How to do wall/ceiling detection?

Questions
#1

So far my little test game has gone well, and the floor detection is okay, but I’m trying to figure out how to detect ceilings / roofs and move the opposite direction. Is there a way I could detect like, the specific side of a collision object I’m detecting? (btw kinematic)

Code for my movement:

function init(self)
	msg.post(".", "acquire_input_focus")
	self.startPos = vmath.vector3(640, 360, 0)
	go.set_position(self.startPos)
	self.i = vmath.vector3()
	self.VelocityY = -1
	self.jumpLimit = 1
	fall = true
	jumping = 0
end

function on_message(self, message_id, message, sender)
	if message_id == hash("contact_point_response") then
		self.p = go.get_position()
		self.p.y = self.p.y + (math.abs(self.VelocityY) * 1.25)
		if jumping > 0 then
			self.VelocityY = self.VelocityY + 5
			self.VelocityY = self.VelocityY * -1
		else
			self.VelocityY = .25
		end
		jumping = 0
	end	
end

function update(self, dt)
	self.p = go.get_position()
	self.p = self.p + self.i
	self.p.y = self.p.y + self.VelocityY
	if fall == true then
		if self.VelocityY > -48 then
			self.VelocityY = self.VelocityY - .5
		end
	end
	go.set_position(self.p)
	self.i = vmath.vector3()
end


function on_input(self, action_id, action)
	if action_id == hash("up") then
		if action.pressed and jumping < self.jumpLimit then
			self.VelocityY = 15
			jumping = jumping + 1
		end
	elseif action_id == hash("left") then
		self.i.x = -5
	elseif action_id == hash("right") then
		self.i.x = 5
	end
end
#2

The contact point response message reports the position of the two objects colliding. From this you can infer which side of a wall you’re colliding with.

1 Like
#3

You can also use the collision normal. If it points down it’s a collision with something above you and if it points left or right it is a wall.