Lua: check for object above water

[OtherChen]

I'm trying to make something hover close to the ground/water without touching it. Ground is easy: (thing.z - thing.floorz). For water, (thing.z - thing.watertop) doesn't work unless the object is underwater, so I'm spawning a "sinker" dummy mobj on the floor under the object and checking its properties. I've tried the following methods:

• Reading the sinker's eflags doesn't work, as (sinker.eflags & MFE_UNDERWATER) always returns false.
• Reading the sinker's watertop always gives INT32_MAX, so (sinker.watertop > sinker.z) always returns true.
• Using different mobj types for the dummy: thok trails, water splishes, fire, rings, red rings, and crawlas. I left the sprites showing and the objects are clearly underwater.
• Changing the dummy's scale and height to various values, including FRACUNIT, 1, and 0.
• Waiting a few tics and checking the underwater-ness of dummy mobjs from a few tics ago gives the same result

This shouldn't be so difficult. What am I missing? Is there a parallel to mobj.watertop that checks for water below an object rather than the surface above the object?

 

[toaster]

Does the sinker have MF_NOTHINK? If so, that's your problem. Internal mechanisms such as mo.eflags and mo.watertop are only set if there's a thinker running to do stuff. You might be able to get away with MF_SCENERY (which is a reduced, less intensive thinker) if all you want is mo.eflags, but I'm not sure where mo.watertop is handled.

 

[OtherChen]

I tried using objects that I knew had thinkers, like rings and crawlas. Still no luck (unless filling GFZ1 with rings and crawlas has some artistic merit behind it).

 

[toaster]

Rings have just MF_SCENERY iirc, and don't update anything after spawn. Crawlas definitely have thinkers, though, which confuses me. Have you tried defining your own freeslot MT_SINKER object?

Can't help that much because I'm spending today travelling, but.

 

[Monster Iestyn]

Does the "sinker" object have any health at all? IIRC objects with no health don't check for water (and thus don't set any properties to do with water).

 

[OtherChen]

Solved it; the sinker mobj needs to persist for a few tics while checking its flags. Or something.

local function GetHoverZ(thing)
	-- Get the floor or water height under a hovering object
	-- (lags behind by 1 tic)
	local HOVERZ = thing.floorz
	if thing.sinkerhelper and thing.sinkerhelper.valid then
		if thing.sinkerhelper.eflags & MFE_UNDERWATER then
			HOVERZ = thing.sinkerhelper.watertop
		end
	end
	thing.sinkerhelper = P_SpawnMobj(thing.x, thing.y, thing.floorz, MT_MOUSE)
	if thing.sinkerhelper and thing.sinkerhelper.valid then -- Can't be too careful
		thing.sinkerhelper.fuse = 3
		thing.sinkerhelper.flags2 = MF2_DONTDRAW -- remove if thing is MT_MOUSEHOLE
	end
	return HOVERZ
end