quartz属于core graphic framework的一部分.
为什么都说quartz的坐标系都在左下角呢?因为那是在mac x os里面,如果在iPhone OS中,坐标系是左上角的.
Note: If you are using Quartz 2D for an iPhone application, make sure you understand the native coordinate system of iPhone OS. Its origin is located at the upper left. For more details, see “Drawing to a Graphics Context in iPhone OS.