ios - Quartz 2D 不透明数据类型

Question

Quartz 2D Opaque Data Types

The Quartz 2D API defines a variety of opaque data types in additionto graphics contexts. Because the API is part of the Core Graphicsframework, the data types and the routines that operate on them usethe CG prefix.

Quartz 2D creates objects from opaque data types that your applicationoperates on to achieve a particular drawing output. Figure 1-3 showsthe sorts of results you can achieve when you apply drawing operationsto three of the objects provided by Quartz 2D. For example:

You can rotate and display a PDF page by creating a PDF page object,applying a rotation operation to the graphics context, and askingQuartz 2D to draw the page to a graphics context.

You can draw apattern by creating a pattern object, defining the shape that makes upthe pattern, and setting up Quartz 2D to use the pattern as paint whenit draws to a graphics context.

You can fill an area with an axial orradial shading by creating a shading object, providing a function thatdetermines the color at each point in the shading, and then askingQuartz 2D to use the shading as a fill color.

我无法理解 apple reference guide 的这一部分

特别是我加粗的东西，比如“他们”指的是什么？

请澄清一般不透明数据类型，而不是 c 或 c++ 术语。

提前致谢，问候。

Answer 1

短语不透明类型 仅表示包含或引用您不应查看甚至无法查看的数据的类型。例如，Quartz 提供了 CGContextRef 类型。提供了使用 CGContextRef 实例创建、获取、操作和释放图形上下文的函数，但您无法查看 CGContextRef 内部并查看其中的内容。如果不使用所提供的功能，您将无法合理地使用或更改上下文。