How Do ScreenReaders get Text Information from Focused Windows?

Question

Screenreaders access information in other programs via what I suppose is a Windows API. Can anyone comment on how this is done and provide a link to some documentation?

Are there any serious limitations I should be aware of?

If you know anything about how this works in other operating systems that would be of interest as well.

Answer 1

Most screen readers use UI Automation to access information in other programs. Some applications don't provide accessibility information in this way (bad programmers! bad! bad!), so some screen readers use mirror drivers to intercept the low-level drawing operations, and then regenerate the application's information from there. (I don't recommend this; it's painful, prone to hang your system, and not supported in Windows 8 and above. But, if you really have to do it, well, you really have to do it.)

IOS has something similar, although I'm not familiar with it. Useful tags on stack overflow are [ui-automation] and [Microsoft-ui-automation].

Answer 2

屏幕阅读器通常通过Microsoft Active Accessibility和/或UI Automation访问UI 。