POV-Ray

In POV-Ray 3.6 (including 3.62), checker and cells patterns are off by 0.001 (1e-3) units, as can be demonstrated with this scene:

camera {
  location  <0.0, 0.0, -5.0>
  direction 1.5*z
  right     x*image_width/image_height
  look_at   <0.0, 0.0,  0.0>
}

box { <-1,-1,0>, <0,0,1> pigment { checker color rgb 1 color rgb 0 scale   0.2 translate <-0.5,-0.5,0> } finish { ambient 1 diffuse 0 } }
box { < 1, 1,0>, <0,0,1> pigment { checker color rgb 1 color rgb 0 scale   0.2 translate < 0.5, 0.5,0> } finish { ambient 1 diffuse 0 } }
box { < 1,-1,0>, <0,0,1> pigment { checker color rgb 1 color rgb 0 scale 200.0 translate < 0.5,-0.5,0> } finish { ambient 1 diffuse 0 } }
box { <-1, 1,0>, <0,0,1> pigment { checker color rgb 1 color rgb 0 scale 200.0 translate <-0.5, 0.5,0> } finish { ambient 1 diffuse 0 } }

The same can be demonstrated for the cells pattern.

POV-Ray 3.7 beta 34 is “clean”.

Bounding box computation for CSG intersection appears to be broken when one member is an arbitrarily transformed plane.

// +W640 +H480 +MB1

#include "transforms.inc"

camera {
  location  <-0.2, 0.5, -4.0>
  direction 1.5*z
  right     x*image_width/image_height
  look_at   <0.0, 0.0,  0.0>
}

sky_sphere {
  pigment {
    gradient y
    color_map {
      [0.0 rgb <0.6,0.7,1.0>]
      [0.7 rgb <0.0,0.1,0.8>]
    }
  }
}

light_source {
  <0, 0, 0>            // light's position (translated below)
  color rgb <1, 1, 1>  // light's color
  translate <-30, 30, -30>
}

plane {
  y, -1
  pigment { color rgb <0.7,0.5,0.3> }
}

intersection {
  sphere {
    0.0, 1 }
  plane { -x, 0 transform { Shear_Trans(x,y+x*0.3,z) } }
  texture {
    pigment {
      radial
      frequency 8
      color_map {
        [0.00 color rgb <1.0,0.4,0.2> ]
        [0.33 color rgb <0.2,0.4,1.0> ]
        [0.66 color rgb <0.4,1.0,0.2> ]
        [1.00 color rgb <1.0,0.4,0.2> ]
      }
    }
    finish{
      specular 0.6
    }
  }
  rotate -y*5
}

The following scene, showing an almost cylindrical cone floating above a plane, renders fine in POV 3.6.2, but is obviously broken in 3.7.0.beta.34:

camera {
  right     x
  up        y*image_height/image_width
  location  <80,50,40>
  look_at   <0,0,0>
}

light_source { <500,500,500> color rgb 1 }

cone {
  <0,0,30>, 11.303000, <0,0,-30>, 11.302999
  texture { pigment { color rgb 1 } }
}

plane { y, -20 texture { pigment { color rgb 0.3 } } }

The error occurs even with the -MB option, indicating that the problem has nothing to do with bounding, but is in the cone intersection testing code.

The attached TIFF file was created with IC using compression. When used in an image_map, POV-Ray 3.7.0.beta.34 on Windows XP x64 renders the image all transparent, while POV-Ray 3.6.2 renders the file fine. The same effect can be seen with LZW-compressed TIFF files created with Adobe Photoshop 6.0.

Uncompressed TIFF files created with either IC or Photoshop render fine in both versions of POV-Ray.

Stepping through the code of POV-Ray 3.7.0 shows that the same code path is taken regardless of compression, but the libtiff library returns different alpha channel values, indicating a problem in that library. POV-Ray 3.7 still uses libtiff 3.6.1, whereas the POV-Ray 3.6 branch has been updated to libtiff 3.8.2, which according to the change history includes a few alpha-related changes.

Source code inspection during examination of issues with the scene published at http://povray.sitewww.ch/?p=177 show the following issues with current (beta.34) implementation of dispersion in POV-Ray 3.7:

• The same adjustment to the IOR that is applied at the very first dispersion interface is erroneously applied to all subsequent interfaces.

• As an exception, dispersion adjustment is erroneously not applied to any interface defined by the surface of a non-dispersing object embedded into a dispersing object.

While this still allows to use dispersion for artistic effect, it is neither physically realistic, nor does it match 3.6 behavior.

