Fog: count full distance, not only along view axis

When calculating the distance from the viewer to a vertex in the
fogQuake3 shader, use the full distance, instead of dotting the
viewer-to-vertex vector with the view axis. So now all points on the
screen will be rendered consistently, instead of for example a point 30
degrees away from the center having its fog distance multiplied by
sqrt(2)/2 ~= 0.7.

Author: slipher

src/engine/renderer/Material.cpp

@@ -1089,15 +1089,6 @@ void BindShaderFog( Material* material ) {
 	// Set shader uniforms.
 	const fog_t* fog = tr.world->fogs + material->fog;
 
-	// all fogging distance is based on world Z units
-	vec4_t fogDistanceVector;
-	VectorCopy( backEnd.viewParms.orientation.axis[ 0 ], fogDistanceVector );
-	fogDistanceVector[ 3 ] = -DotProduct( fogDistanceVector, backEnd.viewParms.orientation.origin );
-
-	// scale the fog vectors based on the fog's thickness
-	VectorScale( fogDistanceVector, fog->tcScale, fogDistanceVector );
-	fogDistanceVector[3] *= fog->tcScale;
-
 	// rotate the gradient vector for this orientation
 	float eyeT;
 	vec4_t fogDepthVector;
@@ -1110,11 +1101,11 @@ void BindShaderFog( Material* material ) {
 		eyeT = 1; // non-surface fog always has eye inside
 	}
 
-	// see if the viewpoint is outside
-	// this is needed for clipping distance even for constant fog
-	fogDistanceVector[3] += 1.0 / 512;
+	// Note: things that seemingly should be per-shader or per-surface can be set as global uniforms
+	// since fognum is grouped with the GL state stuff, segregating each fognum in a separate draw call.
 
-	gl_fogQuake3ShaderMaterial->SetUniform_FogDistanceVector( fogDistanceVector );
+	gl_fogQuake3ShaderMaterial->SetUniform_ViewOrigin( backEnd.viewParms.orientation.origin );
+	gl_fogQuake3ShaderMaterial->SetUniform_FogDensity( fog->tcScale );
 	gl_fogQuake3ShaderMaterial->SetUniform_FogDepthVector( fogDepthVector );
 	gl_fogQuake3ShaderMaterial->SetUniform_FogEyeT( eyeT );
 

src/engine/renderer/gl_shader.cpp

@@ -2587,7 +2587,8 @@ GLShader_fogQuake3::GLShader_fogQuake3() :
 	u_ColorGlobal_Uint( this ),
 	u_Bones( this ),
 	u_VertexInterpolation( this ),
-	u_FogDistanceVector( this ),
+	u_ViewOrigin( this ),
+	u_FogDensity( this ),
 	u_FogDepthVector( this ),
 	u_FogEyeT( this ),
 	GLDeformStage( this ),
@@ -2608,7 +2609,8 @@ GLShader_fogQuake3Material::GLShader_fogQuake3Material() :
 	u_ModelMatrix( this ),
 	u_ModelViewProjectionMatrix( this ),
 	u_ColorGlobal_Uint( this ),
-	u_FogDistanceVector( this ),
+	u_ViewOrigin( this ),
+	u_FogDensity( this ),
 	u_FogDepthVector( this ),
 	u_FogEyeT( this ),
 	GLDeformStage( this ) {

src/engine/renderer/gl_shader.h

@@ -2112,7 +2112,7 @@ class u_FogDensity :
 {
 public:
 	u_FogDensity( GLShader *shader ) :
-		GLUniform1f( shader, "u_FogDensity" )
+		GLUniform1f( shader, "u_FogDensity", true )
 	{
 	}
 
@@ -2912,21 +2912,6 @@ template<typename Shader> void SetUniform_ColorModulateColorGen(
 	}
 }
 
-class u_FogDistanceVector :
-	GLUniform4f
-{
-public:
-	u_FogDistanceVector( GLShader *shader ) :
-		GLUniform4f( shader, "u_FogDistanceVector", true )
-	{
-	}
-
-	void SetUniform_FogDistanceVector( const vec4_t v )
-	{
-		this->SetValue( v );
-	}
-};
-
 class u_FogDepthVector :
 	GLUniform4f
 {
@@ -3448,7 +3433,8 @@ class GLShader_fogQuake3 :
 	public u_ColorGlobal_Uint,
 	public u_Bones,
 	public u_VertexInterpolation,
-	public u_FogDistanceVector,
+	public u_ViewOrigin,
+	public u_FogDensity,
 	public u_FogDepthVector,
 	public u_FogEyeT,
 	public GLDeformStage,
@@ -3466,7 +3452,8 @@ class GLShader_fogQuake3Material :
 	public u_ModelMatrix,
 	public u_ModelViewProjectionMatrix,
 	public u_ColorGlobal_Uint,
-	public u_FogDistanceVector,
+	public u_ViewOrigin,
+	public u_FogDensity,
 	public u_FogDepthVector,
 	public u_FogEyeT,
 	public GLDeformStage {

src/engine/renderer/glsl_source/fogQuake3_fp.glsl

@@ -28,7 +28,8 @@ uniform sampler2D u_FogMap;
 
 uniform float u_FogEyeT;
 
