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Getting screen pixel colour (Visual C++)

Posted on 2003-02-28
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Last Modified: 2012-05-04
This is a Visual C++ question.
I was wondering if there is a way to the current pixel colour at the absolute position(x,y). i.e. Colour being displayed anywhere on the screen, not just the current program.
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Question by:The_Flash
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5 Comments
 
LVL 9

Accepted Solution

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Priyesh earned 100 total points
ID: 8046543
CWnd* pWnd = CWnd::GetDesktopWindow() ;
CDC* pDC = pWnd->GetDC() ;

COLORREF clr = pDC->GetPixel(100, 100) ;

pWnd->ReleaseDC(pDC) ;
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LVL 6

Expert Comment

by:PlanetCpp
ID: 8046710
just to show you in non MFC
HWND desktop = GetDesktopWindow();
HDC desktopHdc = GetDC(desktop);
COLORREF color = GetPixel(desktopHdc,1,1);
ReleaseDC(desktop,desktopHdc);

if you need to extract the rgb values then use this way
     int red,green,blue;
     red=green=blue=0;

     COLORREF color = RGB(255,100,50);

     //COLORREF is stored as 0x00bbggrr, so..
     blue = (color/65536) & 255;
     green = (color/256) & 255;
     red = color & 255;

     cout<<"Red = "<<red;
     cout<<"\nGreen = "<<green;
     cout<<"\nBlue = "<<blue<<endl;
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LVL 1

Expert Comment

by:frogger1999
ID: 8046794
That doesn't seem to work for me, but the C way does


<<<<<<<<<<<<THIS WORKS

    HDC dc = GetDC(NULL);
    COLORREF result = GetPixel(dc, 700, 250);
    ReleaseDC(NULL, dc);

<<<<<<<<<<<<<<


in the MFC version I get result as 0xffffffff (CLR_INVALID)

because per the documentation

"The return value is the RGB value of the pixel. If the pixel is outside of the current clipping region, the return value is CLR_INVALID."

however

<<<<<<<<<<<<<<<<<<<<THIS ALSO WORKS

    HDC dc = GetDC(NULL);
    CDC pDC;
    pDC.Attach(dc);
    COLORREF clr = pDC.GetPixel(700, 250);

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

but the c version of

HWND wnd = GetDesktopWindow();
HDC dc = GetDC(wnd)
...

doesn't

so it seems that there is something wrong with getting the desktop window and querying it for a color....

Priyesh:  if you know what is the equivelant in MFC for

GetDC(NULL);


 
0
 

Author Comment

by:The_Flash
ID: 8047072
Privesh, your code didn't seem to work on windows, only the desktop.
I modified it so it grabbed a window from it's position.

// Any point in which the window current occupies
Point * point(220,340);
CWnd * pWnd = WindowFromPoint( point );
CDC * dc = pWnd->GetDC();
COLORREF color = dc->GetPixel(51,173);
pWnd->ReleaseDC(dc);

After a bit of frustration and testing, I found out that if it is a broswer window, which it what I was wanting it to work for, every object on the page is treated as a seperate window.
In the case that I was testing, there were 3 flash movies in the page, and each was treated as a different window.
0
 

Author Comment

by:The_Flash
ID: 8047078
I halved the points as it didn't give me the solution, although it did lead me o it.
0

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