Scenario Unity Shaders

Unity shaders (technical artist, shading)

Expert shading in Unity 6.3 is a shader you can prove: it compiles for the target graphics API, every pass agrees, its variants are counted after stripping, its first use is shown warm, its cost is measured in GPU milliseconds, and its look is checked in a capture with numbers. An agent without a mouse gets there through text: hand-written URP HLSL is the primary route, Shader Graph is used through existing graphs driven by exposed properties plus agent-owned .hlsl behind Custom Function nodes, and new graph wiring is a GUI step (references/gui-paths.md). Target: 6000.3.21f1, URP 17.3, Shader Graph 17.3, Metal on Apple Silicon. If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-unity-expert (channels, review loop, 6.3 traps). Its toolkit (ut_env, ut_run, ut_review, AgentKit) is imported, never copied.

Status (2026-09-24, after the blind-grade refactor): every procedure ran in Unity 6000.3.21f1 here: tests/code/unity-shaders/run_all.sh --live (73 live checks including a development-player PSO proof, 32 offline checks, all passing; evidence in archive/tests/unity-shaders/).

Stance (the expert delta)

1. Text first, graphs by template. Shader Graph has no loops and almost no lighting nodes, so lights and loops live in HLSL (Daniel Ilett, F8bAI6dIrto [00:07:13]); its one advantage is generated depth and shadow passes (bH--RU6qyTw [00:38:24]), which AgentPasses.hlsl gives hand-written shaders too. With graphs, duplicate one, set its exposed references, put changing logic in a File-mode .hlsl. Graph Settings bind every pass: Alpha Clipping without Allow Material Override writes #define _ALPHATEST_ON 1 into all 8 generated passes, and no Boolean keyword removes it (installed UniversalTarget.cs, observed).
2. Every pass must agree. Displacement and clip() run in ShadowCaster, DepthOnly and DepthNormals too (6.3 Manual; Ilett [00:37:52]). A missing DepthOnly pass makes an opaque shader invisible with Depth Priming (observed). DepthNormals writes the raw world normal: the Manual's normal * 0.5 + 0.5 example reads back wrong in SSAO and outlines (observed).
3. Read the installed pipeline, not the tutorial. Copy keywords from the installed Lit.shader (Ilett [00:14:51]; ut_shaders.urp_lit_keywords()): 6.3 has _CLUSTER_LIGHT_LOOP and four soft shadow variants. LIGHT_LOOP_BEGIN skips directional lights, so a custom loop needs a directional pre-loop under Forward+; Unity's own Custom Lighting sample lacks it (observed).
4. Variants are a budget counted after stripping. shader_feature for material toggles, multi_compile only for runtime C# toggles, dynamic_branch tested with if, never #if (6.3 Manual). Strict Shader Variant Matching before stripping, then the funnel in the build log (Carotenuto, Unity blog 2024). A shader_feature (or _local) variant ships only if a material in the build enables it (observed 0 vs 6): never toggle one from runtime C#. Unity 6 Shader Build Settings exclude or retype keywords with zero code, but a dynamic_branch override is silently ignored for #if-tested keywords, URP's soft shadow and SSAO sets included (observed).
5. First use is proven warm. Trace one GraphicsStateCollection per graphics API and platform in a development player, warm it behind the loading screen, and show gameplay frames with zero Shader.CreateGPUProgram samples and zero logged uploads (6.3 Manual; observed 14 to 0 on Metal).
6. Cost is GPU time, not instruction count. Loops count at max trip, float4 costs about 4x float, transcendentals cost many cycles (Ben Cloward, E82XxlXMJs4 [00:15:44]). Measured here: 64 sin on a float4 about 3x a float, 10x or more a multiply-add loop. Half pays only where a device profiler shows ALU-bound (Freya Holmér, kfM-yu0iQBk [01:20:26]): desktop PlatformDefault compiles half as float.
7. Render Graph shape. RecordRenderGraph declares, never records; blit once into a new texture then resourceData.cameraColor = destination; gate in AddRenderPasses; refuse the back buffer (6.3 docs; Unity dither sample, U8PygjYAF7A [00:09:06] [00:10:10]).
8. One scalar field, one threshold, two colors; look and measure. Toon, water, dissolve, outline and dither threshold a 0..1 value (visual digest); the water's depth mask also calms its shore normals (gRq-IdShxpU [00:06:12]). Offset an emissive edge from the clip test (Brackeys, taMp1g1pBeE [00:05:31]). Output intermediates as colors (Freya [01:57:25]), then assert pixels at projected probes.

