POV-Ray

A low priority thought for the future: isosurface now only allows contained_by to be a sphere or a box. It would be more intuitive to allow the same objects that are allowed in clipped_by and bounded_by (although it probably needs to be finite). It would enable allow much faster rendering in many cases:

1) There are a lot of cases when the sphere or a box are very bad in bounding - if an object has a hole, a torus may be better, and in many cases, cylindrical bounding would help a lot.
2) Sometimes, having a too large contained_by object includes far-away parts of the iso-function, and expose large gradients that you want to avoid. If a bounding object is better, you can decrease the max_gradient and speed up the render.
3) The isosurface is usually much more expensive to calculate than any normal bounding object, so it’s an improvement even if the intesection test is not as fast as bounding box.
4) A typical case: if you use texture-like functions to make the surface realistically rough, you know almost exactly what the bounding object is - it can be the original unmodified object.
5) For isosurface terrains, a preprocessing macro could create a rough mesh-like bounding object to contain the “mountains”, thus making everything faster.
6) In case you want clipping, having the contained_by set to the same object probably avoits calculating too many intersections.

The main modification is probably that the intersections of bounding objects can be split into more than one interval - but it’s probably worth it, the isosurfaces are usually a speed bottleneck.

Some features are optional in custom builds of POV-Ray (I’m thinking about OpenEXR in particular); it would be nice to have a syntax for an SDL script to check for support of such features, so it may take some fallback action if the feature is not supported.

The so-called shadow line artifact (http://wiki.povray.org/content/Knowledgebase:The_Shadow_Line_Artifact) which affects objects with a ‘normal’ statement as well as smooth meshes and heightfields can be really annoying sometimes. Currently the only way to remove it is to make the object shadowless, which isn’t a good solution except in very special cases.

This algorithm could remove the artifact: If the actual normal vector of the object points away from the light source (its dot-product with the light vector is negative) but the perturbed normal points towards it (dot-product positive), then ignore the first shadow-test intersection with the object itself.

There are alternative ways of implementing an equivalent functionality:

- Don’t check the condition (if it’s too difficult to check due to how the code is designed) but always ignore the first intersection with the objects itself. This will work properly with closed surfaces but not with open ones, so it might need to be a feature for the user to turn on with a keyword (similar to eg. ‘double_illuminate’).

- Alternatively, don’t ignore the first intersection, but instead ignore the “opposite side” of the object’s surface (again, possibly only if a keyword has been specified). In other words, if we are rendering the outer side of the object, ignore its inner side when shadow-testing, and vice-versa.

- Perhaps simply add a feature to make surfaces one-sided (similarly to how they can be made so in OpenGL and similar scanline rendering systems). In other words, the inner side of a surface is completely ignored everywhere, making the object virtually invisible from the inside. The advantage of this feature would be that it can have uses other than simply removing the shadow line artifact.

Adding full texture statement support to the background statement (with a scale of 1/1) aligned with the image_map direction of an image would allow i.e. specifying an image as background easily.

Being able to have functions operate on vectors would be pretty nice to have.

The current 32-bit linear congruential generator used as RNG in POV-Ray is sometimes quite limited for some purposes and in a few cases its poor quality shows up (as has been demonstrated more than once in the newsgroup). Thus it would be nice if POV-Ray offered additional, higher-quality random number generators, besides the current one (which should probably remain for backwards compatibility). These RNGs could include algorithms like the Mersenne Twister and the ISAAC RNG, both of which have very decent quality and have an enormous periods (while at the same time being very fast).

After a long discussion, the following syntax for specifying the RNG type and seed (which may be larger than 32 bits) has been suggested:

seed(<value>) | seed(<type>, <value> [, <values>])

For example:

#declare Seed1 = seed(123); // Use the current RNG, with seed 123
#declare Seed2 = seed(1, 123); // Identical to the previous one
#declare Seed3 = seed(2, 456, 789, 123); // Use RNG algorithm #2,
                                         // with a large seed (96 bits specified here)

A C++ implementation of the ISAAC RNG can be found at http://warp.povusers.org/IsaacRand.zip

The following scene gives a comparison of current conserve_energy handling in standard shadow computations vs. photons.

