hShadertoy

Experimental Shadertoy.com importer for Houdini 21 Copernicus

https://youtu.be/ULpn8tGFsRI

Project Overview

“You know what would be cool, if you could import a Shadertoy shader to Houdini COPs, do you think it’s possible?”

1. Editor Shadertoy Mini IDE. input/output shadertoyAPI JSON.
2. Builder Sets hShadertoy HDA parameters and uses the transpiler to set OpenCL code.
3. Transpiler Translates GLSL to OpenCL - madness! never been done!

Shadertoy features implementation in Houdini Digital Asset (HDA)

• GLSL fragment shaders by OpenCL nodes
• Buffer shaders by Block Begin/Block End
• Cubemaps and Volumes packed and unpacked to 2D image maps
• iMouse by hou.ViewerState or CHOPs Mouse or SOP Draw curves (todo)
• Webcam by Live Video Copernicus node (todo)
• Audio by CHOP Audio in (todo)

Installation

1. Download and unpack hShadertoy to a local directory (eg: C:/dev/hShadertoy )

2. Install tree-sitter:

   pip install tree-sitter

3. Install tree-sitter-glsl:

   pip install tree-sitter-glsl

4. Copy houdini/packages/hShadertoy.json to your package directory (eg $HOUDINI_USER_PREF_DIR/packages )

5. Configure hShadertoy.json and set the following 3 env variables:

    { "HSHADERTOY_ROOT": "C:/dev/hShadertoy" },
    { "HSHADERTOY_HOUDINI": "C:/dev/hShadertoy/houdini" },
    { "SHADERTOY_API_KEY": "YOUR_API_KEY"},
   

   Get your API key: https://www.shadertoy.com/howto

   Note: Shadertoy API is currently blocked. Importing shaderts using API is not working.

6. Open Editor in hShadertoy shelf

Known limitations

• Shadertoy global uniforms (iChannel#, iTime.. ) used outside mainImage() will be transpiled as undefined variables and produce incomplete shader
• dFdx(), dFdy() and fwidth() are just passthrough functions. (not supported in OpenCL)
• fragColor and fragCoord are expected in mainImage(). Custom names will fail. This will be fixed at some point in near future. Prob needs a simple RegEx parsing in transpile_glsl.py

Development

Required

tree-sitter>=0.25.0
tree-sitter-glsl>=0.2.0
numpy>=2.3.0
pytest>=8.4.0
pytest-cov>=7.0.0
black>=24.0.0
pylint>=3.0.0
pyopencl>=2025.2

Pipeline

1. houdini/toolbar/hShadertoy.shelf
2. houdini/scripts/python/hshadertoy/gui/editor.py
3. houdini/scripts/python/hshadertoy/builder/builder.py
4. houdini/scripts/python/hshadertoy/transpiler/transpile_glsl.py
5. src/glsl_to_opencl
6. houdini/otls/hShadertoy.hda - hShadertoy::shadertoy
7. magic!

GLSL to OpenCL specification:

• src/glsl_to_opencl/GLSL_TO_OPENCL_SPEC.md

Unit Tests

• Location: tests/unit/
• Coverage: All transformation features
• Run: python -m pytest tests/unit/ -v

Full Transpilation Test

• python tests/transpile.py tests/../<file>.glsl
• outputs <file>.header.cl and <file>.kernel.cl for compilecl.py

OpenCL Compilation Test

• Location: tests/shaders/
• Configure: tests/build_options.json   You can extract full list of build options by setting HOUDINI_OCL_REPORT_BUILD_LOGS = 2 in houdini.env. hShadertoy HDA OpenCL node will log build options specific to your environment (more info: https://www.sidefx.com/docs/houdini/ref/env.html)
• Run: python tests/compilecl.py --header <file>.header.cl <file>.kernel.cl

Known BUGS

• matrix operations not fully covered
• all matrix functions and operations are still in dev and prone to fail.
• void() functions still need polishing (foo.x needs to become foo[0] etc)

TODO

Transpiler:

• matrix operations attribute overload
• fix void() bugs
• investigate c++ for opencl (matrix operator overload)
• texture() functions and helper runtime update (volumes, sound etc)

Builder

• fix video/volume parameter mapping mismatch

HDA

• Optimize! currently evaluates the full graph even if buffer shaders are not used. Just needs simple switch.
• Pack remaining cubemaps (use included HDA hShadertoy::cubemappack)
• Pack volumes. Similar packing to cubemaps, pack z slices into 2D image grid layout.