function init_event()
    local checker_texture = ag.loadTexture("checker.jpg")
    ground = ag.createBox(8, 8, 0.1, {static = true})
    ground:setTexture(checker_texture)
    ag.setCamera(10, -10, 10, 0, 0, 0)
    hilite = ag.createBox(2, 2, 0.1, {static = true})
    hilite:setColor(0.3, 0.5, 1)
    hilite:setPosition(1, 1, 0.1)

    ag.setCursorVisible(true)
end

function mouse_motion_event(x, y, xrel, yrel)
    objects = ag.pickObjects(x, y)
    for i, obj in ipairs(objects) do
        if obj == ground then
            x = obj.pick_pos[1]
            y = obj.pick_pos[2]
            xp = 2 * math.floor(x / 2) + 1
            yp = 2 * math.floor(y / 2) + 1
            if xp >= -3 and xp <= 3 and yp >= -3 and yp <= 3 then
                hilite:setPosition(xp, yp, 0.1)
            end
        end
    end
end