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It's not really a bug, just a mis-understanding. You see, the UV-mapping
implemented here simply maps the X and Y of the texture to the U and V of
the object. It takes a slice of the texture from the XY plane (Z=0) and
wraps that slice around the object.
Any slice of gradient z parallel to the XY plane will have a uniform color,
since the texture will only change in the z direction.
-Nathan
smellenbergh wrote:
>
> 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] skynet be
>
> http://users.skynet.be/smellenbergh
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