[cairo] Pattern questions
britten at caris.com
Thu Sep 3 12:40:45 PDT 2009
Chris Wilson wrote:
> For quick questions like these you may find it easier to use IRC, #cairo
> on irc.freenode.net. We lose the advantage of archiving the question and
> answers, but, on the other hand, we may be able to help you better over
I agree. Unfortunately, it's blocked here at work ... :(
I sometimes jump on at home, but I usually don't have my work then :P
>> My goal:
>> - Make a pattern (stencil), and use it to draw multiple times at
>> multiple user positions on my output surface. The result should
>> work for any surface type (But primarily Image and PDF).
>> My concerns:
>> - Correctness (and performance)
>> - Positioning
> Using a sprite or a stencil will be much faster than redrawing a complex
> geometry each time, especially if it involves many layers and expensive
[ snip ]
Yep, I agree on all points. That's why I've been trying to get this
to work, rather than simply re-rendering the sprite at each position...
>> - Is cairo_paint() the correct (and efficient) way to draw each
>> pattern? I had initially been trying to use move_to()/stroke()
>> but obviously that didn't work.
> Yes cairo_paint() is the correct (and efficient) method of applying one
> surface to another.
Ok, good to hear!
>> - I seem to recall discussions about embedding+reusing patterns
>> in some output surfaces (PDF?), and wasn't sure if using paint()
>> would result in that being done (Assuming it actually is done).
> Yes, but pattern reuse is only available in the 1.10 release (you can
> test it in the 1.9.2 snapshot). Snapshotting of patterns is not limited
> to paint, but applies to any use of the pattern.
Fair enough. As long as my code will benefit from the improvements
when they become available, without a rewrite, I'm happy!
>> - Can someone describe (or point me to) some info about positioning
>> the patterns? Especially about where their initial position is.
> This is perhaps the most fundamental part of Cairo's design, everything
> (apart from pens, grr!) is set at the time of setting onto the context.
> In other words, the pattern matrix is set from the current
> transformation matrix at the time of the cairo_set_source() call. All
> subsequent transformations will not alter the position of the source in
> device space. To do that, you will need to either manipulate the pattern
> matrix yourself or reset the source.
Ok, I think I get it. Here's what I ended up with (in my sample app),
to draw my sprites at each of the specific user positions:
int userPosX = 105;
int userPosY = 105;
-(userPosX - userOriginX),
-(userPosY - userOriginY));
and it seems to work. (Critique away...)
[ Even better - I think I've got my 'real' code working! :) ]
> Hope this helps, and you continue to have fun with Cairo!
Immensely! Many thanks!
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