-IN(smooth) vec2		var_TexCoords;
+IN(smooth) float var_FogPlaneDistance;
+IN(smooth) vec3 var_ScaledViewerOffset;
 IN(smooth) vec4		var_Color;
 
 DECLARE_OUTPUT(vec4)
@@ -37,17 +38,21 @@ void	main()
 {
 	#insert material_fp
 
-	float t = step( 0, var_TexCoords.t );
+	float s = length(var_ScaledViewerOffset);
+
+	s += 1.0 / 512.0;
+
+	float t = step( 0, var_FogPlaneDistance );
 
 	if ( u_FogEyeT < 0 ) // eye outside fog
 	{
 		// fraction of the viewer-to-vertex ray which is inside fog
-		t *= var_TexCoords.t / ( max( 0, var_TexCoords.t ) - u_FogEyeT );
+		t *= var_FogPlaneDistance / ( max( 0, var_FogPlaneDistance ) - u_FogEyeT );
 	}
 
 	t = 1.0 / 32.0 + ( 30.0 / 32.0 ) * t;
 
-	vec4 color = texture2D(u_FogMap, vec2(var_TexCoords.s, t));
+	vec4 color = texture2D(u_FogMap, vec2(s, t));
 
 	color *= var_Color;
 

src/engine/renderer/glsl_source/fogQuake3_vp.glsl

@@ -33,13 +33,15 @@ uniform colorPack u_ColorGlobal;
 
 uniform mat4		u_ModelMatrix;
 uniform mat4		u_ModelViewProjectionMatrix;
+uniform vec3 u_ViewOrigin;
 
-uniform vec4		u_FogDistanceVector; // view axis, scaled by fog density
+uniform float u_FogDensity;
 uniform vec4		u_FogDepthVector; // fog plane
 
-// var_TexCoords.s is distance from viewer to vertex dotted with view axis
-// var_TexCoords.t is how far the vertex is under the fog plane
-OUT(smooth) vec2	var_TexCoords;
+// how far the vertex is under the fog plane
+OUT(smooth) float var_FogPlaneDistance;
+
+OUT(smooth) vec3 var_ScaledViewerOffset;
 OUT(smooth) vec4	var_Color;
 
 void DeformVertex( inout vec4 pos,
@@ -74,8 +76,9 @@ void main()
 	position = u_ModelMatrix * position;
 	position.xyz /= position.w;
 
+	var_ScaledViewerOffset = u_FogDensity * (position.xyz - u_ViewOrigin);
+
 	// calculate the length in fog
-	float s = dot(position.xyz, u_FogDistanceVector.xyz) + u_FogDistanceVector.w;
 	float t = dot(position.xyz, u_FogDepthVector.xyz) + u_FogDepthVector.w;
 
 	// HACK: increase cutoff to avoid dark lines at the edge of BSP triangles that stop
@@ -85,7 +88,7 @@ void main()
 		t += 1.5;
 	#endif
 
-	var_TexCoords = vec2(s, t);
+	var_FogPlaneDistance = t;
 
 	var_Color = color;
 }

src/engine/renderer/tr_shade.cpp

@@ -1594,15 +1594,6 @@ void Render_fog( shaderStage_t* pStage )
 	GLIMP_LOGCOMMENT( "--- Render_fog( fogNum = %i, originalBrushNumber = %i ) ---",
 		tess.fogNum, fog->originalBrushNumber );
 
-	// all fogging distance is based on world Z units
-	vec4_t fogDistanceVector;
-	VectorCopy( backEnd.viewParms.orientation.axis[ 0 ], fogDistanceVector );
-	fogDistanceVector[ 3 ] = -DotProduct( fogDistanceVector, backEnd.viewParms.orientation.origin );
-
-	// scale the fog vectors based on the fog's thickness
-	VectorScale( fogDistanceVector, fog->tcScale, fogDistanceVector );
-	fogDistanceVector[3] *= fog->tcScale;
-
 	// rotate the gradient vector for this orientation
 	float eyeT;
 	vec4_t fogDepthVector;
@@ -1618,16 +1609,13 @@ void Render_fog( shaderStage_t* pStage )
 		eyeT = 1; // non-surface fog always has eye inside
 	}
 
-	// see if the viewpoint is outside
-	// this is needed for clipping distance even for constant fog
-	fogDistanceVector[ 3 ] += 1.0 / 512;
-
 	GL_State( pStage->stateBits );
 
 	ProcessShaderFog( pStage );
 	gl_fogQuake3Shader->BindProgram( 0 );
 
-	gl_fogQuake3Shader->SetUniform_FogDistanceVector( fogDistanceVector );
+	gl_fogQuake3Shader->SetUniform_ViewOrigin( backEnd.viewParms.orientation.origin );
+	gl_fogQuake3Shader->SetUniform_FogDensity( fog->tcScale );
 	gl_fogQuake3Shader->SetUniform_FogDepthVector( fogDepthVector );
 	gl_fogQuake3Shader->SetUniform_FogEyeT( eyeT );