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Week 3

Hi everyone! Yet another week's now gone. This is my report.

Objectives

We're still in Weeks 4-5:

• Test shader functionality. If working, release test build.
• Evaluate received feedback. Start bug fixes.

What's been done

This week's been MUCH better!

• It turns out that I had WITH_CYCLES_DEBUG on, that was the source of all the NaN noise in my side. I rebuilt Blender from the ground up; I still have RelWithDebInfo on.
• Thanks to Lukas, bzztploink and artok, we could get test builds for all platforms! This enabled us to find some issues regarding:
  • Linux compilation
  • Missing initialization code
  • Some stuff I didn't know about Cycles's innards

In terms of commits,

• Me:
  • Ronan Ducluzeau's noisy renders were caused by an mistake in Lukas's optimization of the trimmed logistic distribution. It's now fixed (rB2af62e27e2c894217b5d7daa880434447ea6ed35).
  • Split off the azimuthal and longitudinal roughness factors to make debugging easier when needed (rB4a73f5ce584f49c68b2c64c74ef30188395088de).
  • Added compatibility with OpenCL. Thanks to nirved for the patches and comments! (rB9d6333127623ebed7a275d382e63da1f87712aae, rB00d0f3c23527b047f3211fd760080fdfcec4037b)
  • Added OSL compatibility. I know I don't allocate the memory for the closures correctly, I'll patch it in the weekend. (rB718d730bb409322dd9078273bfc0dc16b956a8d6, rB718d730bb409322dd9078273bfc0dc16b956a8d6, rB4774e906e19816b720c20271b9f9db28bb89debe, rBb7a92fa75e56c2b76968e523892bfb7ee9a6f19e, rBdf0ead4dabd0c0f07ff046b59c7d850005d59e60, rBbf5a378c3c350384f18ce7daf6624ef0c56ab5ba)
  • Added the final missing feature from Chiang's formulation, the R-mode roughness modifier (formally called "Primary Reflection Roughness Modifier"). It enables the user to render a shiny coat on an otherwise rough patch of fur (rB25677d7738530d8f827e5ac960ccded6b128d897, rBc3048b5f53aaeb5b860bf1760a7f1ef51f6c4701, rBb3ebdf64459d7a99e9a848a49f7eaa250b8a07bd).
    • I had to move the geometry data out of the main ShaderClosure to make space for this. I didn't know that I had to tell Blender how many closures I was using 😅, so all Final Renders returned black hair. This was found by YAFU on BlenderArtists and fixed by Brecht.
  • Enabled Filter Glossy for the roughness coefficients. Brecht reports a ~75% improvement in render quality! (rB8087cefd03022759250f5d62eb4776fa6c55be4c, rBdf1e50fa5d913d2a577a178d3f26f573795997ad)
  • Finally found out why Blender didn't listen to RNA's default for the hair parameterization. I added the correct initialization code (rB7780d306a416e0dcc37932698e70595bce58ea5e).
  • Merged the latest master commits. Only a single conflict! (Week 2: rB82e63de2842c2af8be5ec19a00752b110dbd0c57, Week 3: rBfede34a58a8df630bb927ab9c017ab2cd87478b4)
  • Bonus:
    • Turned off the Diffuse override. It doesn't seem to be needed after Brecht's curve_core_intersect patch (rB718d730bb409322dd9078273bfc0dc16b956a8d6).
    • Added our shader to the Glossy closure checker as well (rB25677d7738530d8f827e5ac960ccded6b128d897).
• Brecht:
  • Fixed the hair offset calculation by avoiding curve_core_intersect & pals altogether (rBabfca9375c6ae75320b7538d547545350ad47c85, rBff6883fbc330c5ac1333beaf38142d6b1d7728cf, rBbaad410a5c5b15158b06d9b9a9d9c86522261cea).
  • Added a few comments wrt. hair attenuation terms and offset angles (rBfc62d5a3b3622efa69a02377bc15ab6f6f1e389c).
  • Fixed the range for the R-mode roughness modifier (rB3c56635da9579a297f3b32ce2cc0b9468d308199).
  • Fixed the number-of-closures issue that came with the R-mode roughness modifier (rB1fac3b7da05ada27d8a41c114283394b5a505ebb).

Here are some images:

A R-mode-modified fur ball, also filtered with Filter Glossy. Rendered with Cuda on Win7 x64 in ~5min.

The node's current appearance and sockets.

Next up

Apart from finally settling the memory allocation flow for the OSL shader, the original shader is mostly done. I could address some of the proposed features in the BlenderArtists thread:

• Define separately the eumelanin/pheomelanin coefficients, à la Arnold's Standard Hair
• Perhaps add more features, such as tinting? Again, following Arnold's shader features.

If no more bugs arise, I may start with the rest of the objectives too.

Questions

None this time!