CDC类中的m_hDC和m_hArrtriDC有啥区别呢？

[clever101]

CDC类中有两个public数据成员：
HDC m_hDC和 HDC m_hArrtriDC。

请问它们有啥区别呢？

[clever101]

CDC contains two device contexts, m_hDC and m_hAttribDC, which, on creation of a CDC object, refer to the same device. CDC directs all output GDI calls to m_hDC and most attribute GDI calls to m_hAttribDC. (An example of an attribute call is GetTextColor, while SetTextColor is an output call.)

For example, the framework uses these two device contexts to implement a CMetaFileDC object that will send output to a metafile while reading attributes from a physical device. Print preview is implemented in the framework in a similar fashion. You can also use the two device contexts in a similar way in your application-specific code.

There are times when you may need text-metric information from both the m_hDC and m_hAttribDC device contexts. The following pairs of functions provide this capability:
Uses m_hAttribDC Uses m_hDC

GetTextExtent


GetOutputTextExtent

GetTabbedTextExtent


GetOutputTabbedTextExtent

GetTextMetrics


GetOutputTextMetrics

GetCharWidth


GetOutputCharWidth

For more information on CDC, see Device Contexts.