function FXStack( o )
{
	this.apply_fxaa = false;
	this.filter = true;
	this.fx = [];

	this._uniforms = { u_aspect: 1, u_viewport: vec2.create(), u_iviewport: vec2.create(), u_texture: 0, u_depth_texture: 1, u_random: vec2.create() };

	this._passes = null;
	this._must_update_passes = true;

	if(o)
		this.configure(o);
}
FXStack
Helps apply a stack of FXs to a texture with as fewer render calls as possible with low memory footprint
Used by CameraFX and FrameFX but also available for any other use
You can add new FX to the FX pool if you want.
@class FXStack