urp-shadergraph

name

urp-shadergraph

description

Use when authoring or editing a shader/material for Ankhora's three real visual needs on Quest 3 — translucent "ghost hands" for replay, an annotation highlight, or a spatial-anchor halo. Covers URP Shader Graph choices, mobile-VR cost, and the Unity_ManageShader/Unity_ManageAsset workflow. Triggers: shader, shader graph, material, ghost hands, translucent hands, hologram, annotation highlight, anchor halo, transparent, fresnel, emissive, URP shader.

URP Shader Graph (Ankhora)

Ankhora renders on URP 17.4.0 on a Quest 3 (mobile GPU, target 90 Hz, tile-based, fill-rate bound — see @.cursor/rules/004-vr-performance.mdc). Shaders are not a generic playground here: there are exactly three visual needs in the MVP/V1. Build for those; do not add shader complexity the masterclass does not require.

The three real needs

1. Ghost hands (replay) — the expert's recorded hands shown as a translucent, slightly emissive overlay so the learner can match pose without occluding their view.
   • Transparent surface, low alpha (~0.25–0.4), soft Fresnel rim for a "presence" read, subtle emissive tint. No refraction, no per-pixel lighting model heavier than needed. Render after opaque; watch for sorting against passthrough.
2. Annotation highlight — make an annotated object/area pop without a heavy outline.
   • Cheapest acceptable: emissive boost + Fresnel rim on the existing material, or a thin additive shell. Avoid full-screen post outline (fill-rate cost on Quest).
3. Spatial-anchor halo — a soft ground/space marker showing where an anchor sits.
   • Unlit transparent, radial gradient / soft ring, gentle pulse via Time. Unlit keeps it cheap.

Mobile-VR cost rules (non-negotiable on Quest)

• Unlit > Lit whenever you can get away with it. Most of the above can be Unlit.
• Transparency is overdraw — keep ghost hands and halos small in screen space; never stack many large transparent layers.
• No GrabPass / scene-color / refraction (expensive or unsupported on tiled mobile GPU).
• Keep texture samples and node count low; prefer math (Fresnel, gradients) over textures.
• Author single-pass instanced-safe graphs (stereo). Test in the Meta XR Simulator or on device — Mac Editor Play Mode does not render hand tracking (@CLAUDE.md).

Workflow over MCP

1. Create/edit the shader with Unity_ManageShader (or a Shader Graph asset via Unity_ManageAsset). Keep the graph small and named clearly (e.g. GhostHands_URP, AnnotationHighlight_URP, AnchorHalo_URP).
2. Create the material and assign it; wire exposed properties (alpha, rim power, emissive color, pulse speed) so they are tweakable without editing the graph.
3. Validate compilation: Unity_ReadConsole shows no shader errors; Unity_ValidateScript is for C#, so for shaders rely on console + a capture.
4. Verify visually: Unity_SceneView_Capture2DScene — confirm the transparent read is correct and not z-fighting / mis-sorted against passthrough.

Out of scope

Stylised lighting overhauls, post-processing stacks, compute/GPU-particle effects — not in the MVP. If a request heads there, flag the perf budget before building.