For some particularly “heavy” SDL scripts, it might be desirable to override (or complement) the standard “Parsing 47110815K tokens” progress information with some more helpful custom info, e.g. “Planting trees... (37%)”, or “Generating terrain mesh row 47 of 500”.

The following (bogus) SDL code causes POV-Ray 3.7 beta to crash hard with an access violation:

#include "fubar.inc"
Bar(42)
#macro FooBar() #end

//fubar.inc
#macro Foo(Fnord) #end
#macro Bar(Ignord) Foo(23 #end

Input image files may have been created with gamma pre-correction for some specific target gamma, which may vary from image to image. Some file formats like PNG or HDR support embedding gamma pre-correction information in the image file, but this information may be missing or faulty, and some formats don’t support it at all. Additionally, it may be desirable to tamper with an input image’s gamma for artistic reasons.

Therefore, I suggest adding a means to explicitly specify input images’ originally intended target gamma on a per-image basis, like:

image_map { jpeg "MyImage.jpg" assumed_gamma 1.8 }

The following files were garbled in changelist #4648 by stripping all line terminators, making the files unusable:

• .../scenes/advanced/cats/cattext.inc
• .../scenes/animations/life/blink4.inc
• .../scenes/animations/life/walker.inc

Line terminators of these files were already problematic in previous versions of the file, having been CR-only.

The following files changed with #4648 should be reviewed closely as well, as they were previously CR-only, too, and at least some of them exhibit some peculiarities regarding line and/or file terminators:

• .../scenes/animations/pentmap/pentmap.ini
• .../scenes/animations/pentmap/pentmap.pov
• .../scenes/animations/slinky/slnk.ini
• .../scenes/incdemo/metals/metals.doc
• .../scenes/incdemo/stones/stones.doc
• .../scenes/incdemo/woods/morewood.doc
• .../scenes/incdemo/woods/woods.doc
• .../scenes/textures/pigments/skies/skies.doc

Subsurface scattering must be made radiosity-aware.

Adjusting the brightness of an image-mapped sky sphere, although not an uncommon task especially when using HDR light probes, currently is cumbersome at best, as it is not possible to specify a “finish { ambient ... }” statement.

To simplify tuning a sky sphere’s brightness, I suggest introducing a “brightness FLOAT” modifier (defaulting to 1.0) to either the sky_sphere block or (as a more versatile solution) the image_map statement.

Some sample scenes are no longer up-to-date, causing warnings, and should be fixed. For instance, the advanced/benchmark scene still includes “Buffer_Output=Off” and “Buffer_Size=0” in its .ini file. This should be checked systematically, and fixed as appropriate.

When rendering a series of scenes (e.g. animation, or render queue in POV-Ray for Windows), number_of_waves is not properly reset to its default value between scenes, causing the parameter to default to the value set by the previous scene.

For instance, rendering the following scenes from a queue will cause “arches.pov” to be rendered differently the second time:

1. scenes\textures\finishes\arches.pov
2. scenes\textures\normals\normavg.pov
3. scenes\textures\finishes\arches.pov (again!)

The parser does not accept mesh objects (or CSG objects including a mesh object) as a parameter to the inside() built-in function, reporting error “Solid object identifier expected”, even if the mesh is “solidified” by specifying an inside_vector.

(see news://news.povray.org:119/4a983716@news.povray.org)

Trace level is not handled properly with blobs using per-component reflective or refractive textures, leading to lockups. Stepping through the code, it seems that POV-Ray fails to properly mark the blob object as increasing the trace level.

(Until this bug is fixed, the issue can be worked around in most cases by assigning a reflective texture to the blob as a whole.)

Bounding box computation for CSG intersection appears to be broken when one member is an arbitrarily transformed plane.

POV-Ray 3.6.2 has the same problem (can’t test for 3.6.1).

// +W640 +H480 +MB1

#include "transforms.inc"

camera {
  location  <-0.2, 0.5, -4.0>
  direction 1.5*z
  right     x*image_width/image_height
  look_at   <0.0, 0.0,  0.0>
}

sky_sphere {
  pigment {
    gradient y
    color_map {
      [0.0 rgb <0.6,0.7,1.0>]
      [0.7 rgb <0.0,0.1,0.8>]
    }
  }
}

light_source {
  <0, 0, 0>            // light's position (translated below)
  color rgb <1, 1, 1>  // light's color
  translate <-30, 30, -30>
}

plane {
  y, -1
  pigment { color rgb <0.7,0.5,0.3> }
}

intersection {
  sphere {
    0.0, 1 }
  plane { -x, 0 transform { Shear_Trans(x,y+x*0.3,z) } }
  texture {
    pigment {
      radial
      frequency 8
      color_map {
        [0.00 color rgb <1.0,0.4,0.2> ]
        [0.33 color rgb <0.2,0.4,1.0> ]
        [0.66 color rgb <0.4,1.0,0.2> ]
        [1.00 color rgb <1.0,0.4,0.2> ]
      }
    }
    finish{
      specular 0.6
    }
  }
  rotate -y*5
}

