[nvda] Re: NVDA and video hooks

  • From: "Jimmy!" <dosdeoros64@xxxxxxxx>
  • To: <nvda@xxxxxxxxxxxxx>
  • Date: Fri, 20 Feb 2009 19:23:58 -0500

What does JAWS use? (video interception or display hooks)

Which of the two can be ran without installing itself in the operative system?

Thanks in advance,


  ----- Original Message ----- 
  From: James Teh 
  To: nvda@xxxxxxxxxxxxx 
  Sent: Friday, February 20, 2009 6:33 PM
  Subject: [nvda] Re: NVDA and video hooks

  On 21/02/2009 9:21 AM, Derek Roberts wrote:
  > What is the difference between display hooking and vidio intercepting?
  It's pretty technical. Basically, a video intercept works at the driver 
  level. It sits just above the video driver, intercepting text before it 
  is written to the video driver. Display hooking is where the screen 
  reader injects its code into each running application on your system. 
  When most applications need to write to the display, they use a set of 
  functions called GDI functions. The screen reader's code hacks the 
  application so that it runs code from the screen reader instead of the 
  real GDI functions. The screen reader then does its thing and passes the 
  call on to the real GDI function.

  Does this make any sense?

  James Teh
  Email/MSN Messenger/Jabber: jamie@xxxxxxxxxxx
  Web site: http://www.jantrid.net/
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