Vertex for the shader-driven animated-quad pipeline (procedural
and sprite kinds). All four vertices of a quad carry the same
slot, which the fragment shader uses to look up per-frame state
(phase, resolved colors, atlas dims) in the anim_uniforms buffer.
No color or timing is baked in the vertex — that’s the whole point:
rebuilding the vertex batch is unnecessary when only the phase
changes, so the widget’s paint() doesn’t re-run per frame.
Vertex for the gradient-filled path pipeline (Tier 3 arbitrary paths
filled with a Paint gradient — linear/radial/conic). Solid-filled
paths keep using the lean QuadVertex/quad_pipeline, tinted by a
flat vertex color (see path_quad_verts in renderer.rs); this
vertex type is only built when PathEntry::paint_data is a gradient
variant, and is drawn by the dedicated path_gradient pipeline
(shaders/path_gradient.wgsl).