"Quartz 2D Programming Guide" [graphics context] the role of graphics context, classification, state maintenance, restoration, matrix operation of the context (modify the deformation of the context)

introduction

• The Graphics Context: The data type is CGContextRef

You can think of a graphics context as a drawing destination. A graphics context encapsulates all of the information needed to draw to an underlying canvas,including the current drawing attributes and a device-specific representation of the digital paint on the