Note how the rather highly reflective slabs fail to cast shadows, except where the photons target sphere enforces computation of shadow brightness to be done by the photons algorithm.

For more realistic shadowing without the need to enable photons, I suggest do add proper conserve_energy handling to the shadow computation code (which shouldn’t be too much effort).

global_settings {
  max_trace_level 10
  photons { spacing 0.003 media 10 }
}

camera {
  right x*image_width/image_height
  location  <-2,2.6,-10>
  look_at   <0,0.75,0>
}

light_source {
  <500,300,150>
  color rgb 1.3
  photons {
    refraction on
    reflection on
  }
}

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>]
    }
  }
}

plane {
  y, 0
  texture { pigment { color rgb 0.7 } }
}

#declare M_Glass=
material {
  texture {
    pigment {rgbt 1}
    finish {
      ambient 0.0
      diffuse 0
      specular 0.2 // just to give a hint where the sphere is
    }
  }
  interior { ior 1.0 }
}

#declare M_PseudoGlass=
material {
  texture {
    pigment {rgbt 1}
    finish {
      ambient 0.0
      diffuse 0.5
      specular 0.6
      roughness 0.005
      reflection { 0.3, 1.0 fresnel on }
      conserve_energy
    }
  }
  interior { ior 1.5 }
}


sphere {
  <1.1,1,-1.3>, 1
  material { M_Glass }
  photons {
    target 1.0
    refraction on
    reflection on
  }
}

// behind target object
box {
  <-0.2,0,-2.3>, <0.0,4,0.3>
  material { M_PseudoGlass }
  rotate z*1 // just to better see the reflection of the horizon
}

// before target object
box {
  <2.4,0,-2.3>, <2.6,4,-0.3>
  material { M_PseudoGlass }
  photons { pass_through }
  rotate z*1 // just to better see the reflection of the horizon
}

When you instantiate an object several times, eg:

object { MyObj translate -x*10 }
object { MyObj translate x*10 }

POV-Ray will copy that object in memory, at least for most types of objects. Not for all of them, though. Most famously if MyObj is a mesh, it won’t be copied, but only a reference to the original will be used, thus saving memory. (There are a few other primitives which also don’t cause a copy, such as bicubic_patch and blob, but those are naturally not so popular as mesh, so it’s a less known fact.)

AFAIK the reason why referencing (rather than copying) is not used for all types of objects is rather complicated, and mostly related to how transformations are applied to these objects. For example if the object being instantiated is a union, the translates above will be (AFAIK) applied to the individual members of the union rather than to the union object itself.

Copying, however, can be quite detrimental in some situations. For example if you have a huge union, and you want to instantiate it many times, the memory usage will be that many times larger (compared to just one instance). This is sometimes something which the user would not want, even if it made the rendering slightly slower as a consequence. (In other words, better to be able to render the scene in the first place, rather than running out of memory.)

Redesigning POV-Ray so that all objects would be referenced rather than copied would probably be a huge job, and in some cases a questionable one. There probably are situations where the current method really produces faster rendering times, so redesigning POV-Ray so that it would always reference instead of copy, could make some scenes render slower.

So this got me thinking about an alternative approach: How hard would it be to create a special object which sole purpose is to act as a reference to another object, without copying it? This special reference object would act as any regular object, would have its own transformation matrix and all that data related to objects, but its sole purpose is to simply be a “wrapper” which references an existing object. It could be, for example, like this:

object_ref { MyObj translate -x*10 }
object_ref { MyObj translate x*10 }

The end result would be exactly identical as earlier, but the difference is that now MyObj behaves in the same way as a mesh (in the sense that it’s not instantiated twice, but only once, even though it appears twice in the scene), regardless of what MyObj is.

