> [!abstract] Summary > **Custom AOVs from shading** — output any shader value (RGB masks, sub-shader contributions, LPE-like splits) as its own AOV. Useful for masking-by-shader in compositing without re-rendering. The trick: write the value to a **Render Var** sourced from a shader output, then bind it through Render Product → Render Settings. --- # RGB Mask AOV You can author **custom AOVs based on any shader value**. For example, write a per-material RGB mask in your shader, expose it via a custom output, and route it to its own AOV — Nuke can use it directly as a compositing mask without re-rendering. > [!video] Full walkthrough > [Open in Google Drive](https://drive.google.com/file/d/12anngFo-fmqezWaQVnm1kvg4n6GIygHx/view?usp=sharing) --- # General Pattern 1. **In the shader (MTLX / Arnold / RenderMan):** add an output for your custom value (an RGB mask, a sub-shader contribution, a per-material colour ID). 2. **Render Var LOP** — create a render variable that reads from your custom output. 3. **Render Product LOP** — bundle the new Render Var into a product (or merge with the beauty product). 4. **Render Settings LOP** — reference the product in Ordered Products. The custom AOV will now write to disk alongside the beauty. --- # Common Custom AOVs | AOV | What it carries | Comp use | |---|---|---| | **RGB Mask** | One colour per material/asset | Per-material grade in Nuke. | | **Per-LPE split** | Beauty per light tag | Light relight without re-rendering. | | **PRef / world position** | Reference-frame position | Project textures, masks that follow animation. | | **Custom value** | Anything authored in the shader | Procedural masks (noise, distance, edge wear). | See also [[../../../../ARTFX OSMIUM/TOOLS/Notes/Pref aov solaris (any render engine) - Loris Eck|Pref AOV Solaris]] for the reference-position case in detail. --- # 🔗 Related - [[../SOLARIS MOC|SOLARIS MOC]]. - [[../LOOKDEV HOUDINI SOLARIS|LOOKDEV HOUDINI SOLARIS]] — AOV authoring fundamentals. - [[../../KARMA/Notes/KARMA Rendersettings and AOV|KARMA — Render Settings and AOVs]]. - [[../../../../ARTFX OSMIUM/TOOLS/Notes/Pref aov solaris (any render engine) - Loris Eck|Pref AOV Solaris]] — reference-position AOV. - [[../../../../ARTFX OSMIUM/TOOLS/Notes/LPE For Emissive light - FABIO SGUERA - Houdini 20.0 HDA|LPE for Emissive Light HDA]] — LPE-style AOV splitting.