Establish first

• Platforms and graphics APIs: Metal, Vulkan, DX12, GLES 3.x, WebGL 2 or WebGPU. Compute runs on Metal, Vulkan, DX11/12 and GLES 3.1+ (4 buffers guaranteed on GLES 3.1), not on GLES 3.0 or WebGL 2; the Web gets it through WebGPU (experimental in 6.3). The GPU Resident Drawer and STP exclude GLES entirely.
• Rendering path per renderer (Forward, Forward+, Deferred+): decides the light-loop code; Shader Graph custom lighting works in Forward and Forward+ only.
• URP assets per quality level: Depth and Opaque Texture, soft shadows, SSAO. The template's Mobile_RPAsset has Depth Texture off: depth-faded water needs it on or a baked shore mask.
• Style and authors: toon or PBR; artists editing graphs (keep a graph, agent owns the .hlsl) or code only.
• Per-object values: material instance, MeshRenderer/SkinnedMeshRenderer.SetShaderUserValue (6.3, SRP Batcher friendly), or MaterialPropertyBlock (breaks the SRP Batcher).
• Budgets: GPU ms for the effect, variants per shader, overdraw, first-use hitches. Defaults when silent: URP 17.3 Forward+, PC and mobile tiers from the template, HLSL, shaders under Assets/AgentShaders/.

Workflow

1. Install and inventory. ut_shaders.install(P); RendererFeatureJobs.ListFeatures (every quality level, asset, renderer, feature); lint_shader_file, shadergraph_summary (targets, properties, Graph Settings findings), lint_project_keywords. GATE: pipeline facts in the plan; lint errors listed.
2. Author. Start from scripts/Shaders/: AgentLit, AgentToon, AgentWater, AgentDissolve, AgentEdgeOutline, AgentGrayscale, AgentCompute, shared AgentPasses.hlsl (AGENT_CLIP/AGENT_DISPLACE) and AgentNoise.hlsl. Graph route: ShaderGraphJobs.ImportPackageSample, DuplicateGraph, shadergraph_set_target_settings, GeneratedCode, AgentCustomLighting.hlsl. GATE: lint zero errors.
3. Compile for the target. ShaderJobs.ValidateShaders (ShaderUtil.GetShaderMessages plus CompileVariant per pass for Metal). GATE: zero errors, the four opaque passes present.
4. Bench and look. SetupMaterials, ShaderLab.BuildScene, ShaderLab.Shots (many shots per boot: material, renderer, feature and URP changes; probes projected to pixels). GATE: ut_review flags clean, contact sheet opened, probe numbers (shadow darker than open ground, dissolve shadow gone at 1, extra lights change the lit side).
5. Full-screen effects. RendererFeatureJobs.AddFeature with AgentFullscreenFeature or the zero-code FullScreenPassRendererFeature. GATE: on/off captures differ as intended; no back-buffer error.
6. Variants. VariantJobs.StrippingSettings (strict matching on), BuildShaderBundle for the shipping materials, parse_variant_funnel, variant_budget_check, strip rules or KeywordOverrides (Shader Build Settings), PostProcessingAudit (every VolumeProfile under Assets/ keeps its post variants). GATE: shipped count per shader under budget; logger total equals Unity's "After scriptable stripping"; overrides cleared or committed on purpose.
7. First-use stutter. PsoJobs.BuildPsoScene, ut_run.build(development=True), ut_shaders.run_pso_player trace, cold, warm; PsoJobs.InspectCollection; ship StreamingAssets/PSO/<platform>_<api>.graphicsstate read by AgentPsoProbe. GATE: pso_gate clean (cold shows uploads, warm shows none by marker and by log).
8. Cost. GpuCostJobs.MeasureFullscreenCost A/B, interleaved, async compilation off (precision_model for half tests). GATE: faster in ms beyond noise; device numbers from a development player (scenario-unity-performance).
9. Deliver. Shaders, materials, feature assets, .graphicsstate per API, and the evidence packet (Handoffs).

Numbers