L20 — Vertex paint & color layers

Goal

Paint per-vertex colors for terrain tints. Name layers the pipeline expects (Col, optional Alpha).

Why (again)

Module 1–2: multiply texture × vertex color for cheap dirt paths and biome shifts. Now you author that paint.

Steps

1. Select mesh → Vertex Paint mode (mode menu).
2. Ensure a color attribute exists named Col (Data / Color Attributes panel).
3. Brush soft falloff; paint grass vs path.
4. For Fast64, you may also need Alpha.

Make glTF export keep colors

Vanilla Blender only exports vertex colors if the material uses them (or certain export flags). Course generator hooks Col → Principled Base Color so COLOR_0 is written.

If your export lacks colors:

• Connect Attribute / Color Attribute node to Base Color, or
• Use Fast64 materials (L21), which are designed for this pipeline

Island exercise

Paint a darker strip across a ground plane as a path. Rebuild via inject + gltf_to_t3d or Fast64 export. View in Asset lab.

Lesson code

Module 3 is Blender-first — there is no per-lesson C ROM for L17–L25.

Runnable code that loads the course meshes lives in the Module 3 asset lab checkpoint (lessons/m3-asset-lab/).

Next

L21 — Fast64 & export.