Add a Parallax Mapping manual page

[mvaligursky]

Warning

Do not merge until Engine v2.22 is released. parallaxMode, parallaxSamples, parallaxShadowSamples and heightMapBase do not exist in v2.21 (heightMapBase also needs playcanvas/engine#9245 merged), and the two EngineExample embeds point at examples (materials/parallax-mapping, materials/parallax-terrain) whose thumbnails are only served once the 2.22 examples site deploys.

Description

Parallax mapping had no page of its own. The only coverage was one sentence in the model authoring guide about normal-map alpha, and a four row table in the material inspector reference — neither of which mentions that there are now two modes, that the zero level of the relief is configurable, or that the relief can shadow itself.

New page: user-manual/graphics/physical-rendering/parallax-mapping, added to that category between Physical Materials and Image Based Lighting.

• The two modes — PARALLAX_OFFSET (default, single tap) and PARALLAX_OCCLUSION (ray marched), from Add parallax occlusion mapping as an opt-in parallax mode engine#9213.
• The zero level — heightMapBase, from Add heightMapBase to unify the parallax zero level across modes engine#9245. Both modes read the map the same way: the base value sits at the geometry, relief above it stands out and relief below it sinks in, with 0.5 the mid-grey pivot default and 1 the depth-only reading for white-floor/dark-crack maps.
• Sample budget — parallaxSamples is a cap, not a fixed count, and the march scales down with view angle and distance until the effect fades out entirely, so distant surfaces cost nothing.
• Self shadowing — parallaxShadowSamples, from Add soft self shadowing of the height field to parallax occlusion mapping engine#9225. Directional lights only, zero disables it, and it only appears where the light rakes across the grain of the height map — including the counter-intuitive part, that lowering the light does not give more of it.
• Limitations — no silhouette change, the depth buffer sees the flat surface (so shadows, SSAO and the pre-pass do not follow the relief), and the texture slides at grazing angles.

Correction: the material inspector page said parallax "Requires a normal map to be set". That stopped being true in playcanvas/engine#9207; the sentence now points at the new page instead.

The Japanese translation is included for both files.

Notes

• The inspector page's property table still lists only Heightmap / UV Channel / Color Channel / Strength, because the Editor does not expose the mode, the base or the sample counts yet — Expose the standard material parallax mode in the material inspector editor#2216 tracks that. Worth a follow-up pass once it lands.
• Verified with a full npm run build: both locales build with no broken links, and the new page appears in the sidebar and renders both example embeds.

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