Re: [Lib2geom-devel] Mandatory path stitching

[Johan E. <jbc...@sw...>]

That sounds even better, actually.

Good stuff,
   Johan


On 29-3-2015 20:43, Krzysztof Kosiński wrote:
> How about flipping the default, i.e. normally exceptions are raised
> just before stitching would occur, but you can disable them?
>
> This is similar to the previous behaviour, but would raise errors in
> sloppy code at the point where invalid values are inserted into the
> path, not when someone later tries to use the broken path.
>
> Regards, Krzysztof
>
> 2015-03-29 12:38 GMT+02:00 Johan Engelen <jbc...@sw...>:
>> Stitching, i.e. adding segments, is not a good solution to floating point
>> rounding problems. IIRC, most of 2geom explicitly sets end-points to the
>> same value, solving rounding problems. You have to push 2geom pretty hard to
>> have it generate non-continuous paths. When adding little segments to paths
>> that generate discontinuities for some operations, I think the problem only
>> escalates.
>> (Side point: from what I remember, many of the non-continuity exceptions
>> arise because of user code pushing NaN points to the path. That's not going
>> be solved by stitching.)
>>
>> In any case, I am simply giving my input having used 2geom a lot in
>> Inkscape, but I don't expect to be writing code with/for it in the near
>> future.
>> I don't see why stitching should be implied default behavior. Stitching is
>> useful, but isn't it really just a hack? My course of action would be to
>> remove the default Stitching value for all functions that take a Stitching
>> argument.
>>
>> - Johan
>>
>>
>>
>> On 29-3-2015 0:25, Nathan Hurst wrote:
>>> It's not sloppy code, it's inescapable floating point rounding.
>>>
>>> njh
>>>
>>> On Sat, Mar 28, 2015 at 10:29:07PM +0100, Johan Engelen wrote:
>>>> I understood what you wrote.
>>>> I argued that the default of allowing sloppy code is probably not a good
>>>> default.
>>>>
>>>> - Johan
>>>>
>>>>
>>>> On 28-3-2015 17:24, Krzysztof Kosiński wrote:
>>>>> A non-contiguous path is practically always an error, so it makes
>>>>> sense to either prevent it or report it as early as possible. Now the
>>>>> default behavior is to add those extra segments, which allows sloppily
>>>>> written code to function as expected, but you can call
>>>>> setStitchExceptions() to enable the throwing of exceptions whenever a
>>>>> stitch segment would be appended.
>>>>>
>>>>> Regards, Krzysztof
>>>>>
>>>>> 2015-03-28 13:09 GMT+01:00 Johan Engelen <jbc...@sw...>:
>>>>>> On 27-3-2015 20:48, Krzysztof Kosiński wrote:
>>>>>>> Every method that modifies a Path has an optional argument called
>>>>>>> "stitching" that determines whether additional segments are added to
>>>>>>> make the path continuous. By default, stitching is not used. If there
>>>>>>> are any discontinuities, calling some of Path will cause an exception
>>>>>>> to be thrown, which in most cases means a crash.
>>>>>>>
>>>>>>> I want to make stitching mandatory. Since in some cases you want to be
>>>>>>> sure that no stitching happens in your code, there will be an extra
>>>>>>> boolean member variable. When set to true, it will throw an exception
>>>>>>> whenever you try to insert a discontinuity into the path.
>>>>>>>
>>>>>>> Is everyone OK with this idea?
>>>>>> I am not so sure about this.
>>>>>> It may not be very helpful if 2geom automatically fixes "user errors",
>>>>>> leading to unexpected results. If you change the default behavior (from
>>>>>> not stitching to stitching), user code will suddenly behave different
>>>>>> perhaps without the user knowing (e.g. no compiler error).
>>>>>> How about making the _choice_ for stitching behavior mandatory?
>>>>>>
>>>>>> -Johan
>>>>>>
>>>>>>
>>>>>>
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