Re: [Update REQ 6003]: dithering

[Dellara at washington.engr.ukans.edu]

daemon at geom.umn.edu wrote:
> 
> From: Stuart Levy <slevy>
> Date: Mon, 7 Oct 1996 16:05:15 -0500
> Message-Id: <199610072105.QAA16520 at morse.geom.umn.edu>
> To: software
> Subject: Re: [REQ 6003]: dithering
> 
> > We are trying to use Geomview with our finite element package.
> > A common use will be to shade inside the elements in order to
> > represent the varying quantities. Now I have a question :
> >
> > Is it possible to creat a color map which goes from 0 to 1, such that
> >
> >  at 0.0,   R=0, G=0, B=1  --> Blue
> >  at 0.25   R=0, G=1, B=1  --> Light Blue
> >  at 0.5    R=0, G=1, B=0  --> Green
> >  at 0.75   R=1, G=1, B=0  --> Yellow
> >  at 1.0    R=1, G=0, B=0  --> Red
> 
> Yes, I think so.  You can't easily have geomview apply this color map
> itself, but if you can customize the conversion from your package's data
> into geomview format, you can do this.
> 
> In the description of, say, OFF format (see "man 5 oogl"), note that you
> can specify a four-component (R G B A) color for each vertex,
> using a "COFF" object, as in
> 
> COFF
> 4 4 0           # 4 vertices, 4 faces
> 
> 0 0 0   1 .5 0 1 # vertex at (0,0,0) colored orange
> 1 0 0   0 1 1 1  # vertex at (1,0,0) light blue
> 0 1 0   0 0 1 1  # vertex at (0,1,0) blue
> 0 0 1   .5 1 .5 1 # vertex at (0,0,1) light green
> 
> 3  0 1 2
> 3  2 1 3
> 3  1 0 3
> 3  0 2 3
> 
> Try loading this file into geomview and selecting smooth shading.
> 


Hi:
Your solution is fine if I know where the cutoff points are in my model so that I can specify colors at the vertices properly.
I was looking at your latest release and I see that you have a COLORMAP. Is there any way that I can use such a map on a 
quadrilateral?? 
The colormap which I want, for the following object
COFF
4 1 0
0 0 0     0 0 1   1  # blue
1 0 0     1 0 0   1  # red
1 1 0     1 0 0   1  # red
0 1 0     0 0 1   1  # blue
4 0 1 2 3

will have the following colors at each quarter point
 
blue  -  light blue - green - yellow - Red
0              0.25            0.5           0.75      1.0


how can I define such a map????

     thanks.