to many invalidate_rect calls freezes window

[buergi <pat_buergi124 gmx de>]

Hello,

I'm developing an application with 2 threads: one worker thread and one
which runs the GTK mainloop. The worker thread uses a sigc signal to
move a cursor step by step over a DrawingArea in the main thread.
The whole thing should simulate a XY plotter with stepper motors, thus
the single step movements are important.

So i defined
	sigc::signal<void,STEP_DIRECTION> step_command;
in the main thread and pass it to the worker thread and call it e.g. in
a loop like
	for (int i=0;i<100;i++)	step_command(STEP_UP);

The new cursor position in the main thread gets set in
	void MainDrawArea::on_signal_step_command(STEP_DIRECTION dir)
The cursor's region on the DrawingArea gets invalidated before and after
the new cursor position gets set:
	Gdk::Rectangle rect(cursor.x-10,cursor.y-10,20,20);
	window->invalidate_rect(rect,false);

The cursor is drawn in the on_expose_event() method.

Everything works that far, but the cursor moves a bit slow.
Seems this communication by sigc signal is not very efficient. I think
i'll use asynchronous GTK's or sigcx's Dispatcher instead of sigc's signals.
(better ideas are welcome, but single step movements are important)


The problem which i have is that although i called invalidate_rect the
cursor gets redrawn only for a few steps and freezes then.
But not only the cursor movement freezes, the whole window doesn't get
redrawn any longer. Moving it out of the screen and back in creates ugly
artifacts. Resizing the window or clicking a button redraws it correctly
as expected.

I could solve the problem by using window->process_update(false); after
the invalidate_rect call which makes the cursor being redrawn as expected.

Perhaps i filled the update area with to many rectangles, i've no idea
why it doesn't work.
Does anyone have an idea how to solve this problem without the
process_update? Or what i'm actually more interested in is the reason
why it doesn't work.


thanks in advance

buergi