javascript - BufferGeometry offsets and indices -

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i wondering while "offsets" , "indices / index" are. offsets e.g. mentioned in https://github.com/mrdoob/three.js/blob/dev/src/core/buffergeometry.js , indices mentioned in indexedgeometry, can't find anymore in dev tree. although indices seem rather obvious , although dive code figure out maybe-correct answer myself i'd love hear "official" statement :)

thanks!

there 2 ways 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 mode every triangle position defined , 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 mode, indices define order of data. first triangle using indices 0, 1, , 2. these indices used fetch vertices , normals data:

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

the main benefit of indexed possibility of reusing data , uploading less data 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 can render specific ranges of geometry. instead of drawing triangle 0 triangle.length, can draw triangle 200 triangle 400.


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