Fixed fog in legacy 3D engine. Now computed same as new engine, with 4-bit light modifier and corrected fog mixing in shaders.

Src/Graphics/Legacy3D/Models.cpp

@@ -686,10 +686,8 @@ void CLegacy3D::InsertVertex(ModelCache *Cache, const Vertex *V, const Poly *P,
   if ((P->header[6]&0x00800000))  // if set, polygon is opaque
     translucence = 1.0f;
     
-  // Fog intensity (for luminous polygons)
-  GLfloat fogIntensity = (GLfloat) ((P->header[6]>>11)&0x1F) * (1.0f/31.0f);
-  if (!(P->header[6]&0x00010000)) // if not luminous, always use full fog intensity
-    fogIntensity = 1.0f;
+  // Fog intensity (apparently used for both luminous and shaded polygons)
+  GLfloat fogIntensity = (GLfloat) ((P->header[6]>>11)&0x1F) * (1.0f/15.0f);  // only 4 bits seem to actually be used?
 
   /*
    * Contour processing. Any alpha value sufficiently close to 0 seems to

Src/Graphics/Legacy3D/Shaders/Fragment.glsl

@@ -186,8 +186,8 @@ void main(void)
 	// Translucency (modulates existing alpha channel for RGBA4 texels)
 	fragColor.a *= fsTransLevel;
 
-	// Apply fog under the control of fog factor setting from polygon header
-	fragColor.rgb = mix(gl_Fog.color.rgb, fragColor.rgb, fsFogFactor);
+	// Apply fog
+	fragColor.rgb = mix(fragColor.rgb, gl_Fog.color.rgb, fsFogFactor);
 
 	// Store final color
 	gl_FragColor = fragColor;

Src/Graphics/Legacy3D/Shaders/Fragment_MultiSheet.glsl

@@ -46,7 +46,7 @@ uniform float		mapSize;			// texture map size (2048,4096,6144 etc)
 // Inputs from vertex shader 
 varying vec4		fsSubTexture;	// .x=texture X, .y=texture Y, .z=texture width, .w=texture height (all in texels)
 varying vec4		fsTexParams;	// .x=texture enable (if 1, else 0), .y=use transparency (if > 0), .z=U wrap mode (1=mirror, 0=repeat), .w=V wrap mode
-varying float		fsTexFormat;	// T1RGB5 contour texture (if > 0)
+varying float		fsTexFormat;	// T1RGB5 contour texture (if > 0)
 varying float		fsTexMap;		// texture map number
 varying float		fsTransLevel;	// translucence level, 0.0 (transparent) to 1.0 (opaque)
 varying vec3		fsLightIntensity;	// lighting intensity 
@@ -231,8 +231,8 @@ void main(void)
 	// Translucency (modulates existing alpha channel for RGBA4 texels)
 	fragColor.a *= fsTransLevel;
 
-	// Apply fog under the control of fog factor setting from polygon header
-	fragColor.rgb = mix(gl_Fog.color.rgb, fragColor.rgb, fsFogFactor);
+	// Apply fog
+	fragColor.rgb = mix(fragColor.rgb, gl_Fog.color.rgb, fsFogFactor);
 
 	// Store final color
 	gl_FragColor = fragColor;

Src/Graphics/Legacy3D/Shaders/Vertex.glsl

@@ -194,7 +194,7 @@ void main(void)
 	
 	// Fog
 	float z = length(viewVertex);
-	fsFogFactor = clamp(1.0-fogIntensity*(gl_Fog.start+z*gl_Fog.density), 0.0, 1.0);
+	fsFogFactor = fogIntensity*clamp(gl_Fog.start+z*gl_Fog.density, 0.0, 1.0);
 
 	// Pass viewspace Z coordinate (for spotlight)
 	fsViewZ = -viewVertex.z;	// convert Z from GL->Real3D convention (want +Z to be further into screen)

Src/Graphics/Legacy3D/Shaders3D.h

@@ -229,7 +229,7 @@ static const char vertexShaderSource[] =
 "  \n"
 "  // Fog\n"
 "  float z = length(viewVertex);\n"
-"  fsFogFactor = clamp(1.0-fogIntensity*(gl_Fog.start+z*gl_Fog.density), 0.0, 1.0);\n"
+"  fsFogFactor = fogIntensity*clamp(gl_Fog.start+z*gl_Fog.density, 0.0, 1.0);\n"
 "\n"
 "  // Pass viewspace Z coordinate (for spotlight)\n"
 "  fsViewZ = -viewVertex.z;  // convert Z from GL->Real3D convention (want +Z to be further into screen)\n"
@@ -436,8 +436,8 @@ static const char fragmentShaderSingleSheetSource[] =
 "  // Translucency (modulates existing alpha channel for RGBA4 texels)\n"
 "  fragColor.a *= fsTransLevel;\n"
 "\n"
-"  // Apply fog under the control of fog factor setting from polygon header\n"
-"  fragColor.rgb = mix(gl_Fog.color.rgb, fragColor.rgb, fsFogFactor);\n"
+"  // Apply fog\n"
+"  fragColor.rgb = mix(fragColor.rgb, gl_Fog.color.rgb, fsFogFactor);\n"
 "\n"
 "  // Store final color\n"
 "  gl_FragColor = fragColor;\n"
@@ -681,8 +681,8 @@ static const char fragmentShaderMultiSheetSource[] =
 "  // Translucency (modulates existing alpha channel for RGBA4 texels)\n"
 "  fragColor.a *= fsTransLevel;\n"
 "\n"
-"  // Apply fog under the control of fog factor setting from polygon header\n"
-"  fragColor.rgb = mix(gl_Fog.color.rgb, fragColor.rgb, fsFogFactor);\n"
+"  // Apply fog\n"
+"  fragColor.rgb = mix(fragColor.rgb, gl_Fog.color.rgb, fsFogFactor);\n"
 "\n"
 "  // Store final color\n"
 "  gl_FragColor = fragColor;\n"