It is possible to get a nice leaded stained-glass effect using only the crackle texture and a bit of other native POV-Ray goodness.

At the moment, only this image is available at 1280×1024. The rest are at 320×240.

First, start with a simple scene to show how this works. Then, modify the portion between the bars of asterisks to redefine Stained_Glass_texture until it looks right.

The images are linked to higher resolution versions.

 1: /*stainedglass_.pov
 2: (c)2007 David Wagner
 3: */
 4: #include "colors.inc"
 5: #include "skies.inc"
 6:
 7: global_settings {assumed_gamma 2.2}
 8:
 9: camera { up z sky z
10: // Positive x is right, y is foward, z is up.
11:    location<0,-1.5,1.5> look_at <0,0,1.5>
12:    }
13: light_source{<0,0,0> color Gray80
14: // Light is coming from behind and to the right.
15:    fade_distance 200 fade_power 3
16:    looks_like {sphere {<0,0,0>1
17:       pigment {BrightGold} finish{ambient .8} }}
18:    translate <20,-30,40>
19:    }
20: sky_sphere {S_Cloud5 rotate 90*x }
21: disc{<0,-1,0>,z,10 pigment{color Gray50} finish{reflection 0.3} }
22: sphere{<0,0,0>,.1 pigment{Green} }
23: cone{<0,0,0>.03 <0,0,1>.01 pigment {White} }
24: /*
25:   Everything prior to this sets up the basic scene
26:   and will remain unchanged.
27:   ***********************************************/
28:
29: #declare Stained_Glass_texture=texture{
30:          pigment{color 0.4*Red   +Gray40 filter 1}
31:          finish{specular .8 } }
32:
33: /***********************************************
34:   The following object applies the Stained_Glass_texture
35:   to a single surface, a square section of the x/z plane.
36:   */
37: intersection{
38:    box{<0,0,0><1,1,1> pigment{Clear} }
39:    plane{y,0.001
40:       texture{Stained_Glass_texture}
41:       }
42:    translate<-1/2,0,1>
43:    }

The crackle texture creates cells about one unit in size, obviously too big for a 1-unit square. The crackle parameters shown here are this pattern's defaults.

  ***********************************************/
#declare StainedGlass_texture=texture{
         pigment{crackle form <-1,1,0> metric 2 solid
            }
         finish{specular .8}
         }
/***********************************************

I like to use irrational numbers for transformations such as this one to scale down the crackle texture.

  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare StainedGlass_texture=texture{
         pigment{crackle form <-1,1,0> metric 2 solid
            scale pow(Phi,-5) }
         finish{specular .8} }
/***********************************************

Using a linear color_map results in the colors all bunched up in the middle around green and blue.

  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare StainedGlass_texture=texture{
         pigment{crackle form <-1,1,0> metric 2 solid
            scale pow(Phi,-5) color_map{
               [0   color 0.4*Red   +Gray50 filter 1]
               [1/3 color 0.4*Green +Gray50 filter 1]
               [2/3 color 0.4*Blue  +Gray50 filter 1]
               [1   color 0.4*Red   +Gray50 filter 1]
               } }
         finish{specular .8} }
/***********************************************

Changing the crackle pattern's waveform to sine_wave seems to distribute the colors evenly.

  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare StainedGlass_texture=texture{
         pigment{crackle form <-1,1,0> metric 2 solid sine_wave
            scale pow(Phi,-5) color_map{
               [0   color 0.4*Red   +Gray50 filter 1]
               [1/3 color 0.4*Green +Gray50 filter 1]
               [2/3 color 0.4*Blue  +Gray50 filter 1]
               [1   color 0.4*Red   +Gray50 filter 1]
               } }
         finish{specular .8} }
/***********************************************

The regular (not solid) crackle has the same pattern, with values near zero (black when used as a pigment) being where the lead is between glass pieces.

