GetPixel function returns CLR_INVALID

[smoothie1248]

Hi,
I am trying to use GDI GetPixel function. I first get the DC using
hdc = GetDC(hWnd);
then call GetPixel(hdc,x,y); function. However GetPixel returns -1 which obviously shows that GetPixel cannot read from the dc. I found that I should use GetDeviceCaps to check whether the dc is capable of giving this information. What if it is not? how can I read the RGB values of a position in the window?

Thank you.

 

[obislavu]

Use GetLastError() to get more info when returns CLR_INVALID.
Maybe is enough to retrive RGB using CDC::GetTextColor() , CDC::GetBkColor() and after that CDC::GetNearestColor().
-obislavu-

 

[Cagliostro]

I believe you should ckeck if that pisel is inside the client area of window. Use first GetClientRect. After that check if the point (x, y) is inside of that rect.

Ion Filipski