Draw keywords

A player stores one compiled program per keyword set (shader objects). Which set a draw uses is the renderer’s choice each frame, from the frame’s lights, shadows, fog and probes; nothing public states it exactly. The rules below were measured by rendering a probe shader that was compiled with the same multi_compile lines as the engine’s own shaders and that writes one bit per keyword it was compiled with into the pixel it draws; the pixel is read back from a render texture. The editor was Unity 6000.6.4f1 with the Universal Render Pipeline package 17.6.0 (Direct3D 12, with graphics enabled: the shaders have to run). Observed

The games were built with other versions (2019.4.20f1 for SkateBIRD, 6000.3.12f1 for Sledding Game), so the rules are the newer editor’s. Two cross-checks that they hold for the players: every stored variant of a pass carries the keywords the rules predict, and the settings read from each quality level’s URP asset (script fields) agree with which keywords the build stripped. Observed · Sledding

Built-in pipeline, forward base pass

The pass compiles with multi_compile_fwdbase, multi_compile_fog and multi_compile_instancing. Observed

Keyword	Set when	Confidence
DIRECTIONAL	on every draw, whatever the lights (no light, intensity 0)	Observed
LIGHTPROBE_SH	on every draw that is not lightmapped; light probe usage Off and the ambient mode do not change it	Observed
SHADOWS_SCREEN	exactly when the sun casts shadows (hard or soft), the quality level draws shadows, and the renderer receives them	Observed
FOG_LINEAR, FOG_EXP, FOG_EXP2	fog is on, by its mode	Observed
INSTANCING_ON	the material enables instancing and two draws share it	Observed
VERTEXLIGHT_ON	not set by one or two point lights (the quality level’s pixel light count of 4 makes them pixel lights); needs a light forced per vertex or more lights than the pixel light count; not observed set	Observed

Lightmap keywords were not tested. Observed

SkateBIRD’s stored variants all carry DIRECTIONAL (so a pass resolves it as implied). SHADOWS_SCREEN is on 192 of the 198 draws of its first level; the other 6 are renderers that do not receive shadows. Observed · SkateBIRD

Universal Render Pipeline, forward path

Keyword	Set when	Confidence
_MAIN_LIGHT_SHADOWS	the asset supports shadows and lights the main light per pixel, with 1 cascade; and also for a sun without shadows or a shadow distance of 0 (the pipeline binds an empty shadow map and sets it)	Observed
_MAIN_LIGHT_SHADOWS_CASCADE	the main light casts shadows within the shadow distance and the asset has 2 or 4 cascades	Observed
neither	shadows unsupported in the asset, or the main light per vertex	Observed
_SHADOWS_SOFT	the asset supports soft shadows and the sun’s shadows are soft	Observed
_ADDITIONAL_LIGHTS / _ADDITIONAL_LIGHTS_VERTEX	by the asset’s additional lights mode (per pixel, per vertex), whether or not an additional light exists; none when disabled	Observed
_CLUSTER_LIGHT_LOOP	the Forward+ rendering path	Observed
_ADDITIONAL_LIGHT_SHADOWS	the asset supports them and a shadow-casting additional light exists	Observed
_LIGHT_LAYERS	the asset supports light layers	Observed
_LIGHT_COOKIES	never set by the asset’s setting alone in the cases tried; no case had a light with a cookie	Observed
_REFLECTION_PROBE_BLENDING, _REFLECTION_PROBE_BOX_PROJECTION	the asset’s two settings	Observed
_REFLECTION_PROBE_ATLAS	Forward+ with blending	Observed
fog keywords	as the built-in pipeline’s	Observed

_MIXED_LIGHTING_SUBTRACTIVE was never set in the cases tried; the deferred path draws no forward pass. Observed

Keywords the frame’s lights or an object’s position decide (VERTEXLIGHT_ON, the lightmap and shadowmask keywords) and keywords that depend on the renderer’s features (_SCREEN_SPACE_OCCLUSION, _DBUFFER_MRT3, _ADDITIONAL_LIGHT_SHADOWS) are not derived from the scene alone: where every stored variant of a stage has a keyword, the keyword is taken as implied. Inferred

Effect of getting the keyword set wrong

Sledding Game’s mountain scene: of 164 materials on URP shaders (last quality level), 20 find a stored variant with no keywords or the commonest set, and all 164 find one with the scene’s keywords. The 144 that find none without them all lack a keyword of one group, _MAIN_LIGHT_SHADOWS or _MAIN_LIGHT_SHADOWS_CASCADE, which the URP asset’s cascade count decides. Inferred · Sledding SkateBIRD’s first level: 2 of 198 materials find a variant with none, all 198 with the build-implied DIRECTIONAL, and 198 with the scene’s keywords. Inferred · SkateBIRD