Object creation

local objects = {}

function spawn(cmd, id)
    id = tonumber(id) or 931

    local obj = createObject(id, localPlayer.matrix.position + localPlayer.matrix.forward * 2 + localPlayer.matrix.up * 1)

    if (not obj) then
        return
    end

    local minX, minY, minZ, maxX, maxY, maxZ = obj:getBoundingBox()
    local objMatrix = obj:getMatrix()
    local frontSide = objMatrix:transformPosition(Vector3((minX+maxX)/2, minY, minZ))
    local backSide = objMatrix:transformPosition(Vector3((minX+maxX)/2, maxY, minZ))

    local backSideGround = Vector3(backSide.x, backSide.y, getGroundPosition(backSide.x, backSide.y, backSide.z))
    local frontSideGround = Vector3(frontSide.x, frontSide.y, getGroundPosition(frontSide.x, frontSide.y, frontSide.z))

    if (backSideGround.z == frontSideGround.z) then
        return
    end

    local orientation = (frontSideGround.z >= backSideGround.z)
    local neutralPosition = orientation and Vector3(backSideGround.x, backSideGround.y, frontSideGround.z) or Vector3(frontSideGround.x, frontSideGround.y, backSideGround.z)

    objects[#objects+1] = {
        object = obj,
        orientation = orientation,
        sides = {
            front = frontSide,
            back = backSide
        },
        ground = {
            front = frontSideGround,
            back = backSideGround,
            neutral = neutralPosition
        }
    }

    local angle = getAngle(frontSideGround, backSideGround, neutralPosition)
    local degAngle = math.deg(angle) + (orientation and -90 or 0)
    local rotx, roty, rotz = getElementRotation(obj)

    print("back/front angle", orientation, rotx, angle, degAngle)
    setElementRotation(obj, degAngle, roty, rotz)
end
addCommandHandler("spawn", spawn)

function clear()
    for _, container in ipairs(objects) do
        destroyElement(container.object)
    end
    objects = {}
end
addCommandHandler("clear", clear)

function render()
    for _, container in ipairs(objects) do
        local front, back = container.sides.front, container.sides.back
        dxDrawLine3D(front.x, front.y, front.z, back.x, back.y, back.z, tocolor(255, 0, 0), 2)

        front, back, neutral = container.ground.front, container.ground.back, container.ground.neutral
        dxDrawLine3D(front.x, front.y, front.z, back.x, back.y, back.z, tocolor(0, 255, 0), 3)

        if (container.orientation) then
            dxDrawLine3D(front.x, front.y, front.z + 0.01, neutral.x, neutral.y, neutral.z + 0.01, tocolor(0, 0, 255), 3)
        else
            dxDrawLine3D(back.x, back.y, back.z + 0.01, neutral.x, neutral.y, neutral.z + 0.01, tocolor(0, 0, 255), 3)
        end
    end
end
addEventHandler("onClientRender", root, render)

function distance(vec1, vec2)
    return math.sqrt(
        (vec1.x - vec2.x) ^ 2 +
        (vec1.y - vec2.y) ^ 2 +
        (vec1.z - vec2.z) ^ 2
    )
end

function getAngle(vec1, vec2, vec3)
    local ab = distance(vec1, vec2)
    local bc = distance(vec2, vec3)
    local ac = distance(vec1, vec3)

    return math.acos(
        ((ab ^ 2) + (bc ^ 2) - (ac ^ 2)) / (2 * ab * bc)
    )
end