Q:

Qt drawing icons using color and alpha-map

I would like to draw icons (only one color) in different colors. To do so, I would like to import a single alpha-texture and then combine this with a given color in the application. 
The result should be, that nothing is drawn on to the background, when the alpha-map has an opacity of 0 and the used color should be drawn, when the opacity is 1.
One soulution should be hidden somewhere in QPainter, since you can manually set the Composition-Mode (QPainter::setCompositionMode). But I don't get it to work like I want.
Does somebody have an idea? 
Thanks in advance. 
EDIT: Here is a little graphic explaining what I would like to do. I want to use a Alpha-Map like shown in the graphic and then use a color layer to create my icon. Important is, that the background stays transparent.

A:

You can do thos using QPainter like this:
QColor color;
// set color value

// load gray-scale image (an alpha map)
QPixmap pixmap = QPixmap(":/images/earth.png");

// initialize painter to draw on a pixmap and set composition mode
QPainter painter(&pixmap);
painter.setCompositionMode(QPainter::CompositionMode_SourceIn);

painter.setBrush(color);
painter.setPen(color);

painter.drawRect(pixmap.rect());

// Here is our new colored icon!
QIcon icon = QIcon(pixmap);

Here is gray-scale image and two colored icons which i get using the code above (QPixmap.save() method):
icons

