[x3d-public] remove SF/MFInt32 ?

John Carlson yottzumm at gmail.com
Tue Apr 10 00:21:10 PDT 2018

I wonder if there's any compression/decompression going to the graphics
card?   Or is it not worth compressing?



On Tue, Apr 10, 2018, 12:15 AM Michalis Kamburelis <michalis.kambi at gmail.com>

> 2018-04-10 4:40 GMT+02:00 Andreas Plesch <andreasplesch at gmail.com>:
> > Another way to approach the question if there is an opportunity or if
> such
> > an idea is just a distraction, is to consider why there is not a SFInt16
> or
> > SFInt8 type. The thinking at the time may have been that there is a need
> for
> > integers for indices but also a need to keep it simple and only have a
> > single one, int32. On the other hand, for floats let's have both 32 and
> > 64bit.
> Note that it is a reasonable optimization to pack mesh indexes into
> 8-bit or 16-bit integers, instead of full 32-bit integers. Even today,
> with incredibly fast GPUs :)
> Looking at others:
> - glTF 2.0 allows providing indexes as 8-bit or 16-bit integers
> (https://github.com/KhronosGroup/glTF/tree/master/specification/2.0
> allows to use UNSIGNED_SHORT, UNSIGNED_BYTE as an alternative to
> UNSIGNED_INT for indexes).
> - And the APIs -- like OpenGL[ES], WebGL, Three.js -- all allow
> indexes to be 8-bit or 16-bit integers, not only 32-bit integers.
> - Unity3d explicitly advices using 16-bit indexes for meshes, not 32:
> https://docs.unity3d.com/Manual/FBXImporter-Model.html : "Note: For
> bandwidth and memory storage size reasons, you generally want to keep
> 16 bit indices as default, and only use 32 bit when necessary." . Note
> that it's a new setting -- before 2017, Unity3d was *forcing* to use
> 16-bit indices, limiting all mesh sizes to 64k chunks, and there
> wasn't even an option to use 32-bit indices.
> - In Castle Game Engine, we use 16-bit indexes for rendering on
> OpenGLES (mobile) and for all 2D user-interface rendering. We keep
> using 32-bit indexes on desktop OpenGL for 3D rendering.
> I'm not proposing to introduce MFInt16 to X3D :) But I wanted to note
> that "the size of integers still matters for GPUs". While the hardware
> is incredibly faster than it was 20 years ago, some of the "old"
> optimizations still matter. The gain you get from using smaller types
> still matters when you have a large mesh data and need to send it fast
> to GPU. ("coordIndex" expressed using 16-bit ints is 2x smaller than
> 32-bit ints, "Coordinate.point" expressed using half-floats is 2x
> smaller than 32-bit floats and so on.)
> Regards,
> Michalis
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