.DRC

Introduction

Draco is an open source library from Google, released in 2017, for compressing triangle meshes and point clouds. It shrinks vertex positions, normals, colours and texture coordinates by quantising them and predicting each value from its neighbours, which often makes a mesh many times smaller than the same data stored plainly.

A .drc file is a single compressed mesh or point cloud. The same compression is more often met inside glTF files, through the KHR_draco_mesh_compression extension, where a browser decodes it before drawing.

Structure

A Draco file starts with the five bytes DRACO, then the major and minor version of the bitstream, the encoder type (point cloud or triangle mesh), the method (sequential or Edgebreaker, which encodes the mesh connectivity by walking across its triangles) and a 16-bit flags field. Optional metadata follows, then the compressed connectivity and the compressed attributes. The full bitstream is described in a published specification.

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