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blender_baking_guide.md

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Blender lightmap to GLTF baking guide

Baking lighting to textures

There may be an easier way but this is how I've done it.

  1. Merge all your objects to a single object (select all and Join)
  2. Create a 1024x1024 empty image. Let's call it Lightmap.
  3. Create a UV map with Smart UV Project (press U in edit mode)
    • Margin: 0.05 worked OK for me.
  4. For all materials you wish to bake, add an unused Image Texture node and choose Lightmap from the menu:
  5. From the Render Properties tab, find the Bake button.
    • If it's super slow, lower Max Samples to 32 for example under the Sampling section.

Make sure your model has enough vertices to represent the baked lighting by subdividing it a few times in edit mode:

GLTF export

  1. For export, add your new Lightmap texture as the Base Color for one material. Do it by clicking that yellow dot on the left of the RGB picker.
  2. Assign that material to all faces you are going to export. This makes them a single "GLTF primitive".
  3. Export a GLTF.

GLTF export settings

Format: glTF Separate (.gltf + .bin + textures). Disable Normals and Vertex Colors export.

Normals cause discontinuities and vertex colors are written by the baker so they are not welcome in the input mesh.

How to enable backface culling

The GLTF exporter uses a per-material setting to decide if surfaces or one or two-sided. You usually want all to be one-sided so please enable backface culling for exported materials.

In Cycles materials under Viewport Info:

In Eevee materials under Settings:

Viewport backface culling

To check if your triangles are pointing the right direction, enable viewport backface culling under the Viewport Shading menu: