Inverse of math.tan()

[gucypher]

Hello, I am relatively experienced with lua, but for some reson, I cannot find a way to inverse the math.tan function.

I want to find the relative angle of attack on EntityTakeDAmage to get rid of those ugly trapazoids and replace them with damage indicators around the crosshairs, but to do so, I need the angles relative to the person being inflicted.

function GM:EntityTakeDamage(ent, attacker, inflictor, damage)
	if ent:IsPlayer() then
		local vpos = ent:GetPos()
		local apos = attacker:GetPos()
		local vang = ent:EyeAngles() -- used later to add to the world angle we should find
		local distx = vpos.x - apos.x --adj
		local disty = vpos.y - apos.y -- opp
		local ratio = disty / distx -- this is what we need to plug into the inverse tangent function to get the degrees.
		local raddegree = math.tan(ratio) ^ -1
		raddegree = math.Rad2Deg( raddegree  )
		local dataangle = math.fmod(raddegree, 360)-- simulates arc tangent
		data =  dataangle + vang.yaw
		ent:ChatPrint("Angle of attack = "..data.." deg.")
	end
	--continue with funciton
end

Using trig with lua is a little confusing for me. Is there any alternative?

[Skapocalypse]

math.pale()?

But really, I don't think there is anything.

[Grea$eMonkey]

Check out the math library: [url]http://wiki.garrysmod.com/?title=Math[/url]

[gucypher]

I've searched. I don't think there is a way to do it with any inverse of a trig function. There might be a way though afor loop. It would only have to go up to 360. Anyone have ideas? Thank's in advance.

[MakeR]

tan(a)^-1 (1/tan(a)) is definitely not equal to arctan(a). The ^-1 is just a maths notation that means arctan. I think you are looking for Math.atan2(disty, distx).

[gucypher]

^-1 should be the inverse of the function. and 1/tan(a) is the cot, not the arc tan.
Arc tan is defined at
math.tan(a) +- math.pi() * x where x is the number of times the period is repeated and math.pi() is the general period of an unmodified tan function in radians. That is for graphs, not triangles.

[editline]05:02PM[/editline]

local vpos = ent:GetPos()
local apos = attacker:GetPos()
local vang = ent:EyeAngles() -- used later to add to the world angle we should find
local distx = vpos.x - apos.x --adj
local disty = vpos.y - apos.y -- opp
local test = math.atan2(disty, distx)
test = math.Rad2Deg( test ) -- the angle from the origin(world)
data =  test + vang.yaw --make it relative to the player.
ent:ChatPrint("Angle of attack = "..data.." deg.")

[CowThing]

[url=http://wiki.garrysmod.com/?title=Math.atan]math.atan()[/url]?

[MakeR]

tan(a)^-1 == cot(a) != atan(a)

[gucypher]

Yes. Arc tangent is much different than cot.

This seems to be working better.

local vpos = ent:GetPos()
local apos = attacker:GetPos()
local eyeang = ent:EyeAngles()
local eyaw = eyeang.y
if eyaw > 0 then
	bearing = 360 - eyaw
else
	bearing = math.abs(eyaw)
end
local distx = vpos.x - apos.x --adj
local disty = vpos.y - apos.y -- opp
local test = math.atan2(disty, distx)
test = math.Rad2Deg( test ) -- the angle from the origin(world)
data =  test + bearing --make it relative to the player.
data = data - 180 -- for some reason, it's rotated 180 deg.
ent:ChatPrint("Angle of attack = "..math.abs(data).." deg.")

[Entoros]

If you didn't need to get the angle of attack, you could just do it easily like this:

[lua]
local pos = attacker:GetPos():ToScreen()
if pos.x > ScrW() then

// Draw stuff to the right

elseif pos.x < 0 then

// Draw stuff to the left

end[/lua]

[gucypher]

Well, I'm converting this angle to a basig 0- 360 deg angle used todraw and fade a textured damage indicator in the HUD. I alreadu have a tadial compass, so i will also use the degrees to add warnings on the compass.

[Lt_Captain]

Are we talking functional inverse or multiplicative inverse?

tan(x):

Functional inverse is atan(x) (or tan-1(x) which in most calculators LOOKS like the multiplicative inverse but it really denotes the functional inverse). And the multiplicative inverse is cos(x) / sin(x)

[gucypher]

functional inverse.