Paint

local function createLine(startPos, endPos)
    local line = Instance.new("Frame")
   -- line.Size = UDim2.new(0, (endPos - startPos).Magnitude, 0, 2)
line.Size = UDim2.new(0, 5, 0, 2)
    line.Position = UDim2.new(0, startPos.X, 0, startPos.Y)
    line.AnchorPoint = Vector2.new(0, 0.5)
    line.Rotation = math.deg(math.atan2(endPos.Y - startPos.Y, endPos.X - startPos.X))
    line.BackgroundColor3 = Color3.new(1, 0, 0)
    line.BorderSizePixel = 0
    line.Parent = Canvas
end

local function getRelativePosition(input)
    local absolutePosition = Canvas.AbsolutePosition
    local relativePosition = Vector2.new(input.Position.X - absolutePosition.X, input.Position.Y - absolutePosition.Y)
    return relativePosition
end

UserInputService.InputBegan:Connect(function(input)
    if input.UserInputType == Enum.UserInputType.MouseButton1 or input.UserInputType == Enum.UserInputType.Touch then
        drawing = true
        lastPosition = getRelativePosition(input)
    end
end)

UserInputService.InputEnded:Connect(function(input)
    if input.UserInputType == Enum.UserInputType.MouseButton1 or input.UserInputType == Enum.UserInputType.Touch then
        drawing = false
        lastPosition = nil
    end
end)

UserInputService.InputChanged:Connect(function(input)
    if drawing and (input.UserInputType == Enum.UserInputType.MouseMovement or input.UserInputType == Enum.UserInputType.Touch) then
        local currentPosition = getRelativePosition(input)
        if lastPosition then
            createLine(lastPosition, currentPosition)
        end
        lastPosition = currentPosition
    end
end)