Re: cairo & pixmap

[Philip Withnall <philip tecnocode co uk>]

On Sat, 2007-05-19 at 14:12 +0200, control H wrote:
> > The signal handler for the expose event is passed some parameters
> > specifying which part of the screen has become invalidated. If you use
> > these in a Cairo drawing mask, then redraw your canvas, it should be
> > quite fast, as Cairo will ignore all operations to areas outside the
> > mask.
>
> But this means -if I understand correctly- that I still have to redraw
> "from scratch", be it not the complete drawing area but only the
> invalidated part. Therefore, it will still be slower than in my old
> "GDK based" situation, especially when the to be drawn picture becomes
> more complex (which in my situation is the case).

That's how I've done it in programs I've written, but I'm far from an
expert on the subject. There may well be a way to double-buffer the
canvas, and just blit the exposed area from the buffer.

> Do you/does anybody know what the technical reason is why cairo
> contexts fail outside the expose signal? I'm just curious.

I'm not sure what you mean here, sorry.