get the point colour

When somebody clicks on a window or any place in the client area, how do get the color of the point where the mouse if clicked.


Actually, I want to make a color picker.

Something like this: (i haven't tested it)

PHP Code:

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BUTE Red,Green,Blue;
POINT Mouse;
GetCursorPos(&Mouse);
COLORREF Colors;
Colors = GetPixel(GetWindowDC(ChildWindowFromPoint(WindowFromPoint(Mouse), Mouse)), Mouse.x, Mouse.y);
            
Red = GetRValue(Colors);  //contains red value
Green = GetGValue(Colors);  //contains green value
Blue = GetBValue(Colors); //contains blue value 


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But If I put that in a some event like "WM_MOSEMOVE" then I want to write the value that I get so that I know if that code is working. I have tried to show a messagebox with one the values in but it gives me the following error:

Code:

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error C2664: 'MessageBoxA' : cannot convert parameter 2 from 'unsigned char' to 'const char *'
        Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast

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I used the following code to show a messagebox with the red and blue values in:

Code:

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case WM_MOUSEMOVE:
GetCursorPos(&Mouse);
Colors = GetPixel(GetWindowDC(ChildWindowFromPoint(WindowFromPoint(Mouse), Mouse)), Mouse.x, Mouse.y);
           
        Red = GetRValue(Colors);  //contains red value
        Green = GetGValue(Colors);  //contains green value
        Blue = GetBValue(Colors); //contains blue value
        MessageBox(NULL,Red,"Hi",MB_OK);
                return 0;

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Use the itoa function to use the red var in a messagebox.
Also i think it is not a good idea to pop up a messagebox on the mousemove message.

I am using the messageboxes for just testing so that I know I am getting the right value.


Let me test and if it does not work then I will reply again...

Here is the code that I use. But I always shows me the value "192" for every color(Red, Green, Blue)
Even if I change my windows' color, it stays the same:

Code:

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case WM_LBUTTONDOWN:

Colors = GetPixel(GetWindowDC(ChildWindowFromPoint(WindowFromPoint(Mouse), Mouse)), Mouse.x, Mouse.y);
           
Red = GetRValue(Colors);  //contains red value
Green = GetGValue(Colors);  //contains green value
Blue = GetBValue(Colors); //contains blue value
hdc = GetDC(hwnd);
TextOut(hdc, 30,50,itoa(Red, buffer,10), 3);
TextOut(hdc, 80,50,itoa(Blue, buffer1,10), 3);
TextOut(hdc, 130,50,itoa(Green, buffer2,10), 3);
                ReleaseDC(hwnd, hdc);
return 0;

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I am drawing the text when the left button is clicked. So I also have problem with the PAINT event because whenever I resize my window, it just repaints the whole area and I loose my text.

How can I fix both of these?

If you dont mind it, you can write a tiny ActiveX DLL in VB using its "point" function....... Just pass it the x and y.... and it will return pixel color

That kind of defeats the object of using C++ though ;)

The GetPixel API is a lot faster than the Point function, and is more efficient when using C++.

Even if you did make a VB DLL, you'd have to include the runtime files.