[cairo] Mesh gradients

[Andrea Canciani]

Sorry for reopening a very old thread, but I started reworking the
code to merge it
in master, so I think that this might be an appropriate time to
discuss about the
API for mesh patterns.

On Mon, Sep 7, 2009 at 1:06 AM, Behdad Esfahbod <behdad at behdad.org> wrote:
> Hi Adrian,
>
> My main comment is that given the number of new API additions, I'd rather see
> them under a cairo_pattern_mesh_* namespace rather than cairo_pattern_*.

Yes, this looks like a good idea.

> Other than that, not a huge fan of moveto/lineto/curveto, but can live with it.

I'm not very keen on them, but so far they are probably the easiest way that
has been proposed to specify patches.

One problem of the current API is that it should be made clear that the order
used to specify the patch is important (in particular the patch with A,B,C,D as
edges is different, in general, from the patch D,A,B,C).

A different API might make it more obvious, but I'm unable to figure out how
we could do it.

Andrea

>
> Thanks for all the work,
>
> behdad
>
> On 09/06/2009 08:45 AM, Adrian Johnson wrote:
>> I've updated the mesh gradient API on my mesh branch[1] to change the
>> set corner color and set control point API to:
>>
>> void
>> cairo_pattern_set_corner_color_rgb[a] (cairo_pattern_t *pattern,
>>                                      int point_num,
>>                                      double red, double green,
>>                                          double blue);
>> void
>> cairo_pattern_set_control_point (cairo_pattern_t *pattern,
>>                                int point_num,
>>                                double x,
>>                                double y);
>>
>> I found this change to be easier and less confusing to use. The complete
>> API is at the end of this message. The gtk-doc dcoumentation in the code
>> documents the use of this API. The mesh branch also includes some
>> patches from Andrea to fix some bugs.
>>
>> I've updated the cairo backend of poppler to use cairo mesh gradients[2]
>> for PDF Type 4,5,6, and 7 shadings. Some sample renderings of PDF files
>> using this poppler-cairo branch are at:
>>
>> http://people.freedesktop.org/~ajohnson/mesh/
>>
>> monkey.png, rendered from monkey.pdf, is from laidout [3]. The others
>> are from smooth shading samples [4] converted to PDF then rendered with
>> poppler-cairo. Some of these have a few white pixels in them. I have not
>> worked out what is causing that.
>>
>> Any comments on this API and the implementation? Should the mesh
>> gradient rasterizer be moved into pixman?
>>
>>
>> [1] http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=mesh
>>
>> [2] http://cgit.freedesktop.org/~ajohnson/poppler/log/?h=mesh
>>
>> [3] http://www.laidout.org/
>>
>> [4]http://partners.adobe.com/public/developer/en/ps/sdk/sample/smooth.zip
>>
>>
>> Complete Mesh gradient API
>> --------------------------
>>
>> cairo_pattern_t *
>> cairo_pattern_create_mesh (void);
>>
>> void
>> cairo_pattern_begin_patch (cairo_pattern_t *pattern);
>>
>> void
>> cairo_pattern_end_patch (cairo_pattern_t *pattern);
>>
>> void
>> cairo_pattern_curve_to (cairo_pattern_t *pattern,
>>                       double x1,
>>                       double y1,
>>                       double x2,
>>                       double y2,
>>                       double x3,
>>                       double y3);
>>
>> void
>> cairo_pattern_line_to (cairo_pattern_t *pattern,
>>                      double x,
>>                      double y);
>>
>> void
>> cairo_pattern_move_to (cairo_pattern_t *pattern,
>>                      double x,
>>                      double y);
>>
>> void
>> cairo_pattern_set_corner_color_rgb (cairo_pattern_t *pattern,
>>                                   int point_num,
>>                                   double red, double green,
>>                                       double blue);
>>
>> void
>> cairo_pattern_set_corner_color_rgba (cairo_pattern_t *pattern,
>>                                    int point_num,
>>                                    double red, double green,
>>                                        double blue, double alpha);
>>
>> void
>> cairo_pattern_set_control_point (cairo_pattern_t *pattern,
>>                                int point_num,
>>                                double x,
>>                                double y);
>>
>> cairo_status_t
>> cairo_pattern_get_patch_count (cairo_pattern_t *pattern,
>>                              int *count);
>>
>> cairo_path_t *
>> cairo_pattern_get_path (cairo_pattern_t *pattern,
>>                       int patch_num);
>>
>> cairo_status_t
>> cairo_pattern_get_corner_color_rgba (cairo_pattern_t *pattern,
>>                              int patch, int corner,
>>                              double *red, double *green,
>>                              double *blue, double *alpha);
>>
>> cairo_status_t
>> cairo_pattern_get_control_point (cairo_pattern_t *pattern,
>>                                int patch, int point,
>>                                double *x, double *y);
>>
>>
>> _______________________________________________
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>> cairo at cairographics.org
>> http://lists.cairographics.org/mailman/listinfo/cairo
>>
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