[Synfig-devl] [ synfig-Bugs-1827966 ] Angles are recalculated to 360 mod

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Bugs item #1827966, was opened at 2007-11-07 15:33
Message generated for change (Settings changed) made by genete
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Category: Usability
Group: SVN version
>Status: Closed
>Resolution: Works For Me
Priority: 5
Private: No
Submitted By: Genete (genete)
Assigned to: Nobody/Anonymous (nobody)
Summary: Angles are recalculated to 360 mod 

Initial Comment:
Using svn 1114

Angles that are rounded to 360 module when creating the waypoints.

For example if you set the following values in animation mode to an angle parameter:

frame :: value

0f :: 0.0 DEG
5s :: 1799 DEG

then you get:

0f :: 0.0 DEG
4s23f :: -0.99 DEG
5s :: 1799 DEG (this is -1.00 DEG when rounded to 360 DEG)


You get an smooth angle but a break in the graph.
Also you don't get the number of turns you wanted to achieve when inserted a high angle value. 1799 DEG is almost 5 turns.




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Comment By: Konstantin Dmitriev (zelgadis_ksee)
Date: 2008-04-10 21:56

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> So pick up a
> tangent duck at 30 degrees, turn it through exactly 360 degrees and drop
it
> where you picked it up from and its new angle should be 390 degrees, not
30
> as it currently is.
That behaviour will be appropriate IMHO.


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Comment By: dooglus (dooglus)
Date: 2007-11-08 15:02

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> 3s :: 100 DEG
> 6s :: -100 DEG
> you obtain 100, 110, 120, ... 220, 230, 240, 250, -100.

this is because the shortest way from 100 to -100 is by going through 200. 
Going the other way (100,0,-100) is a turn of 200 degrees, but going this
way (100, 200, 260) is only 160 degrees.  I think that's the way it's
working - taking the shortest route, and treating all x+y*360 angles as x+0
for all y.

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Comment By: dooglus (dooglus)
Date: 2007-11-08 14:59

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After further discussion, it looks like a good solution would be to store
angles as numbers just like reals, without wrapping mod 360.  When
manipulating a tangent using its duck, for instance, the duck should keep a
track of how many rotations the tangent has gone through.  So pick up a
tangent duck at 30 degrees, turn it through exactly 360 degrees and drop it
where you picked it up from and its new angle should be 390 degrees, not 30
as it currently is.

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Comment By: Genete (genete)
Date: 2007-11-07 15:43

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This cause also that you obtain strange movements when inserting values
that are +/- value:

frame :: value

0f :: 0 DEG
3s :: 100 DEG
6s :: -100 DEG

you obtain 

0f :: 0 DEG
3s :: 100 DEG
5s23f :: 257.74 DEG (what is near to 360 DEG - 100 DEG = 260 DEG)
6s :: -100 DEG

So when you expect that the angle do 0, 10, 20, ... 90, 100, 90, 80, ...
10, 0, -10, ... -80, -90, -100
you obtain 0, 10, 20, ... 90, 100, 110, 120, ... 220, 230, 240, 250, -100.


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