How to draw graphics/text on top of another application

Question

I want to enhance an application, but there is no 3:e party API available. So basically the idea is to draw graphics/text on top of the applications windows.

There are problems with z order, clipping, and directing mouse clicks either to my application or the other application.

What is an elegant way of doing this?

Example image here. It is a trading application where my application wants to add extra information into the trading application's windows. [URL=http://img104.imageshack.us/my.php?image=windowontop.png][/URL]

Can you be more specific as to what you want to do? There's no elegant way of putting text on another application's window and getting it to stay there, only ugly ways. But you may be able to achieve what you want some other way, depending on your specific situation. — Tim Robinson, May 03 '09 at 08:52

Kevin Montrose · Accepted Answer · 2009-05-04T08:54:01.037

There are no nice ways to do this, but one approach that may work for you is to hook the application in question using SetWindowsHookEx(...) to add a GetMsgProc, which draws your overlay in response to WM_PAINT messages. The basic idea is that you're drawing YOUR graphics right after the application finishes its own drawing.

In your main app:

....
HMODULE hDllInstance = LoadLibrary("myFavoriteDll");
HOOKPROC pOverlayHook = (HOOKPROC)GetProcAddress(hDllInstance, "OverlayHook");
SetWindowsHookEx(WH_GETMESSAGE, pOverlayHook, hDllInstance, threadId);

Off in a DLL somewhere:

LRESULT CALLBACK OverlayHook(int code, WPARAM wParam, LPARAM lParam)
{
  //Try and be the LAST responder to WM_PAINT messages;
  //Of course, if some other application tries this all bets are off
  LRESULT retCode = CallNextHookEx(NULL, code, wParam, lParam);

  //Per GetMsgProc documentation, don't do anything fancy
  if(code < 0) return retCode;

  //Assumes that target application only draws when WM_PAINT message is
  //removed from input queue.
  if(wParam == PM_NOREMOVE) return retCode;

  MSG* message = (MSG*)lParam;

  //Ignore everything that isn't a paint request
  if(message->message != WM_PAINT) return retCode;

  PAINTSTRUCT psPaint;    

  BeginPaint(message->hwnd, &psPaint);
  //Draw your overlay here
  ...
  EndPaint(message->hwnd, &psPaint);

  return retCode;
}

This is all win32 so your C# code will be p/invoke heavy and correspondingly quite ugly. Your DLL must be unmanaged as well (if you intend to inject into a process other than your own), making this an even nastier solution.

This would solve your issue with z-order and clipping issues, as you're rendering into the window itself. However, if the application you're targeting does any drawing outside of the WinProc responding to WM_PAINT things fall apart; this is not an entirely uncommon occurence.

score 2 · Answer 2 · answered Aug 20 '13 at 00:12

2

You might want to draw it on top of directX for games

http://spazzarama.com/2011/03/14/c-screen-capture-and-overlays-for-direct3d-9-10-and-11-using-api-hooks/

answered Aug 20 '13 at 00:12

Barsham

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score 1 · Answer 3 · edited May 23 '17 at 11:53

1

There are problems with z order, clipping, and directing mouse clicks either to my application or the other application.

These are all tasks that the window manager was designed to deal with. You should create a layered window on top of the apps' windows.

See also: Prevent repainting of window in C++

edited May 23 '17 at 11:53

Community

1
1

answered Nov 30 '10 at 12:21

tenfour

36,141
15
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How to draw graphics/text on top of another application

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