# [cairo] clarification on some misc pattern documents?

Uli Schlachter psychon at znc.in
Sun May 11 12:08:11 PDT 2014

```Hi,

On 11.05.2014 07:07, jimmy frasche wrote:
> - cairo_pattern_get_color_stop_rgba:
>
> "Gets the color and offset information at the given index for a
> gradient pattern. Values of index are 0 to 1 less than the number
> returned by cairo_pattern_get_color_stop_count()."
>
> Is this just saying that the colors stops range from 0 to n-1 where n
> is the result of cairo_pattenr_get_color_stop_count?

yes

> - cairo_pattern_create_mesh
>
> After the Gouraud-shaded triangle example, when talking about
> overlapping patches, the docs begin talking about u and v coordinates
> without defining them.
>
> Skimming the referenced ISO spec for PDFs it appears they refer to the
> axes of the square being deformed, but I wanted to make sure. If so
> perhaps that could be made clearer.

I looked for the word "overlap". Do you mean the following text?

* When two patches overlap, the last one that has been added is drawn
* over the first one.
*
* When a patch folds over itself, points are sorted depending on
* their parameter coordinates inside the patch. The v coordinate
* ranges from 0 to 1 when moving from side 3 to side 1; the u
* coordinate ranges from 0 to 1 when going from side 0 to side
* 2. Points with higher v coordinate hide points with lower v
* coordinate. When two points have the same v coordinate, the one
* with higher u coordinate is above. This means that points nearer to
* side 1 are above points nearer to side 3; when this is not
* sufficient to decide which point is above (for example when both
* points belong to side 1 or side 3) points nearer to side 2 are
* above points nearer to side 0.

I think this tries to define the coordinates when it talks to "range from 0 to 1
when moving from side 3 to side 1".

I feel like I do understand this description. However, feel free to submit
enhancements which you think are necessary.

Cheers,
Uli
--
"Why make things difficult, when it is possible to make them cryptic
and totally illogical, with just a little bit more effort?" -- A. P. J.
```

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