Interdependent adjustments conundrum

["Daniel Haude" <dunno stoptrick com>]

Hello,

For argument's sake, let's consider the following situation: There are  
four GtkAdjustments: A, B, C, D, with corresponding values a, b, c, d,  
each linked to a GtkSpinButton (which probably doesn't matter). The  
following condition is supposed to be always true: d = a + b + c.

I wrote two callbacks: One is called on a "value-changed" signal of either  
A, B, C; it builds the sum d = d = a + b + c and calls  
gtk_adjustment_change_value(D, d). This part, of course, works.

Now to adjustment D: When the user changes D, I want A thru C to assume  
some default distribution with a = d/4, b = d/4, c = d/2. Of course, if I  
plug these values into A thru C, they in turn change their value and send  
the result back to D.

Not only that; all four values are supposed to be integers which  
introduces rounding issues: If the user changes D to 10, the resulting  
values are a = 2, b = 2, c = 5 which results in d = 9. This is the  
behavior I want; however, this in turn emits another "value-changed" on D  
which results in c = 4, d = 8 at which point the signal rigmarole finally  
settles.

The behavior I need is this: If the user changes any one of A thru C, D is  
updated accordingly. If he changes D, A thru C are filled with the default  
split and D is updated to the resulting value without disturbing A thru C  
another time round.

How is this accomplished?

I looked at g_signal_handler_block(); I do have the signal IDs (using some  
ugly external global variables) but I can't figure out what the "instance"  
argument is supposed to mean. But even if I could I wouldn't know how to  
use it because where would I put it? Somehow D must distinguish the  
value-changes of A, B, C that were caused by direct user interaction from  
those that are a result of D issuing changes on A, B, C.

Thanks,
--Daniel