Radiosity-Pretrace 1.1 User Manual

This document explains how to use the POV-Ray SDL file radiosity-pretrace.inc, which implements some of the radiosity pretrace recomendations in Radiosity Voodoo Volume 2 in povray.text.tutorials. The main reason for creating the file was to automatically generate an ideal pretrace_start value by calculating the power of 2 by which to multiply the pretrace_end without exceeding a given maximum.

Downloaded Files

The zip archive should contain these three files:

• radiosity-pretrace.css
• radiosity-pretrace.html
• radiosity-pretrace.inc

File radiosity-pretrace.inc is the only file required for rendering; the other two are part of the documentation.

Prerequisite

Radiosity-Pretrace requires POV-Ray version 3.5 or later.

Finish ambients will work as expected for POV-Ray versions 3.5 through 3.8.

Usage

1. Include this file once prior to using the macro:

   #include "radiosity-pretrace.inc"

   Including the file more than once is harmless, though unnecessary.

2. (Optional.) To write the radiosity settings to the debug stream, set identifier Radiosity_Pretrace_debug to true before the next step:

   #declare Radiosity_Pretrace_debug = true;

3. Call Radiosity_Pretrace() from within the radiosity block. For example:

   global_settings
   { radiosity
     { count 200
       error_bound 0.5
       Radiosity_Pretrace (0.1, 1)
       recursion_limit 2
     }
   }

Macro

Radiosity_Pretrace (Max, Min)

Sets pretrace_start and pretrace_end. The arguments are:

Max:

The maximum value for pretrace_start. The actual value used may be less than this, but will always be more than half this value.

Min:

If less than 1.0, this will be used directly as the pretrace_end. If 1.0 or greater, this will be the pretrace_end value in pixels.

For the Radiosity Voodoo recommendation, pass 1 as the Min argument. However, I find that 2 is usually sufficient. If you are still using POV-Ray 3.6, a value of 0.01 is often sufficient.

Examples

Example 1

radiosity
{ Radiosity_Pretrace (0.1, 2)
}

If this is rendered at 800 by 600 pixels, Min argument 2 translates to a pretrace_end of 2/800. The largest power of 2 that will not cause pretrace_start to exceed Max argument 0.1 is 5, and (2/800) × 2⁵ = 0.08. The resulting radiosity block is:

radiosity
{ pretrace_start 0.08
  pretrace_end 0.0025
}

Example 2

radiosity
{ Radiosity_Pretrace (0.08, 0.01)
}

Since the Min argument is less than 1.0, it will be used directly as the pretrace_end. The largest power of 2 that will not cause pretrace_start to exceed Max argument 0.08 is 3, and 0.01 × 2³ = 0.08. The resulting radiosity block is:

radiosity
{ pretrace_start 0.08
  pretrace_end 0.01
}

About Radiosity-Pretrace

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