Detecting if a point is within a gui frame

[MarpMorp (Marps)]

local oldX = mouse.X
	local oldY = mouse.Y
	
	frame.Position = UDim2.new(0, oldX, 0, oldY)
	
	while state == true do
		heartbeat:Wait()
		frame.Size = UDim2.new(0, mouse.X - oldX, 0, mouse.Y - oldY)
		
		local topLeft = frame.AbsolutePosition
		local bottomRight = topLeft + frame.AbsoluteSize
		
		print(topLeft)
		print(frame.Position)
		print(bottomRight)
		
		for i = 1, #selectable do
			local vector = camera:WorldToScreenPoint(selectable[i].Position)
			print(vector.X, vector.Y)
			if (topLeft.X < vector.X and vector.X < bottomRight.X) and (topLeft.Y < vector.Y and vector.Y < bottomRight.Y) then
				selectable[i].SelectionBox.Visible = true
			end
		end
	end

The problem should be clear, it only selects the part when both the X and Y sizes are positive. I understand why it doesn’t work, I just don’t know how to fix it.

[MarpMorp (Marps)]

I did it but I had to do it in the worst way possible

mouse.Button1Down:Connect(function()
	state = true
	for _, part in ipairs(folder:GetChildren()) do
		if part:IsA("Part") then
			table.insert(selectable, part)
		end
	end
	
	local gui = selectiongui:Clone()
	gui.Name = ("SelectionGui")
	gui.Parent = guifolder
	local frame = gui:WaitForChild("Frame")
	
	local oldX = mouse.X
	local oldY = mouse.Y
	
	frame.Position = UDim2.new(0, oldX, 0, oldY)
	
	while state == true do
		heartbeat:Wait()
		frame.Size = UDim2.new(0, mouse.X - oldX, 0, mouse.Y - oldY)
		
		local topleftX
		local topleftY
		local bottomrightX
		local bottomrightY
		
		local sizeX = frame.Size.X.Offset
		local sizeY = frame.Size.Y.Offset
		local posX = frame.Position.X.Offset
		local posY = frame.Position.Y.Offset
		
		if sizeX ~= 0 or sizeY ~= 0 then
			if sizeX > 0 then
				if sizeY > 0 then
					topleftX = posX
					topleftY = posY
					
					bottomrightX = posX + sizeX
					bottomrightY = posY + sizeY
				else
					topleftX = posX
					topleftY = posY + sizeY
					
					bottomrightX = posX + sizeX
					bottomrightY = posY
				end
			else
				if sizeY > 0 then
					topleftX = posX + sizeX
					topleftY = posY
					
					bottomrightX = posX
					bottomrightY = posY + sizeY
				else
					topleftX = posX + sizeX
					topleftY = posY + sizeY
					
					bottomrightX = posX
					bottomrightY = posY
				end
			end
		else
			topleftX = 0
			topleftY = 0
			bottomrightX = 0
			bottomrightY = 0
		end
		
		for i = 1, #selectable do
			local vector = camera:WorldToScreenPoint(selectable[i].Position)
			print(vector.X, vector.Y)
			if (topleftX < vector.X and vector.X < bottomrightX) and (topleftY < vector.Y and vector.Y < bottomrightY) then
				selectable[i].SelectionBox.Visible = true
			end
		end
	end
	workspace.Folder.Part.SelectionBox.Visible = false
	gui:Destroy()
	print(selectable)
	selectable = {}
end)