Re: [Gimp-user] Path Tool Problems (fwd)

[Simon Budig <simon budig de>]

Oops, sorry - forgot to have the list in cc as well.

----- Forwarded message from Simon Budig <simon budig de> -----

Subject: Re: [Gimp-user] Path Tool Problems
Date: Fri, 4 Oct 2013 19:38:07 +0200
From: Simon Budig <simon budig de>
To: Akovia <akovia1 eml cc>

Akovia (akovia1 eml cc) wrote:
> If I hover my mouse above a certain segments holding Control, some segments
> will allow to add a node, while other segments won't. This also effects
> deleting line segments.

Weird.

> Now that I think about it I have the last instance on video from a tutorial
> I made. It's kinda perfect since I have it showing my key-presses as well. 
> https://dl.dropboxusercontent.com/u/93550827/Gimp%20Tutorial%20Series/he-is-my-master_full.mkv
> 6:35 to around 8:30 is the problem. I also realized that this also was a
> copied and pasted path.

Really weird. I cannot reproduce this here though. *shrug*

Where did you copy/paste the path from? Inkscape?

> > > 3. Path strokes.
> > >
> > > Quite often on big complicated paths  that I try to stroke, there will
> > > be a few sharp angles that won't protrude out to a point and will just
> > > look like it was cut off.
> >
> > Do you stroke with a tool? Or by "stroke line"? with which options? For
> > the Mitre-Join the Mitre-Limit determines the amount of "allowed
> > protrusion".
> >
> > Can you provide screenshots of the problematic results?
>
> Stroke line mostly unless I'm after some sort of effect. Playing with the
> mitre setting does have some effect on the problem. Maybe I just can't get
> the expected results I want in having an even stroke all the way around.
> Have a look at this and maybe you can explain if there is another way. For
> now I have just been patching some paths together to get what I need..
> https://dl.dropboxusercontent.com/u/93550827/temp/path-stroke_mitre.mkv

Ok, I think what you're seeing there is expected behaviour. The problem
is, that when you move two tangents closely together (i.e. you have a very
sharp corner) the end point of the stroke moves towards infinity, i.e.
you need to cap this at some point. The parameter controlling this is
the mitre limit. We use cairo for rendering and the behaviour is
described as follows in the cairo documentation:

    If the current line join style is set to CAIRO_LINE_JOIN_MITER (see
    cairo_set_line_join()), the miter limit is used to determine whether
    the lines should be joined with a bevel instead of a miter. Cairo
    divides the length of the miter by the line width. If the result is
    greater than the miter limit, the style is converted to a bevel.

    [...]

    The default miter limit value is 10.0, which will convert joins with
    interior angles less than 11 degrees to bevels instead of miters.
    For reference, a miter limit of 2.0 makes the miter cutoff at 60
    degrees, and a miter limit of 1.414 makes the cutoff at 90 degrees.

    A miter limit for a desired angle can be computed as: miter limit =
    1/sin(angle/2)

There is no way to completely disable the miter limit, but maybe the
range of the limit in the UI is not sufficient.

I hope this helps,
        Simon

-- 
              simon budig de              http://simon.budig.de/

----- End forwarded message -----

-- 
              simon budig de              http://simon.budig.de/