Added covers, cross-fade

resources/shaders/fog_desktop.fragment

@@ -1,5 +1,6 @@
 //precisionmediump float;
 uniform sampler2D Texture;
+uniform float uAlpha;
 varying vec2 texCoord;
 varying float fogDistance;
 
@@ -14,5 +15,5 @@ void main()
 	float fogFactor = clamp((fogDistance - 30.0) / 10.0, 0.0, 1.0);
 	vec3 finalColor = mix(color.rgb, fogColor, fogFactor);
 
-	gl_FragColor = vec4(finalColor, color.a);
+	gl_FragColor = vec4(finalColor, color.a * uAlpha);
 }