Don't draw global fog twice

The global fog (used by ET maps) was being drawn twice for opaque
surfaces: once with the fogGlobal shader, and again with the fogQuake3
shader. Don't do that. Besides being redundant, the fogQuake3 shader
doesn't seem to render it correctly (some parts are randomly more
shaded than others).

Author: slipher

src/engine/renderer/tr_main.cpp

@@ -1723,7 +1723,11 @@ void R_AddDrawSurf( surfaceType_t *surface, shader_t *shader, int lightmapNum, i
 		R_AddDrawSurf( surface, shader->depthShader, 0, 0, bspSurface );
 	}
 
-	if( !shader->noFog && fogNum >= 1 ) {
+	// don't draw the global fog twice on opaque surfaces
+	// allow global fog with the fogLE shader although drawing the global fog with the
+	// volumetric (fogQuake3) shader looks kind of buggy
+	if ( !shader->noFog && fogNum >= 1 &&
+		  ( fogNum != tr.world->globalFog || shader->fogPass == fogPass_t::FP_LE ) ) {
 		R_AddDrawSurf( surface, shader->fogShader, 0, fogNum, bspSurface );
 	}
 }