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From Armin Le Grand <Armin.Le.Gr...@me.com>
Subject Re: Arrow heads with hole
Date Tue, 03 Dec 2013 17:05:23 GMT
     Hi Regina,

On 02.12.2013 23:45, Regina Henschel wrote:
> Hi Andrea,
>
> Andrea Pescetti schrieb:
>> On 26/11/2013 Regina Henschel wrote:
>>> I have expanded the standard.soe with some arrow heads with hole. The
>>> file is attached to 
>>> https://issues.apache.org/ooo/show_bug.cgi?id=123758.
>>> If you like them, we can consider to use this palette as default.
>>
>> I added a screenshot to the issue for clearer comparison. The new styles
>> are nice and it would be good to have them in 4.1.
>>
>> In some cases, in the preview, I see the main line of the arrow going
>> (seemingly) too far within the arrow head, see
>> http://imagebin.org/280257 for an example. Is this wanted?
>
> No, that is not wanted. I will explain the problem in more detail:

First: nice arrowheads! I am currently on something else, but I have 
already a grep on the task which you wrote.

Background:
- The arrows traditionally only used polygons (topologically: no 
poly-polygons which allows holes). This is alrteady changed and implemented.
- The arrow heads and line overlapping traditionally use a 0.0 or 0.8 
factor of overlap, according to 0% or 80% overlap. These values are 
handles relative to the arrow head sizes already, but are treated as a 
boolean (one or the other). In the core these values are prepared to be 
0-100%, freely choosable. In the UI you can switch between 0% and 80% in 
the lines dialog in it's first page (line ends-> 'centered' for right 
and left arrow). Missing is to have a value input instead of that simple 
switch and to get that 0-100% value over the API and to ODF. This is 
where normally Regina knows if this is possible ;-)
Thus: Old. historical limitations, some more way to go to get over 
these. When one day it will be possible to choose that value freely 
(prepared in core and primitives) you will be able to trim these to 
connect to your arrow head as you want it to be.
If there would be a way to do this automatically could also be 
considered; the old overlapping paint was probably only implemented 
since no one wanted to do it better from the beginning (time constrains? 
other?).

Regina, this sounds as if we could use a feature task for his...

>
> If you stop the line at the very place where the arrow head starts, 
> you get a visible gap between the "square 45°" and the line itself for 
> fat lines (and same for circle or any peak shape). Therefore an 
> overlap was introduced. For the filled arrow heads, it does not matter 
> whether the line is drawn a little bit longer.
>
> For the arrow heads with hole you have to find a compromise between 
> showing a gap at the outer part and showing a little bit line in the 
> hole.
>
> Currently the amount by which the line is drawn longer does not depend 
> on the kind of arrow head, but on the length of the arrow head. It is 
> in file polygonprimitive2d.cxx in method 
> PolygonStrokeArrowPrimitive2D::create2DDecomposition around line#547 
> the statement "fStart *= 0.8;"
> In LO I have changed that to "fStartOverlap = getStart().getWidth() / 
> 15.0;", so that it depends on the width of the arrow head, which also 
> determines the 'stroke' width in the non-filled arrow heads. It is a 
> compromise too. (It is not really a 'stroke', but the area between two 
> combined paths.)
>
> We could copy that in AOO. But perhaps someone has a better idea?
>
> Kind regards
> Regina
>
>
>
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