Question

Is there any way to let user pick color from screen ? Like the one in GIMP or gcolor2 , you click on anywhere on the screen , and it will tell you the color under mouse.

P.S: QColorDialog doesn’t have the “pick” function

Answer 1

You can grab a one-pixel portion of the entire screen and convert it into a QPixmap:

// crop screen in a pixmap containing only one pixel
QPixmap pixmap = QPixmap::grabWindow(QApplication::desktop()->winId(), mouse_pos_x, mouse_pos_y, 1, 1);
// convert pixmap to QImage so we can access pixel data crossplatform
QImage img = pixmap.toImage(); 
// image has only one pixel at coords (0,0), get its color
QColor col = QColor(img.pixel(0,0)); 

Then it’s easy to extract the color. See function documentation here.