When a container receives a call to the draw function, it must send synthetic draw calls to all children that don’t have their own Windows.
This function provides a convenient way of doing this. A container, when it receives a call to its
draw function, calls propagate_draw once for each child,
passing in the cr the container received.
propagate_draw takes care of translating the origin of cr, and deciding whether the draw needs
to be sent to the child. It is a convenient and optimized way of getting the same effect as calling
draw on the child directly.
In most cases, a container can simply either inherit the draw implementation from Container, or do some drawing and then chain to the draw implementation from Container .
| this | |
| child |
a child of this |
| cr |
Cairo context as passed to the container. If you want to use |