Re: Cairo context creation problem

"Jianshi Huang" <[email protected]> writes:

> The code I used below is a little bit different to the testcairo
> examples. In testcairo, cairo context is created within the callback
> of expose-event, while in  my code, I want to initialize the context
> and set it to a global variable, so that I don't need to pass it
> around.

You could just as well use the with-cairo-context macro to bind a fresh
context to special variable when you need to do some rendering. This
will ensure that the context is valid every time you use it. On the down
side, you'll have to initialize it with the correct attributes on every
expose event (or user invocation in an interactive system), but the
overhead in doing so would be very small.

> But running the program, there were errors told me that The slot
> GTK:WINDOW is unbound in the drawing-area object.
> 
> After an hour of debugging, I finally found that if I place
> gdk:cairo-create after gtk:widget-show-all, then it works.
> 
> So I'm wondering if it's caused by the initialization sequences in clg.

Yes, this has to do with the internal workings of Gtk+ it self.
 
> And do you have any suggestions for using cairo efficiently in clg
> (like being a graphics editor within a scrolled-window)

I am not sure what exactly you mean by using cairo efficiently. A
general advice if rendering speed is of concern, is to do as much
polygon simplification and clipping as possible in Lisp. This tends to
give some speedup, as Cairo is not as fast as it probably could be. This
is at least my experience and may change in the future as more
optimization is done in Cairo.

-- 
Espen

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