Prevent running Windows 10 OCR if screen curtain is enabled.

[CyrilleB79]

Link to issue number:

Fixes #11911

Summary of the issue:

User are not informed that OCR cannot be achieved when the screen curtain is enabled. They may then think that Windows 10 OCR is a non-working / broken feature.

Description of how this pull request fixes the issue:

• Do not perform OCR if screen curtain is active. Instead, issue a message to inform the user that he needs to disable the screen curtain to perform OCR.
• Add some information in the user guide (screen curtain section and OCR section) to document this incompatibility.
• Also document some other related limitations:
  • screenshots cannot be taken if OCR is active
  • other visual aids may cause incorrect results in recognition. I did not mention explicitly them.

For reference, even if I did not include these details in the guide, here is the status of incompatibility between OCR and visual aids:

• screen curtain: fully incompatible
• Windows Magnifier: partially incompatible: the OCRed object need to be fully visible on the screen to have a correct result
• Visual Highlight (ex: Focus Highlight): incompatible in some rare cases, e.g. when the browse mode cursor highlighter ioverlaps the OCRed zone
• Zoomtext remains fully compatible with OCR even if the OCRed zone is not in the zoomed view

Testing performed:

• Tested that OCR command (NVDA+R) still works if screen curtain is disabled
• Tested that no OCR is performed and that the warning message is heard when trying to OCR when screen curtain is enabled. The 3 way to enable screen curtain have been tested:
• temporary activation via shortcut
• full activation via shortcut
• activation from the vision setting window (before pressing OK or cancel)

Known issues with pull request:

This PR is limited to warn and document the incompatibility between OCR and screen curtain. It does not offer a solution.
The goal is to have this PR merged quite quickly so that people using screen curtain do not think erronously that OCR is just a broken feature.

Change log entry:

Section: Bug fixes
NVDA now prevents to perform Windows 10 OCR if screen curtain is enabled. (#11911)

[CyrilleB79]

This PR is ready to review.

Since the original issue may let some think that OCR feature does not work and since the modification is quite small, I am wondering if this could still be integrated in 2020.4.

I know there is another issue regarding the doc organization concerning the OCR (#11861. However, I expect the current PR to be integrated quite quickly if possible (2020.4 or 2021.1); on the contrary, I expect #11861 to generate more comments and discussion regarding the doc organization, not only regarding OCR.

Cc @Qchristensen for the doc review, @feerrenrut for the rest and the question about integration in 2020.4.

[AppVeyorBot]

• System test failure
• Build (for testing PR)

See test results for failed build of commit 96b1f0db15