Syoyo Fujita 274e6826e4 Add OpenPBR parameters reference and HDRGen environment map generator tool ...

This commit adds comprehensive OpenPBR documentation and a powerful synthetic
environment map generation tool for testing and visualization workflows.

## OpenPBR Parameters Reference (doc/openpbr-parameters-reference.md)

- Complete mapping of all 38 OpenPBR parameters
- Blender v4.5+ MaterialX export parameter names
- Three.js MeshPhysicalMaterial support status with detailed notes
- Parameter categories: base, specular, transmission, subsurface, sheen, coat,
  emission, and geometry
- Support summary: 15 fully supported (39%), 7 partial (18%), 16 not supported (42%)
- Critical limitations clearly marked (subsurface, transmission effects, advanced coat)
- Conversion recommendations for Three.js WebGL target
- Blender MaterialX and USD format examples
- 8KB comprehensive reference with all technical details

## HDRGen Tool (tools/hdrgen/)

Pure Node.js synthetic HDR/EXR/LDR environment map generator with zero dependencies.

### Version 1.0.0 Features:
- Three presets: white-furnace (testing), sun-sky (outdoor), studio (3-point lighting)
- Dual projections: lat-long and cubemap (6 faces)
- HDR output: Radiance RGBE format with proper encoding
- Procedural generation: Hosek-Wilkie sky approximation, studio lighting model
- Comprehensive CLI with preset-specific options
- Full test suite: 8 unit tests, all passing
- Documentation: 15KB README, quick start guide, examples

### Version 1.1.0 Features (added in this commit):
- Image rotation: rotate environment maps around Y axis with bilinear filtering
- Intensity scaling: global brightness multiplier for testing and adjustment
- LDR output formats: PNG (8-bit RGB), BMP (24-bit), JPEG placeholder
- Tone mapping: three operators (simple, Reinhard, ACES filmic)
- Exposure control: EV-based exposure adjustment
- Gamma correction: configurable gamma for different displays

### Code Statistics:
- Total: ~1,500 lines of pure JavaScript
- Core library: 913 lines (hdrgen.js)
- CLI: 254 lines (cli.js)
- Tests: 194 lines
- Zero external dependencies

### Technical Implementation:
- HDR: Proper RGBE encoding with 8-bit mantissa + shared exponent
- PNG: Uncompressed RGB with CRC32 validation
- BMP: 24-bit RGB with proper padding
- Tone mapping: Reinhard, ACES filmic, simple clamp operators
- Image transforms: Bilinear filtering for rotation
- Math utilities: Vec3, coordinate conversions, color space operations

### Output Examples Included:
- test_furnace.hdr (white furnace for energy conservation testing)
- test_sunsky.hdr (procedural sky with sun disk)
- test_studio.hdr (3-point studio lighting)
- test_cube_*.hdr (cubemap faces, 6 files)
- studio_test.png (LDR preview with tone mapping)
- sky_test.bmp (BMP format example)

### Use Cases:
- Material energy conservation validation (white furnace)
- IBL testing and debugging
- Web-friendly environment map previews (LDR output)
- Lighting direction adjustment (rotation)
- Brightness testing (intensity scaling)
- DCC integration (Blender, Houdini, Maya, Unreal, Unity)

## Documentation Updates (doc/materialx.md)

- Added "Related Documentation" section linking to OpenPBR parameters reference
- Cross-reference for developers working with OpenPBR materials
- Better discoverability of comprehensive parameter mappings

## Testing

All functionality tested and verified:
- HDR output: Valid Radiance RGBE format
- PNG output: Valid PNG with correct CRC32
- BMP output: Valid 24-bit bitmap
- Rotation: Smooth 90° rotation with bilinear filtering
- Intensity scaling: Correct 0.5x and 2.0x multipliers
- Tone mapping: All three methods produce correct output

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

2025-11-06 02:18:48 +09:00

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