Creating a speedometer

One of the really simple and cool things you can do on the client is draw a speedometer. In this first test, we'll print the raw velocity vector to the screen. Vehicle:GetLinearVelocity returns a Vector3, and we want to turn it into a string, so we can use the tostring function.

function DrawSpeedometer()
	local vehicle = LocalPlayer:GetVehicle()
	-- If vehicle is nil, we're not in a vehicle.
	if vehicle then
		local velocity = vehicle:GetLinearVelocity()
		Render:DrawText(Render.Size / 2, tostring(velocity), Color(255, 255, 255))
	end
end

Events:Subscribe("Render", DrawSpeedometer)

The primary problem with this is that it prints our velocity relative to the world; X is always east, but we want it to be relative to our vehicle. We need to rotate the velocity vector by the vehicle's (inverse) angle:

local velocity = -vehicle:GetAngle() * vehicle:GetLinearVelocity()
Render:DrawText(Render.Size / 2, tostring(velocity), Color(255, 255, 255))

If you play around with this change, you will notice that Z matches your negative forward velocity. This is what we want:

local velocity = -vehicle:GetAngle() * vehicle:GetLinearVelocity()
local forwardVelocity = -velocity.z
Render:DrawText(Render.Size / 2, tostring(forwardVelocity), Color(255, 255, 255))

We can use string.format to make it look better:

local velocity = -vehicle:GetAngle() * vehicle:GetLinearVelocity()
local forwardVelocity = -velocity.z
local speedString = string.format("%i", forwardVelocity * 3.6).." km/h"
Render:DrawText(Render.Size / 2, speedString, Color(255, 255, 255))

We are going to position the text at the bottom and make it larger. This is the final product:

function DrawSpeedometer()
	local vehicle = LocalPlayer:GetVehicle()
	if vehicle then
		local velocity = -vehicle:GetAngle() * vehicle:GetLinearVelocity()
		local forwardVelocity = -velocity.z
		local speedString = string.format("%i", forwardVelocity * 3.6).." km/h"
		
		-- Set position to the middle bottom of the screen.
		local position = Vector2(Render.Width/2, Render.Height)
		-- Move up by the text height.
		position.y = position.y - Render:GetTextHeight(speedString, TextSize.Large)
		-- Center the text.
		position.x = position.x - Render:GetTextWidth(speedString, TextSize.Large) / 2
		
		Render:DrawText(position, speedString, Color(255, 255, 255), TextSize.Large)
	end
end

Events:Subscribe("Render", DrawSpeedometer)