Intercept the rendering and interaction of the desktop - c#

Is it possible, without modifying the Windows OS, to have a piece of software intercept the rendering of the desktop, and modify it before it is displayed? For example, if I wanted to intercept it, and apply a fish-eye effect to my entire screen, would this be possible?
If so, how would I go about doing so? (Don't worry about the effects, was only an example, i merely need the interception side of things)
Also, I need to be able to intercept mouse clicks, and modify their position before Windows responds to the input.
If anyone has links to this, or similar projects in C# or C++, that would also be extremely helpful.

Yes it's possible. E.g. the WinAmp player does that. However that code is very unstable so be prepared to reboot if you try it.

Related

Writing a program to stop another program from taking screenshots [duplicate]

i need to block any screen capture software on the computer from taking screen shots. Since all of them are work on standard API-functions, i think i could monitor and block them.
I need to use C#.
All i have found is how to monitor and block them in a certain program (screen capture program). They are looking for a function in the program, then they change it address on mine function address.
But how can i do it, if i haven't any certain programs? I need to block anyone which tries to take a screenshot.
If your final goal is possible or not I don't know, but for the hooking the API portion I can help you out.
I have used the library EasyHook many times in the past, this will let you hook and intercept system function calls from C# code fairly easily. Just read through the PDF tutorial for setup instructions.
For actually finding the API's I recommend Rohitab's API Monitor, it's still in Alpha stages but it works really well and is free. You just hook it on to a processes and it tells you every external DLL call it makes (with the parameters it passed if you have the xml definition file for the DLL, the program comes with almost all of the windows API dll's pre-defined).
The combination of EasyHook and API Monitor is a great 1-2 punch for mucking with other program's calls.
It is not possible to prevent screenshots from being taken. The battle is already lost because of the DWM (Desktop Window Manager). It's lower level than Win32 and device contexts.
If you want to protect the text in your program, there are a lot easier ways to extract it than doing screenshots and OCR. TextOut and/or Direct2D hooking and accessibility APIs.
If there's a lot of IP in your program. Then don't make it all available onscreen. Make sure it's tedious to crawl the GUI for text, and hard to automate it. And don't load whole texts in memory of the program.
Possible solutions:
1. To prevent copying of text. Draw the text as an image.
2. To prevent accessibility technologies, like screen readers - override WndProc in your control, handle and ignore the window message WM_GETOBJECT.
3. To make it harder if they try to use OCR. Draw graphics behind the text. Human readable, but much harder for a machine to interpret it.
Neither of these methods are invasive for the user.
** A very invasive suggestion **:
If you are really serious about preventing anyone from "stealing" your content.
Implement mouse and keyboard hooks. Filter out typical copy shortcuts. Prevent the mouse from leaving the boundaries of your application.
Allow your application to only run when the OS runs well-known processes and services.
If any process starts which you don't recognize, black out the application and notify the user about it, and request the user to close it. And ofc make sure someone is not just spoofing a well-known process.
Monitor the clipboard as you suggested yourself.
You can ofc soften some of these suggestions based on the context of your application.
As Scott just posted it likely can be prevented with API hooks to see that paint events only go to desktop bound handles and not others, and refuse to paint otherwise. However, you need to consider the following scenarios and see if they're relevant threat to your approach or not:
Your software may be running in a virtual machine like VMWare. Such software has capapbilities to capture screen that does so at "virtual hardware" level, and your API hooks will not be able to discern it - and this would be the easiest way approach if I wanted to bypass your protections.
As a post suggests here, nothing also prevents someone to take monitor cable and plug it into another computer's capture card, and take screenshot that way. Again, your hooks will be helpless here.
Bottom line, you can make it somewhat harder to do, but bypassing such protection may be pretty trivial thing to do.
My 2c.

Get caret position in non-GDI apps

So I'm writing an accesibility app that needs to know the location of the text entry caret. I tried GUIThreadInfo, but while that works in basic apps like Notepad, it fails in more complex ones like Chrome, iTunes, etc. that handle their own UI.
Is there even a way to get the caret position from apps like this?
Yes, doesn't work. The caret is an implementation detail of user32, associated with a window. Applications like browsers don't use window controls, far too expensive. And they don't have to, there's a separate API to allow such programs to provide an interface to accessibility apps like screen readers. Start reading here. Not easy to use from a C# app, this project can lessen the pain. No endorsement, never actually used it myself.

How can I know if the user has made a screenshot?

