[cairo] Fwd: SVG to EMF quality

[Shixin Zeng]

Forwarding with zipped attachment

Best Regards

Shixin Zeng




---------- Forwarded message ----------
From: Shixin Zeng <zeng.shixin at gmail.com>
Date: Tue, Oct 13, 2009 at 12:30 AM
Subject: Re: [cairo] SVG to EMF quality
To: Adrian Johnson <ajohnson at redneon.com>
Cc: cairo at cairographics.org


Hi, Adrian

Thanks for that patch, but I'm sorry to say that it doesn't seem to
improve anything, at least to my eyes.

I found your emf was deleted, I pulled it a month ago, so I still have
that patch. I'm sorry for responding so late, but it took me quite a
time to compile cairo and librsvg(which turns out to depend on gtk) on
windows.

The output is attached.

axial2.emf is produced this the cairo with your patch, axial.emf is
produced by pristine cairo, and axial.svg is the source.

Best Regards

Shixin Zeng



On Wed, Sep 9, 2009 at 9:07 AM, Adrian Johnson <ajohnson at redneon.com> wrote:
> Shixin Zeng wrote:
>>
>> Hi,
>>
>> I've produced some pictures with matplotlib for my paper, which
>> prefers enhanced MetaFile (EMF). However, current maplotlib doesn't
>> support EMF output, but svg. So I tried to convert svg to emf via
>> cairo, as mentioned in this
>>
>> thread:http://lists.cairographics.org/archives/cairo/2009-January/016215.html
>>
>> But the problem is that the quality of the output emf file is pretty
>> low. Is this caused by my badly programming or the limitation of this
>> method itself? Thanks
>
> After discovering EMFexplorer [1] and examining some different EMF files I
> have found the cause of the low quality EMF output from the win32-printing
> surface.
>
> In GDI all path functions use integer coordinates. For small drawings this
> causes rounding problems. Using EMFexplorer I could see that other
> applications were scaling down the GDI current transformation matrix and
> scaling up path coordinates to increase the precision.
>
> This was something I previously tried with the win32-printing surface
> without success. Using EMFexplorer to check the output I could immediately
> see what the problem is. The win32-print surface is resetting the GDI CTM to
> identity to preventing rounding errors when printing where the GDI units are
> in dpi.
>
> The patch on my emf branch [2] is an initial attempt at fixing this. It
> needs further testing to ensure I have not caused any regressions when
> printing. With this patch it is possible to get good EMF output with the
> following code:
>
> void create_emf (char *filename)
> {
>    HDC dc;
>    HDC ref_dc;
>    XFORM xform;
>    cairo_surface_t *surface;
>    cairo_t *cr;
>
>    ref_dc = GetDC (NULL);
>    dc = CreateEnhMetaFile (ref_dc, filename, NULL, NULL);
>    ReleaseDC (NULL, dc);
>
>    /* Scale the GDI CTM by 1/16. This allows all coordinates to
>     * be scaled up by 16 to increase precision */
>    SetGraphicsMode (dc, GM_ADVANCED);
>    xform.eM11 = 1.0/16;
>    xform.eM12 = 0;
>    xform.eM21 = 0;
>    xform.eM22 = 1.0/16;
>    xform.eDx = 0;
>    xform.eDy = 0;
>    SetWorldTransform (dc, &xform);
>
>    surface = cairo_win32_printing_surface_create (dc);
>    cr = cairo_create (surface);
>
>    /* Undo the scale applied to the GDI CTM */
>    cairo_scale (cr, 16, 16);
>
>    draw (cr);
>    cairo_destroy (cr);
>    cairo_surface_destroy (surface);
>    CloseEnhMetaFile (dc);
> }
>
>
> [1] http://frazmitic.free.fr/emfexplorer/
> [2] http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=emf
>
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