On 18-3-2013 3:04, Richard wrote:
> ...... What I am
> having trouble with is gradients. I have tried the simple example file in the
> documentation which produces repeating bands of color. However I would like to
> be able to choose two colors to evenly transition between. For example, this
> code:
>
> #include "colors.inc"
>   camera {
>         location <0,4,6 >
>         look_at  <0,0,0 >
> }
> light_source { <2, 4, 3> color White}
>   sphere {
>      <0,0,0>, 2
>      pigment {
>        gradient z       //this is the PATTERN_TYPE
>        color_map {
>          [-4  color Red]
>   [4  color Yellow]
>        }
>        translate -1
>      }
>    }
>
> I thought this should have created a smooth transition from Red to Yellow on the
> entire sphere oriented about the z axis but it has not. Instead it produces
> alternating color bands from yellow to red. Additionally, I tested a gradient in
> the above molecule example but when povray traced the code the section with the
> gradient was no longer transmitting colors through it. So, the two problem I
> need help with are creating a gradient with a smooth transition and making that
> gradient transparent to the molecule underneath it. THANKS!
>
>
To answer the two question, a colour_map goes from 0.0 to 1.0. To adapt 
it to the sphere radius in your example, you have to scale and translate 
it accordingly. I used a gradient x to better show the result. Adding 
the parameter transmit to the color makes it transparant:

  sphere {
     <0,0,0>, 2
     pigment {
       gradient x       //this is the PATTERN_TYPE
       color_map {
         [0  color Red transmit 0.5]
         [1  color Yellow transmit 0.5]
       }
       scale 4
       translate 2*x
     }
   }


Thomas

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