  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare StainedGlass_texture=texture{         
         pigment{crackle form <-1,1,0> metric 2
            scale pow(Phi,-5)
            }
         finish{ambient .2 phong .2 diffuse .5 reflection .3 metallic }
         }
/***********************************************

Assigning separate glass and lead textures, both based on the same crackle pattern, then mapping these using this pattern yet again achieves the overall effect in two dimensions.

• Use the variable i to slice out different parts of the pattern.
• Experiment with Lead_Width to get the lead thickness you like.
• Scaling and other transformations and warps are applied indirectly in a separate macro, StainedGlass_crackle_transformed(i). This is so the transformations are only applied once.

  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare i=0;
#declare Lead_width=0.05;
 
#macro StainedGlass_crackle(i)  
       crackle form <-1,1,0> metric 2
       #end
 
#macro StainedGlass_crackle_transformed(i)  
       StainedGlass_crackle(i)
       translate i rotate ((360/Phi)*i)
       scale pow(Phi,-5)
       #end
 
#declare Glass_texture=texture{
         pigment{StainedGlass_crackle(i) solid sine_wave
            color_map{
               [0   color 0.4*Red   +Gray50 filter 1]
               [1/3 color 0.4*Green +Gray50 filter 1]
               [2/3 color 0.4*Blue  +Gray50 filter 1]
               [1   color 0.4*Red   +Gray50 filter 1]
               } }
         finish{specular .8} 
         }
#declare Lead_texture=texture{         
         pigment{StainedGlass_crackle(i)
            }
         finish{ambient .2 phong .2 diffuse .5 reflection .3 metallic }
         }
#declare StainedGlass_texture=texture{
         StainedGlass_crackle_transformed(i)
         texture_map{
            [0          Lead_texture]
            [Lead_width Lead_texture]
            [Lead_width Glass_texture]
             }   }
/***********************************************

There are a few things to note.

• Two nearly identical macros are needed, one for most uses, and one just for normals. Do not apply transformations to these.
• The first argument of StainedGlass_crackle_bump_size(_Bump_Size,i) controls the overall three-dimensional effect.
• Part of the StainedGlass_normal is used for the Lead_texture, and the rest is used for the Glass_texture.

• The turbulence warp used here makes the lead appear a bit wavier.

• The black hole warp makes it look as if larger glass pieces were used for the center and smaller pieces near the edges.

/*stainedglass_.pov
Copyright 2007 David Wagner
This software is licensed under the CC-GNU LGPL.
http://creativecommons.org/licenses/LGPL/2.1
*/
#include "colors.inc"
#include "skies.inc"
 
global_settings {assumed_gamma 2.2}
 
camera { up z sky z
// Positive x is right, y is foward, z is up.
   location<0,-1.5,1.5> look_at <0,0,1.5>
   }
light_source{<0,0,0> color Gray80
// Light is coming from behind and to the right.
   fade_distance 200 fade_power 3
   looks_like {sphere {<0,0,0>1
      pigment {BrightGold} finish{ambient .8} }}
   translate <20,-30,40>
   }                                                         
sky_sphere {S_Cloud5 rotate 90*x }
disc{<0,-1,0>,z,10 pigment{color Gray50} finish{reflection 0.3} }
sphere{<0,0,0>,.1 pigment{Green} }
cone{<0,0,0>.03 <0,0,1>.01 pigment {White} }
/*
  Everything prior to this sets up the basic scene
  and will remain unchanged.
  ***********************************************/
#declare Phi=sqrt(5)/2+.5;
#declare i=1;
#declare Lead_width=0.05;
 
#macro StainedGlass_crackle(i)  
       crackle form <-1,1,0> metric 2
       #end
 
#macro StainedGlass_crackle_bump_size(_Bump_Size,i)  
       crackle _Bump_Size form <-1,1,0> metric 2
       #end
 
#macro StainedGlass_crackle_transformed(i)  
       StainedGlass_crackle(i)
       translate i rotate ((360/Phi)*i)
       warp{turbulence pow(Phi,-4)*<1,0,1>
          octaves 3 lambda 1.5 omega 0.5}
       scale pow(Phi,-5)
       warp{black_hole <0.5,0,0.5>,1 strength -.4 }
       #end
 
