There are some slight changes in the size of the glTF JSON itself.
The reason the data doesn’t shrink down all the way to 50% is because a portion of the binary data buffer is made up of indices that cannot be quantized.Īpplying gzip to models shrinks the gap between the quantized and non-quantized file sizes, but ultimately the quantized models still have a size advantage over their non-quantized counterparts and use less GPU memory. StatisticsĪs expected, the model with more geometry benefits more from this compression, but even the model whose file size is mostly impacted by texture benefits from what is effectively free compression. 2 Cylinder EngineĪ geometry-heavy model donated to the glTF sample models repository by Okino Polytrans Software. To illustrate this, I’ve included a synopsis using two models in the glTF sample models repository. So files that have complex geometry tend to benefit the most. Quantization works best on models whose file size is composed mostly of quantizable attributes, such as positions and normals. The decompression is done by a simple matrix multiplication in parallel in the vertex shader on the GPU. This means that the attribute data can be stored in half the amount of space! Quantization takes those attributes and stores them as 16-bit integers represented on a scale between the minimum and maximum values. Usually model attributes such as positions and normals are stored as 32-bit floating-point numbers. The WEB3D_quantized_attributes extension is based on Mesh Geometry Compression for Mobile Graphics, by Jongseok Lee, et al. Quantized 3D model files means smaller files, faster downloads, and less GPU memory usage with no performance degradation. This meets the needs of 3D Tiles in Cesium perfectly because the 3D Tiles engine frequently downloads new tiles based on the view. The WEB3D_quantized_attributes extension to glTF offers reasonable compression with little to no overhead for decompression.
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