Click and drag in the red box below.
The red box is updated using simple C++ in the
blackdot.cpp file. See the
BD_GenBlackDot function for the code that generates the red bitmap with the black dot. This function
is called from javascript by
this support code, which is called from
this simple javascript code. After generating the updated bitmap, the BD_GenBlackDot C++ function
"returns" the bitmap to the javascript code by calling bd_show_bitmap
here.
That C++ function call results in
this javascript code being called, which calls back the "listener" that was previous registered. That listener is
registered here, giving it the code that actually updates the DOM itself.