This is a helper mod that implements a fly mode that other plugins can hook into and enable/disable. This mod handles the movement and inputs, but not enabling/disabling the fly mode. By itself, this plugin does NOTHING. (other than add 2 settings that are ignored)
First, add a [BepInDependency("Terrain.CommonFly")] annotation to your plugin.
CommonFly.flying property to true/false.CommonFly.noclip property, which prevents the fly mode from suddenly ending when you hit solid objects. Specifically, it completely disables your player collider client-side.Both of these are auto properties instead of fields for your patching convenience, because then you can use something like [HarmonyPatch(typeof(CommonFly), nameof(CommonFly.flying), MethodType.Getter)] if you need to change the value when it's used (which is like 3-4 times every physics frame or something actually).
The other two properties CommonFly.flyUp and CommonFly.flyDown are the actual inputs sent by the player. You probably shouldn't mess with their setters, but you can Reverse Patch them if you really want to anyways.
Icon made by Shocho. I haven't modified the icon outside of the preview options The Noun Project provides.