Re: [RFC] Gradient fill options

[Pierre <pie...@gm...>]

On 2/2/07, Ethan Merritt <merritt@u.washington.edu> wrote:
> On Friday 02 February 2007 12:38, Hans-Bernhard Br=F6ker wrote:
> > Ethan Merritt wrote:
> > >    gdImageShadedTriangle(gdImagePtr image, gdPoint *vertex, int *colo=
r);
> >
> > > That is, a filled triangle with interpolation of three separate color=
s
> > > specified for the three vertices.
> >
> > Interpolation is quite a tricky business in color space, because there'=
s
> > no clear-cut idea what the curve to draw between two given points in
> > colour space should be.  To properly specify an interpolation mechanism=
,
> > one needs to specify at least the coordinate system in which the
> > interpolated surface in color-space is supposed to be flat.
>
> That is an interesting point.
>
> I noted out in my feature request for libgd that it was unclear what
> sort of interpolation could be done with an indexed colormap. The usual
> shading interpolation routines assume either RGB or CMY colorspace.
> But I think you've answered that question.  The gnuplot PM3D grey
> scale palette routines define a single scale within which interpolation
> of the index value does make sense.  The question then becomes, is
> this linear ordering of index values maintained internally in libgd?
>
> We define colors 1->N sequentially using
>      for(i=3D0;i<N;i++) png_smooth_color[i] =3D gdImageColorAllocate(...)
> Does this yield N successive color indices in libgd? I don't know.

It does.

> We should have plenty of time for testing, discussion, and
> feedback. Gnuplot is headed for an imminent 4.2 release;
> libgd for an imminant 2.0.34 release.  Any work on coordinating
> treatment of gradient-fill can proceed at leisure with an eye
> to much more distant major release targets (4.4/5.0 and 2.1).

I added a sample code in your report. It is a first shot but seems to work =
well.

--Pierre