#declare StainedGlass_normal=normal{
         StainedGlass_crackle_bump_size(1,i)
            slope_map {
               [0              <1    , 0>] //start flat
               [Lead_width/3   <1    , 0>] //stay flat
               [Lead_width     <0.25 ,-1>] //slope down to edge of lead
               [Lead_width+0.001<0.25 , 1>]
               [Lead_width+0.25<Lead_width+0.5, 0>]
                  //use greater final height for thicker glass
               [1              <Lead_width+0.5, 0>] 
               } }
#declare Glass_texture=texture{
         pigment{StainedGlass_crackle(i) solid sine_wave
            color_map{
               [0   color 0.4*Red   +Gray50 filter 1]
               [1/3 color 0.4*Green +Gray50 filter 1]
               [2/3 color 0.4*Blue  +Gray50 filter 1]
               [1   color 0.4*Red   +Gray50 filter 1]
               } }
         normal{average normal_map{
            [1 waves 0.10 scale pow(Phi,4)] 
            [9 StainedGlass_normal]
            } }
         finish{specular .8}
         }
#declare Lead_texture=texture{         
         pigment{Gray60}
         normal{average normal_map{
            [1 waves 0.10 scale pow(Phi,4)]
            [4 dents 2 scale pow(Phi,-4)]
            [4 wrinkles 1 scale pow(Phi,-5)]
            [4 StainedGlass_normal ]
            } }
         finish{ambient .2 diffuse .5 phong .2 reflection .3 metallic}
         }
#declare StainedGlass_texture=texture{
         StainedGlass_crackle_transformed(i)
         texture_map{
            [0          Lead_texture]
            [Lead_width Lead_texture]
            [Lead_width Glass_texture]
            } }
/***********************************************
  The following object applies the StainedGlass_texture
  to a single surface, a square section of the x/z plane.
  */
intersection{
   box{<0,0,0><1,1,1> pigment{Clear} }
   plane{y,0.001
      texture{StainedGlass_texture}
      }      
   translate<-1/2,0,1>
   }

The slice using i=0 has some large lead-filled areas. Using i=1 gives a better result.

At the moment, only this image is available at 1280×1024.

Here are a few ideas on using this texture.

• The macro and micro textures of both the leading and the glass can be improved.
• The glass finish is not convincing; try flattening it and using some reflection.
• Use facets to vary the orientation of each piece of glass.
• Depending on your lighting, the lead may be too bright or the glass too saturated. Try decreasing the Lead_texture pigment to Gray40 or so, and increase the +Gray50 components of the Glass_texture.
• Instead of a full rainbow of glass colors, use discrete, limited color ranges around the colors appropriate for your composition. You may wish to use the color ranges common to historical glass pigments.
• Adjust the glass texture to produce good fake caustics.
• When applying to a three-dimensional object (instead of a single plane), mirror it but use slightly different normals on front and back. Then see how well it works with photons.
• Repeat and randomize the black hole warp for large sheets of stained glass.
• See what happens with strong black hole warps, both positive and negative. (There are some nice effects.)
• Try to make a rose window effect by combining crackle and radial textures. Please let me know how you do it.
• Extend this technique for making broken and rounded glass pebble mosaics, fruitcakes, and other things.
• Try to remove the dependency on that i value.
• Scale the pattern normal to the surface to reduce large lead fills.

And, please don't forget to share your experience.

Although this technique is mentioned in the manual, I could not find a good reference for using only textures to create a reasonable stained-glass effect. At first I used a height_field to make the lead, similar to the isosurface technique used in this competition entry, POVCOMP 2004: Viewing Page for "A Bat in the Belfry". Although the height_field technique works fine, it is a pain to keep everything aligned correctly. I wanted to simplify the usage of this effect and to minimize its render time so it can be used in animation.

I think I succeeded.

— David Wagner 2007/01/21 13:51