DecalOptions

interface DecalOptions

import type { DecalOptions } from '@driftengine/core';

In depth

A forward renderer cannot write a decal cheaply into a G-buffer, because there is no G-buffer, and that is the fact every decal design here has to start from. What a forward renderer can do is the older technique, and it is the better-looking one: take the triangles the projector box covers, clip them to it, and draw that. The decal is then made of the surface, so it follows every curve and every bump exactly, which a projector re-drawing a quad cannot.

What it replaces, in a consumer's own words. Their road patches are strips of geometry lifted two millimetres above the carriageway: it works, it is a draw call per patch for something that exists only to sit on top of something else, and it does not follow a curved surface. Puddles after a storm, oil stains and skid marks were all waiting on the same row. This is one mesh for as many marks as you project into it, and it is the road's own shape.

Built once, not per frame. A decal is authored or placed by an event — a tyre locks, a barrel leaks — and then it is scenery. That is what makes clipping on the CPU the right cost: it happens at the moment the mark is made, and every frame afterwards it is one more mesh in the batch.

Its limits, stated rather than discovered. It is a static decal: the receiving mesh is sampled as it is, so a decal on something that later deforms rides the old shape. It reads positions and normals and nothing else, so the mark takes its own colour rather than tinting what is underneath. And a projector box covering a hundred thousand triangles clips a hundred thousand triangles, so a caller marking a large world hands in the piece of it they mean.

Properties