Rendering a gradient with uv_mapping seems to have a bug when
using the gradient pattern: no mapping is done with gradient z ! With
gradient x and gradient y it renders fine. This is the case with the
sphere, lathe and box objects.
Rendering a bicubic_patch with uv_mapping has a problem with all
gradients. With gradient x the gradient goes in the z-direction. With
gradient y it goes in the x-direction and with gradient z no mapping is
done.

Rendering the scene below will show the problem. The top row shows
gradient x, gradient y and gradient z with the 'classic' gradient.
The bottom row shows the same gradients with uv_mapping.

//************** Scene with uv_mapping bug ? *************
// Change Obj_Switch for different objects
#declare Obj_Switch = 0; //0 =Sphere;  1= Lathe;  2= Bicubic_patch

#declare C_Map =
        color_map {
                [ 0.0 color rgb < 1.0, 1.0, 1.0 > ]
                [ 0.3 color rgb < 1.0, 1.0, 1.0 > ]
                [ 0.3 color rgb < 1.0, 0.0, 0.0 > ]
                [ 0.6 color rgb < 1.0, 0.0, 0.0 > ]
                [ 0.6 color rgb < 0.211505, 0.530358, 0.728481 > ]
                [ 1.0 color rgb < 0.211505, 0.530358, 0.728481 > ]
        }

#if (Obj_Switch = 0)
        #declare Object = sphere  { < 0.0, 0.0, 0.0 >, 0.5 }
#end
#if (Obj_Switch = 1)
        #declare Object = 
                lathe  {
                        quadratic_spline
                        6, 
                        <0.0, 0.000000 >,
                        <0.00000, 0.00645 >,
                        <0.86452, 0.09677 >,
                        <0.28387, 0.35484 >,
                        <0.24516, 0.48 >,
                        <0.00000, 1.00645 >
                        scale <0.7, 0.8, 0.7>
                }
#end
#if (Obj_Switch = 2)
        #declare Object =
                bicubic_patch  {
                        type 1 flatness 0.0 u_steps 4 v_steps 3
                        < -0.6, -1, 0.5 >,      < -0.33, 0.0, 0.5 >,
< 0.33 , 0.0, 0.5 >,    < 0.5, -1, 0.6 >,
                        < -0.5, 0.0, 0.33 >,    < -0.33, -0.2, 0.33 >,
< 0.33, -0.2, 0.33 >,   < 0.5, 0.0, 0.33 >,
                        < -0.5, 0.0, -0.33 >,   < -0.33, -0.2, -0.33 >,
< 0.33, -0.2, -0.33 >,  < 0.5, 0.0, -0.33 >,
                        < -0.6, -1, -0.5 >,     < -0.33, 0.0, -0.5 >,
< 0.33, 0.0, -0.5 >,    < 0.5, -1, -0.6 >
                        translate y*0.6
                }
#end


//Top row with classic gradient
object  {
        Object
        pigment { gradient x color_map { C_Map } scale 0.5 }
        translate <-1.3, 0.4, 0.6>
}
object  {
        Object
        pigment { gradient y color_map { C_Map } scale 0.5 }
        translate <0, 0.4, 0.6>
}
object  {
        Object
        pigment { gradient z color_map { C_Map } scale 0.5 }
        translate <1.3, 0.4, 0.6>
}

//Lower row with uv_mapping
object  {
        Object
        uv_mapping
        pigment { gradient x color_map { C_Map } scale 0.5 }
        translate <-1.3, -0.6, 0>
}
object  {
        Object
        uv_mapping
        pigment { gradient y color_map { C_Map } scale 0.5 }
        translate <0, -0.6, 0>
}
object  {
        Object
        uv_mapping
        pigment { gradient z color_map { C_Map } scale 0.5 }
        translate <1.3, -0.6, 0>
}


camera {
        location < 0.0, 3, -5 >
        angle 40
        look_at < 0.0, 0.0, 0.0 >
}

light_source { <0, 50, -60> rgb 1.5 }


-- 
e-mail:sme### [at] skynetbe

http://users.skynet.be/smellenbergh

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