46,7 @@ void	main()
 	P.xyz /= P.w;
 
 	// calculate the length in fog (t is always 1 if eye is in fog)
-	st.s = dot(P.xyz, u_FogDistanceVector.xyz) + u_FogDistanceVector.w;
+	st.s = distance(u_ViewOrigin, P.xyz) * u_FogDensity;
 	st.t = 1.0;
 
 	vec4 color = texture2D(u_ColorMap, st);

src/engine/renderer/tr_backend.cpp

@@ -1377,20 +1377,8 @@ void RB_RenderGlobalFog()
 
 		GL_State( GLS_DEPTHTEST_DISABLE | GLS_SRCBLEND_SRC_ALPHA | GLS_DSTBLEND_ONE_MINUS_SRC_ALPHA );
 
-		// all fogging distance is based on world Z units
-		vec4_t fogDistanceVector;
-		vec3_t local;
-		VectorSubtract( backEnd.orientation.origin, backEnd.viewParms.orientation.origin, local );
-		fogDistanceVector[ 0 ] = -backEnd.orientation.modelViewMatrix[ 2 ];
-		fogDistanceVector[ 1 ] = -backEnd.orientation.modelViewMatrix[ 6 ];
-		fogDistanceVector[ 2 ] = -backEnd.orientation.modelViewMatrix[ 10 ];
-		fogDistanceVector[ 3 ] = DotProduct( local, backEnd.viewParms.orientation.axis[ 0 ] );
-
-		// scale the fog vectors based on the fog's thickness
-		VectorScale( fogDistanceVector, fog->tcScale, fogDistanceVector );
-		fogDistanceVector[ 3 ] *= fog->tcScale;
-
-		gl_fogGlobalShader->SetUniform_FogDistanceVector( fogDistanceVector );
+		gl_fogGlobalShader->SetUniform_FogDensity( fog->tcScale );
+		gl_fogGlobalShader->SetUniform_ViewOrigin( backEnd.viewParms.orientation.origin );
 		SetUniform_Color( gl_fogGlobalShader, fog->color );
 	}