VBO-related optimizations and improvements (#14395)

client/shaders/cloud_shader/opengl_fragment.glsl

@@ -0,0 +1,17 @@
+uniform vec4 fogColor;
+uniform float fogDistance;
+uniform float fogShadingParameter;
+varying vec3 eyeVec;
+
+varying lowp vec4 varColor;
+
+void main(void)
+{
+	vec4 col = varColor;
+
+	float clarity = clamp(fogShadingParameter
+		- fogShadingParameter * length(eyeVec) / fogDistance, 0.0, 1.0);
+	col.rgb = mix(fogColor.rgb, col.rgb, clarity);
+
+	gl_FragColor = col;
+}