PDF Document Parsing describes how to use CGPDFScanner and CGPDFContentStream objects to parse and inspect
CoreGraphics.CGPDFObject import CoreGraphics.CGPDFOperatorTable import CoreGraphics.CGPDFPage import CoreGraphics.CGPDFScanner
CGShading和 CGGradient:用于绘制剃度; CGColor 和 CGColorSpace;用来进行颜色和颜色空间管理; CGFont, 用于绘制文本; CGPDFContentStream、CGPDFScanner