In the following scene, the mesh object will always cast a fully-opaque shadow, even if the image has an alpha channel:

camera {
  location  <0.5, 1.0, -1.0>
  look_at   <0.5, 0.0,  0.5>
}

light_source { <0, 30, 0> color rgb 1 }

mesh {
    triangle { <0,0,0>, <1,0,0>, <1,0,1> uv_vectors <0,0>, <1,0>, <1,1> }
    triangle { <0,0,0>, <1,0,1>, <0,0,1> uv_vectors <0,0>, <1,1>, <0,1> }
    texture { pigment { uv_mapping image_map {png "FOOBAR.png"} } }
}

plane { y, -0.1 pigment { color rgb 1 } }

The following modification to the texture will give the expected results:

    texture { uv_mapping pigment { image_map {png "FOOBAR.png"} } }

The problem can be observed with both POV-Ray 3.7 (tested with beta.34), as well as 3.6 (tested with 3.6.2).

When aborting a render when there are unfinished blocks among finished ones, under certain conditions some of those blocks are skipped when continuing the render later.

As the following scene demonstrates, the “inverse” keyword produces unexpected results with quadrics.

Left: a sphere primitive as reference
Right: a sphere-shaped quadric primitive (sphere-shaped)

Top: plain
Bottom: inverse

The objects are clipped in half to better demonstrate the effect. Regular texture is shown in white, interior_texture in red; the surface normal of a selected point (blue) as returned by trace() is shown in green.

Note how the sphere’s surface normal, as well as the textures, are flipped when “inverse” is used (this is the intended standard behaviour of all objects), while the quadric’s normal and textures erroneously remain uchanged.

// +w800 +h600

#version 3.7;

global_settings{ assumed_gamma 1.0 }

#default{ finish { ambient 0.1 diffuse 0.9 specular 0.5 }} 

camera {
  perspective
  angle 40
  right     x*image_width/image_height
  location  <0,0,-10>
  look_at   <0,0,0>
}

light_source{ < 1000,3000,-3000> color rgb 1 }

background { color rgb 0.5 }

#declare T_White = texture { pigment { color rgb   1 } }
#declare T_Red   = texture { pigment { color red   1 } }
#declare T_Green = texture { pigment { color green 1 } }
#declare T_Blue  = texture { pigment { color blue  1 } }

#declare TopLeft     = sphere { 0, 1 }
#declare BottomLeft  = sphere { 0, 1 inverse }

#declare TopRight    = quadric { <1,1,1>, <0,0,0>, <0,0,0>, -1 }
#declare BottomRight = quadric { <1,1,1>, <0,0,0>, <0,0,0>, -1 inverse }

#macro Mac(Obj, P, D)
  union {
    #local N = <0,0,0>;
    #local O = <-0.6,0.4,-10>;
    #local Q = trace(Obj, O, D, N);
    #if (vlength(N) > 0)
      sphere { Q, 0.05 texture { T_Blue } }
      cylinder { Q, Q + N, 0.02 texture { T_Green } }
    #else
      cylinder { O, O + D*10000, 0.02 texture { T_Red } }
    #end
    object { Obj texture { T_White } interior_texture { T_Red } clipped_by { box { <-1,-1,-1>, <0,1,1> rotate y*30 } } }
    translate P
  }
#end

Mac(TopLeft,     <-1.2, 1.2, 0>, z)
Mac(TopRight,    < 1.2, 1.2, 0>, z)
Mac(BottomLeft,  <-1.2,-1.2, 0>, z)
Mac(BottomRight, < 1.2,-1.2, 0>, z)

As the following scene demonstrates, the “inverse” keyword produces unexpected results with fractals.

Left: a sphere primitive as reference
Right: a julia fractal

Top: plain
Bottom: inverse

The objects are clipped in half to better demonstrate the effect. Regular texture is shown in white, interior_texture in red; the surface normal of a selected point (blue) as returned by trace() is shown in green.

Note how the sphere’s surface normal, as well as the textures, are flipped when “inverse” is used (this is the intended standard behaviour of all objects), while the fractal’s normal and textures erroneously remain uchanged.

