I like to make an overlay with the following properties:
- should work at least on Windows 8.1
- should be on top on everything, like a mouse cursor
- should incorporate the pixels which are already on the background, like a blur filter
- no flickering
Details to each of this points:
1) I assume that WDM is activated and DirectX 11.2 is used. Sure it would be nice to have it working on other Windows versions but this has no priority.
2) The problem is that with simply using the WS_EX_TOPMOST, menus from applications are over my overlay. In my case this really hurts as I like to display something with the same properties as a cursor. Imagine that a cursor suddenly is hidden if you open a menu -> unacceptable.
3) I like to read the pixels from the Windows desktop, including any effect Windows applies (like blur), and use this information for my filter. If I add my overlay, as described in 2, I should be able to get a fresh unobstructed copy of the background in the next frame and not read out my own overlay.
4) If I just write something into the Windows desktop directly, it gets overwritten immediately on the next frame by Windows itself. This is not acceptable.
One example of such an application is a magnifying glass, which exactly has all the properties I need. But for this case Windows 8.1 has an API. In contrast I like to write a program which displays a hand on the desktop (which is controlled by Leap Motion) which influences the Windows desktop, so you almost "feel" how you move your hand over the desktop.
If I write a tiny DirectX and/or OpenGL application for myself this is all very easy:
- render all the regular stuff to a texture
- use this texture for a post processing filter and add all my stuff on top of it
- render just a quad to the back buffer
But I like to do that for the whole Windows desktop.
I found many different application, but they are to no use for me:
- application which claim to be on top, are still behind menus. This normally doesn't really hurt, but is unacceptable for a cursor-alike thing
- screen capturing programs which hook them self in all running programs are nice, but I want to hook myself into WDM
- normally screen capturing programs do not draw anything into the back buffer, so they get every frame a new unobstructed back buffer
My questions can be boiled down to: How can I write my own magnifying glass for Windows 8.1.
I fear that my only serious option is to hook myself into WDM, what I try to avoid.
I'm happy to hear any idea how to achieve this, or hints to application which are doing what I describe.
