OSL in 3Delight

General Guidelines

3Delight supports all the required functions to properly run OSL shaders. That being said, the philosophy of writing OSL shaders for 3Delight differs very slightly from other renderers. In a nutshell,  the 3Delight rendering core is organized so that OSL shaders can remain as abstract as possible. For example, it is discouraged (and indeed wrong) to use functions such as backfacing() to write shaders. Also, some shadeops have seen their definition slightly changed to simplify shader writing or to allow 3Delight make a better job at sampling the final image. 

Consider the following simplified "glass" shader and compare it to the "glass" shader distributed with OSL:

surface glass
    [[ string help = "Simple dielectric material" ]]
(
    float Ks = 1,
    color Cs = 1,
    float eta = 1.5
  )
{
    Ci = Ks * reflection(N, eta) + Cs * refraction(N, eta);
}

surface glass
    [[ string help = "Simple dielectric material" ]]
(
    float Ks = 1,
    color Cs = 1,
    float eta = 1.5
  )
{
	float _eta = backfacing() ? 1/eta : eta;
	Ci = Ks * reflection(N, _eta) + Cs * refraction(N, _eta);
}

As you can see, there are no fresnel terms and no backfacing() call. 3Delight will take the proper decision, based on many factors including the fresnel factors, to properly sample the surface. 

Supported Closures

3Delight supports all the most advanced closures. Some of the BRDF went through extensive research in order to extend them beyond the original specs. As an example, 3Delight's GTR can also model refractions, allowing to render realistic forested glass and other effects.

Unified Budgeted Sampling

For the first time, a renderer provides only one sampling control for all the lighting components: specular, diffuse and light. By adjusting only one "Shading Samples" value, the artist can reduce noise without having to fiddle around with per-material or per-component sampling. 3Delight uses space varying heuristics to select the best element to sample (specular, diffuse, light) by respecting the total allotted rays budget.

For the anti-aliasing component, 3Delight provides a non-multiplicative "PixelSamples" control. This control is detached from the "Shading Samples" parameter so that artists can control shading quality and anti-aliasing quality independently.

The following simple renders illustre how "Shading Samples" control the various lighting elements all at once. The scene is mostly matte (diffuse) with a GGX material applied to the tall cube.

	AA=2x2, Shading Samples = 16	AA=2x2, Shading Samples = 64	AA=2x2, Shading Samples 256	AA=4x4, Shading Samples 256
Number of Rays	12.7 millions	48.7 millions	191 millions	194 millions
Time	6.5 seconds	26.5 seconds	100 seconds	108 seconds
Remarks	Draft render	Notice how diffuse, specular and shadows improve together.	High quality render with linear improvement among all lighting elements.	Increasing pixel samples do not affect render time since all the time is spent in shading.

A very important feature of the Unified Budget Sampling is that sampling quality is independent of the number of lights. Consider the following two renders. One is done using 3Delight the other is using PrMan.