I was just wondering for a while now what exactly "offsets" and "indices / index" are. Offsets are e.g. mentioned in .js/blob/dev/src/core/BufferGeometry.js and indices were mentioned in IndexedGeometry, however I can't currently find it anymore in the dev tree. Although indices seem rather obvious and although I could dive into the code to figure out some maybe-correct answer for myself I'd love to hear an "official" statement :)

Thanks!

I was just wondering for a while now what exactly "offsets" and "indices / index" are. Offsets are e.g. mentioned in https://github./mrdoob/three.js/blob/dev/src/core/BufferGeometry.js and indices were mentioned in IndexedGeometry, however I can't currently find it anymore in the dev tree. Although indices seem rather obvious and although I could dive into the code to figure out some maybe-correct answer for myself I'd love to hear an "official" statement :)

Thanks!

• javascript
• three.js
• indices
• buffer-geometry

Share Improve this question Follow edited Feb 3, 2016 at 16:04 Wilt 44.6k1515 gold badges161161 silver badges214214 bronze badges asked May 30, 2014 at 6:47 DoidelDoidel 1,77911 gold badge1616 silver badges2121 bronze badges

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Sorted by: Reset to default 8

There are two ways to defining geometries:

Non-Indexed

"vertices": [ 0, 1, 2,  3, 4, 5,  6, 7, 8,  ... ],
"normals":  [ 0, 1, 2,  3, 4, 5,  6, 7, 8,  ... ]

In this mode every triangle position is as defined and you can't reuse data.

triangle 0: [ 0, 1, 2,  3, 4, 5,  6, 7, 8 ]

Indexed

"indices":  [ 0, 1, 2, ... ],
"vertices": [ 0, 1, 2,  3, 4, 5,  6, 7, 8,  ... ],
"normals":  [ 0, 1, 2,  3, 4, 5,  6, 7, 8,  ... ]

In this mode, indices define the order of the data. The first triangle is using indices 0, 1, and 2. These indices will be used to fetch the vertices and normals data:

triangle 0: [ 0, 1, 2,  3, 4, 5,  6, 7, 8 ]

The main benefit of indexed is the possibility of reusing data and uploading less data to the GPU:

"indices":  [ 0, 0, 0, ... ],
"vertices": [ 0, 1, 2,  3, 4, 5,  6, 7, 8,  ... ]

triangle 0: [ 0, 1, 2,  0, 1, 2,  0, 1, 2 ]

As per offsets...

With offsets you can render specific ranges of your geometry. Instead of drawing from triangle 0 to triangle.length, you can draw from triangle 200 to triangle 400.