Some more comments:

On Wed, Dec 05, 2012 at 05:26:56PM +0000, Micael wrote:
> I have made an attempt at optimizing the algorithm as well as the
> performance with big radius dabs.

I have re-run the benchmark, it's good now for big dabs. I haven't
benchmarked small dabs (I think there are some charcoal brushes that make
really a lot of them, if you want to check).

> The overall quality of the antialiasing effect should be better too due a
> previous mistake I had made which is now corrected.  I can't think of a
> way to get rid of the division though.  I believe it's not that much of a
> problem though, since we're only going this way for small radius dabs.

Yes I agree. Another thing: it may be worth double-checking that you never
divide by zero, or something close to it.  If I understood your code right,
this was only a possible problem with very large dabs, so I think it's fine.

> I don't know how to run the benchmark to see the results myself. I have
> tried to "python test_performance.py" but every "print" statement generated
> an error, and after fixing that it complained about the gtk imports.

Sounds like you have run python3 instead of python2. You also need
matplotlib installed (for python2 obviously).

> I wasn't able to spot the step at the threshold value of radius=3.0 with
> both the mouse and a wacom intuos 3. I tested with different brushes, 

I have also tested, and even tried to craft a brush that triggers such a
problem, but I haven't found a way to trigger a glitch, neither.

I didn't really understand the final delta calculations in your code, but
the calculations above look correct to me.  Overall I think the behaviour is
good (with drawbacks mentioned in my other mail), certainly better than the
gappy lines.

-- 
Martin Renold

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