// +w800 +h600

#version 3.7;

global_settings{ assumed_gamma 1.0 }

#default{ finish { ambient 0.1 diffuse 0.9 specular 0.5 }} 

camera {
  perspective
  angle 40
  right     x*image_width/image_height
  location  <0,0,-10>
  look_at   <0,0,0>
}

light_source{ < 1000,3000,-3000> color rgb 1 }

background { color rgb 0.5 }

#declare T_White = texture { pigment { color rgb   1 } }
#declare T_Red   = texture { pigment { color red   1 } }
#declare T_Green = texture { pigment { color green 1 } }
#declare T_Blue  = texture { pigment { color blue  1 } }

#declare TopLeft     = sphere { 0, 1 }
#declare BottomLeft  = object { TopLeft inverse }

#declare TopRight    = julia_fractal{ <-0.083,0.0,-0.83,-0.025> quaternion sqr max_iteration 8 precision 20 scale 0.9 }
#declare BottomRight = object { TopRight inverse }

#macro Mac(Obj, P, D)
  union {
    #local N = <0,0,0>;
    #local O = <-0.6,0.4,-10>;
    #local Q = trace(Obj, O, D, N);
    #if (vlength(N) > 0)
      sphere { Q, 0.05 texture { T_Blue } }
      cylinder { Q, Q + N, 0.02 texture { T_Green } }
    #else
      cylinder { O, O + D*10000, 0.02 texture { T_Red } }
    #end
    object { Obj texture { T_White } interior_texture { T_Red } clipped_by { box { <-2,-2,-2>, <0,2,2> rotate y*30 } } }
    translate P
  }
#end

Mac(TopLeft,     <-1.2, 1.2, 0>, z)
Mac(TopRight,    < 1.2, 1.2, 0>, z)
Mac(BottomLeft,  <-1.2,-1.2, 0>, z)
Mac(BottomRight, < 1.2,-1.2, 0>, z)

The following scene demonstrates how media sampling method 3 gives inaccurate results with scattering media.

The scene shows four spheres with uniform media, using (left to right) sampling methods 1, 2 and 3 with default settings, and sampling method 3 with high minimum sample count, respectively.

Note how changing the sample count significantly affects the result, despite the media being uniform.

Code analysis shows that the root cause is an underestimation of the extinction effect on the light scattered by the media, corresponding in order of magnitude to half the distance between mandatory samples (as defined by minimum sample count).

The effect also leads to visible artifacts when nesting hollow objects inside the media, as can be demonstrated by un-commenting the four smaller spheres.

#version 3.7;

camera {
  perspective angle 25
  location  <0.0 , 0.0 ,-20.0>
  right     x*image_width/image_height
  look_at   <0.0 , 0.0 , 0.0>
}

light_source {
  <0,3000,-3000> color rgb 1
}

background { color rgb 0.5 }

plane {
  <0,1,0>, -1
  texture { pigment { checker color rgb<1,1,1>*1.2 color rgb<0.25,0.15,0.1>*0 } }
}

#declare T_Transparent = texture {
  pigment { color rgbt <1,1,1,1> } finish { diffuse 1 }
}

sphere { <-3,0,0>, 1.00 
  texture { T_Transparent }
  hollow
  interior {
    media {
      scattering { 1 color rgb 2 extinction 1 }
      method 1
    }
  }
}

sphere { <-1,0,0>, 1.00 
  texture { T_Transparent }
  hollow
  interior {
    media {
      scattering { 1 color rgb 2 extinction 1 }
      method 2
    }
  }
}

sphere { <1,0,0>, 1.00 
  texture { T_Transparent }
  hollow
  interior {
    media {
      scattering { 1 color rgb 2 extinction 1 }
      method 3
    }
  }
}

sphere { <3,0,0>, 1.00 
  texture { T_Transparent }
  hollow
  interior {
    media {
      scattering { 1 color rgb 2 extinction 1 }
      method 3
      samples 100
    }
  }
}

/*
sphere { <-3,0,0>,0.8 texture { T_Transparent } hollow }
sphere { <-1,0,0>,0.8 texture { T_Transparent } hollow }
sphere { < 1,0,0>,0.8 texture { T_Transparent } hollow }
sphere { < 3,0,0>,0.8 texture { T_Transparent } hollow }
*/

The configure script for unix uses a dumb string compare to test whether libpng version is 1.2.5 or higher, leading it to reject (for instance) libpng 1.2.27 and unnecessarily compile and statically link the older libpng version it comes with.