Implementing SVG attribute "stroke-miterlimit" ( tdf#48066)

[Armin Le Grand]

Hi Regina,

yes, the MiterLimits are different in different systems, but all are 
somehow specified using the angle between the two vectors involved. I 
remember to have seen some definitions, most using the same and 15 as 
default value. The ways to be compatible with MS are:
- find a definition somewhere, mqaybe in forums or newsgroups (I have 
none, sorry)
- reverse engineer by trying out. Probability is high that there is a 
(linear?) relationship between the values, so it might be a simple scaling
HTH!

Regards,
Armin

Am 07.04.2016 um 14:35 schrieb Regina Henschel:
> Hi all,
>
> I have made some progress. But a new problem comes up.
>
> I have changed WinSalGraphicsImpl::drawPolyLine [3] so that it gets an 
> additional parameter fMiterMinimumAngle (same meaning as in 
> createAreaGeometryForJoin) and uses it for gdi+. The rendering in 
> edit-mode in Draw and Impress is correct then with gdi+ on Windows. 
> Even Text in SVG works out of the box. [BTW: The current rendering 
> using gdi+ is wrong, see my report bug#99102.]
>
> The behavior of gdi+ is described in [1]. To get the same kind of 
> behavior as in LO, when the miter limit is exceeded, the LineJoin type 
> 'LineJoinMiterClipped' has to be used.
>
> Being only in LibreOffice and SVG, that would be no problem. But MS 
> seems to use different defaults. The rendering in PowerPoint looks 
> like gdi+ type 'LineJoinMiter'. The specification for 'lim' in 
> ECMA-376, Part 1, chapter 20.1.8.43, has no details, and I have not 
> found details otherwhere.
>
> This gdi+ type 'LineJoinMiter' kind of clipping (see the image in the 
> article [1]) will be used in SVG 2 [2] too under the identifier 
> 'miter-clip'.
>
> So my question: Ignore interoperability with MS? If not, how to solve it?
>
> Kind regards
> Regina
>
> [1] 
> https://msdn.microsoft.com/en-us/library/windows/desktop/ms534148%28v=vs.85%29.aspx
>
> [2] https://www.w3.org/TR/svg-strokes/#StrokeShape
>
> [3]
> diff --git a/vcl/win/gdi/gdiimpl.cxx b/vcl/win/gdi/gdiimpl.cxx
> index 7febbe8..36ecb31 100644
> --- a/vcl/win/gdi/gdiimpl.cxx
> +++ b/vcl/win/gdi/gdiimpl.cxx
> @@ -2031,7 +2031,8 @@ bool WinSalGraphicsImpl::drawPolyLine(
>      double fTransparency,
>      const basegfx::B2DVector& rLineWidths,
>      basegfx::B2DLineJoin eLineJoin,
> -    css::drawing::LineCap eLineCap)
> +    css::drawing::LineCap eLineCap,
> +    double fMiterMinimumAngle)
>  {
>      const sal_uInt32 nCount(rPolygon.count());
>
> @@ -2064,9 +2065,9 @@ bool WinSalGraphicsImpl::drawPolyLine(
>              }
>              case basegfx::B2DLineJoin::Miter :
>              {
> -                const Gdiplus::REAL aMiterLimit(15.0);
> +                const Gdiplus::REAL 
> aMiterLimit(1/sin(fMiterMinimumAngle/2.0));
> Gdiplus::DllExports::GdipSetPenMiterLimit(pTestPen, aMiterLimit);
> -                Gdiplus::DllExports::GdipSetPenLineJoin(pTestPen, 
> Gdiplus::LineJoinMiter);
> +                Gdiplus::DllExports::GdipSetPenLineJoin(pTestPen, 
> Gdiplus::LineJoinMiterClipped);
>                  break;
>              }
>              case basegfx::B2DLineJoin::Round :
>
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