I'm writing a small c# program, I don't want the final user to take screenshots while using my program, is it possible? Or even if he takes one, how can I know it?
Thanks in advance and sorry if this is a poor-content question due to my lack of experience in c# coding.
You can create a system-wide keyboard hook using the low-level keyboard filter and cancel any printscreen keyboard combination. But if someone has also installed a helper application (like Gadwin or something) it'll become a lot more difficult because you won't know beforehand what keyboard shortcut you should catch (most tools allow to specify your own hooks).
Here's an article on using hooks in C#
and here's a ready-made keyboard hook library for .net that uses global mouse and keyboard hooks (use Google to find more freeware and commercial libraries and tools).
On a side note: it's generally not preferred to change the system behavior. Screenshots are system behavior and serve a distinguished purpose for trouble shooting. If you prevent this, users will not be able to show you a screenshot of something wrong. But if you must do it, you can do it.
EDIT: on a deeper level, you can install an API hook. All screenshot applications use API calls to get the content of a (part of) the screen. But API hooks are hard to get right. A more trivial way is probably by writing a user-level driver. While you can prevent all this, it is really worth all the trouble?
You might want a keyboard hook. But it'll tell you if the user pressed the "print screen" key, not if someone programmatically take a screenshot using some GDI function.
I doubt it's possible to prevent all the ways of taking a screenshot.
General answer: No. It's not possible to detect this - especially from C#. There are dozens of ways to take screenshot and even applications written in C++/WinAPI can only detect some of them, but not all.
Also consider - what if user is running your app in virtual machine? He'll be able to take screenshots at host machine and you can do absolutely nothing to detect (not even prevent) this.

Make entire screen monochrome and other full screen effects

Does anyone know how to apply effects to the entire screen, in c# or any programming language.
I'm mostly interested in making the screen monochrome (specifically green-white instead of black white).
I know a cross-graphic card solution is possible because I found a program that can do it:
http://www.freedomscientific.com/products/lv/magic-bl-product-page.asp
Anyone knows how to accomplish something this or where to look?
Thanks !!
There is no easy Windows API to modify the entire screen contents. But this could be done at the device driver level.
Otherwise you have to resort to some Windows API tricks: place a "fake" window over the entire desktop, in a loop: grab the entire screen contents without grabbing fake window contents, do your processing to get the monochrome effect, then display that on the fake window. Yes, it's hacky and slow, but possible. Even more hacky, when you get mouse clicks to "go through" the fake window (lots of SetWindowsRgn calls).
So cross-platform here means using GDI, though some older DirectDraw APIs might work, in that case, you have a much easier time with hardware overlays (and better performance). Though I'm not sure how many cards actually support hardware overlays, and if newer versions of windows support the older DirectDraw APIs.
One more possibility is if the video card has a C# or C++ or C API, then you can do whatever you want with the card without writing device driver code.
Then there's CUDA, but I haven't yet tried that out. I know it's for stream processing on nVidia boards, but I wonder if it could get you an easy backdoor into the video display stuff.
To help people in the future who are interested in this:
This is possible with the Magnification API's color effect method. This allows one to use a matrix that can be applied to the whole screen.
NegativeScreen is an open source project that implements the feature you are describing in C#.
Unfortunately, this only works with affine transformations, as the API takes only an augmented matrices rather than a delegate or something.

Need help in finding name of specific thing I'm trying to do

I think it's possible to somehow hook with the windows environment (specifically explorer.exe) and trigger specific things, for example launching control panel and using it as if I had mouse (meaning I'm clicking the interface from the code).
Basically what I'm trying to do is automate some redundant tasks I do often, just I don't know how it's done, or even how it's called. Anyone can point me in right direction?
Thanks!
Forget about "automated clicking". GUI tools are just front-ends to control the system. You can control the system like they do, it will be much easier.
Huge possibilities can give you Microsoft Management Console. Each "snap-in" can be accessed via COM model. Some of them have GUI front-ends, find and fire "*.msc" files (somewhere in Windows directory) to try them.
There is many command line tools i.e. "net" command has huge abilities related to networking.
PowerShell may be a better choice instead of C# or C++, it's designed for task automation. You can easily use COM, .NET, MMC ...
Windows Explorer has a COM object model that you can call from both C# and C++. (Most of the examples on MSDN are in Javascript or VBScript, which I guess aren't your languages of choice, but they demonstrate that the API is straightforward to call.)
AutoHotKey is a scripting environment specifically designed for this sort of task
If you want mostly to launch control panel you can do using RunDll32 interface existing in the most control panel applets. See http://www.osattack.com/windows-7/huge-list-of-windows-7-shell-commands/ , http://support.microsoft.com/kb/167012 or http://www.winvistaclub.com/t57.html for example. For the corresponding API see http://support.microsoft.com/kb/164787.
Another option is usage of control.exe (see http://msdn.microsoft.com/en-us/library/cc144191.aspx and http://vlaurie.com/computers2/Articles/control.htm).
If you google more you will find much more examples which you can to automate a lot of things without using of some general ways to automate GUI.
At more or less the lowest level within Win32, you can use the SendMessage() API to send raw click messages to windows of interest. This will rely on a lot of intrusive knowledge about the apps you intend to drive. However, you could easily implement a "click recorder" that could replay click sequences captured from user interaction.

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