# [cairo] New user question. How do I fill inside of a curve?

Jody Winston josephwinston at mac.com
Thu Jan 3 12:11:45 PST 2008

```Thanks for the tip.  The real issue was how I was drawing the curve.  I
was using move_to, line_to in succession rather than move_to, line_to,
line_to, etc.

Bill Spitzak wrote:
> Add this to your path to make a closed shape (minx and maxx are the
> x coordinate of the first and last points):
>
>     lineto(maxx, 0);
>     lineto(minx, 0);
>     closepath
>
> If you fill this shape it will fill the areas you want, but all with
> the same color.
>
> So you then must draw it twice with two different clip rectangles, one
> with the bottom edge at y=0 and the other with it's top edge at y=0.
>
> Alternatively it may be possible to set the source to an image or
> gradient to put the correct color in with one fill.
>
> Jody Winston wrote:
>> First of all, thanks for the help with my first attempt at Cairo.  I
>> also am apologizing for munging the email headers by hand but I do
>> not have the original email chain with me.
>>
>> I think that I did everything you suggested and have attached a
>> standalone example with your changes, but I still am having problems.
>>
>> What I am attempting to do is color the area of a curve that either
>> is above or below the line y = 0 as quickly as possible since I have
>> a large number of these curves to process.
>>
>> The problem might be best expressed by looking at a contrived
>> example. Given a curve defined by [(-100, -100), (100, 100), (200,
>> -200), (300, 300)].  I need to color the triangles [(0, 0), (100,
>> 100), (400/3, 0)] and [(240, 0), (300, 300), (300, 0)] with one color
>> since they are the areas of the curve that are between y = 0 and the
>> curve itself. Likewise, I need to color the triangles [(-100, -100),
>> (-100, 0), (0, 0, 0)] and [(400/3, 0), (240, 0), (200, -200)] since
>> they are between the curve and the line y = 0.

```

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