[cairo] Gradient mesh rasterizer

[Bill Spitzak]

Adrian Johnson wrote:
> Andrea Canciani wrote:
>> On Mon, Jul 27, 2009 at 10:31 PM, Andrea Canciani<ranma42 at gmail.com> wrote:
>>> I updated my code to be pixel perfect when painting a square (the file
>>> pattern.c does exactly this: it paints a 768 x 768 square tile and
>>> reports for any incorrect pixel).
>>> I also have this code as a patch against the mesh branch.
> 
> The mesh branch is at:
> 
> http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=mesh
> 
> Currently the image, PDF, and PostScript backends are working. The new 
> API is:
> 
> 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_add_control_point (cairo_pattern_t *pattern,
>   				 double x,
>   				 double y);
> 
> Currently the the cairo_pattern_add_color_stop_rgb[a] functions are used 
> for adding color stops. After each side of a patch is specified, using 
> cairo_pattern_curve_to() or cairo_pattern_line_to(), 
> cairo_pattern_add_color_stop_rgb[a] can be used to add one or more stops 
> along the current side.
> 
> However at present both the gradient rasterizer and the PDF/PS backends 
> only allow color stops on the corners of the patch. Only the first stop 
> specified for each side is used and is assumed to be at offset 0.
> 
> I'm not sure if the API should be changed to allow only color stops on 
> the corners, or if stops should be allowed anywhere on the sides and 
> then subdivide the patch at the stops when rendering or embedding in PS/PDF.

Can the patch have any number of sides or is it required to have 4?