In some cases this might render slightly slower than the first version (because POV-Ray has to apply the transformations of the object_ref first, after which it applies whatever transformations are inside MyObj), but that’s not the point here. The point is to save memory if MyObj is large.

An object_ref would behave like any other object, so you could do things like:

#declare MyObjRef = object_ref { MyObj };

object { MyObjRef translate -x*10 }
object { MyObjRef translate x*10 }

(The only thing being instantiated (and copied) here is the “MyObjRef” object, not the object it’s referring to, so that actual object is still stored in memory only once.)

In some situations it might even be so that referenced objects actually render faster than if the objects were copied because references increase data locality, lessening cache misses.

I believe this could be a rather useful feature and should be seriously considered, unless there are some major obstacles in implementing it.

When working with predefined materials, it would be useful to have something like:

#if (!Use_photons)
  #default { interior { caustics 1 } }
#end

#include "my_predefined_materials.inc"

Default medias or IORs could also be useful.

See Notepad++ or EditPad Lite for examples.

It would be nice to be able to drag tabs in the editor window to change their order, so as to group opened files together by relevance for instance.

Povray 3.7 has rendering artifact in meshes with polygons that meet at shallow angles. Please see the attached file.

The part of concern is the mesh2, which produces the partly-transparent faces of a shallow pyramid. The file result-3_6.png shows the output of povray-3.6, and the file result-3_7.png shows the output of povray-3.7. In 3.7, you can see a thin light-colored margin all around the base of the pyramid, especially thick under the top cylinder. In 3.6, this artifact is absent. For comparison purposes, I have inserted a “#version 3.6;” directive at the top of the file so that the output images are as close to each other as possible. However, the artifact is still present in 3.7 without this directive.

The attached scene file is only a small part of a much larger scene, where this artifact shows up in numerous very obvious places, where it doesn’t in 3.6. I have hunted in the documentation and online for ways to solve this problem, but haven’t found anything. Because of this, I am forced to stay with 3.6 for production use, which is quite unfortunate since I’d like to take advantage of the new features of 3.7.

The #debug message stream is only being flushed when it hits a newline character,
instead of after each #debug statement. This means that some final strings don’t show up.

#debug "This line prints,\n but this line doesn't."

Would be great if there were a “Rename” option in the editor File menu to rename the current file name. Otherwise, you have to close the file, rename it in file manager, then open the file again, thus loosing the current tab position and undo history for the file.

Would be great to have a “Reload” option in the File menu to manually reload the current file from disk, discarding all subsequent changes since the last save.

I created an INI file which specifies the Input_File_Name, Output_File_Name, and also the Render_File and the remaining four text outputs as double-quoted absolute paths on my disk. When I run the render, I get the following output:

Preset INI file is ‘C:\USERS\TPREAL\DOCUMENTS\POV-RAY\V3.7\INI\QUICKRES.INI’, section is ‘[512×384, No AA]’.
Preset source file is ‘D:\Ruby\POV-Rb\ini\20110521_004037_Noix.ini’.
Rendering with 2 threads.
-
Cannot open file.
Render failed
-
CPU time used: kernel 0.06 seconds, user 0.02 seconds, total 0.08 seconds.
Elapsed time 0.52 seconds.

And the render does not start. The five text output files are not even created, and where the output image should be, there is a file with extension pov-state. The render works as it should only when I remove all five lines defining the five text output files. The paths I specify for the files are correct (paths exist and files do not, no white-spaces or anything), read/write restrictions are disabled in POV-Ray. This used to work in 3.6 and does not work now in 3.7 RC3. The error happens no matter if I run the render using GUI or command line.

(Also please note that the error message is really not useful here, it does not say which file it failed to open, and not even if it was an attempt to open for read or for write.)

I’d be really glad if you could correct this as it’s a critical functionality for me. I’m generating the POV-Ray code automatically and I need to parse the text output automatically to return the status to the generator.