NAME

htrdr-obj — geometric file format

DESCRIPTION

A htrdr-obj file is an ordinary obj file composed solely of triangular meshes. Its special feature is that each triangle must be included in a material group as defined by the usemtl directive. And the form of the usemtl directive must be as follows:

with front-mtl, interface-mtl and back-mtl the material names of the front, interface and back of the triangles belonging to the group. The interface material name is optional: it is used for thin geometries, i.e. geometries with no thickness. Material names can be composed of any character, with the exception of spaces, tabs and the colon character used to separate the aforementioned names. Note that, by convention, a side of a triangle is said to be "front-facing" when its vertices are ordered clockwise.

The grammar of a htrdr-obj file is therefore a subset of the obj file format, with only one specific convention concerning material names. Consequently, any software supporting the obj file format can be used to create or view a htrdr-obj file.

EXAMPLES

Define a sheet of paper at the interface between air and concrete:

v -1.0  -1.0  0
v -1.0   1.0  0
v  1.0  -1.0  0
v  1.0   1.0  0

usemtl air:paper:concrete
f 1 2 3
f 3 2 4

Define a wooden cube whose faces along the Z axis are against a brick. The other faces are in contact with the air:

v 0 0 0
v 1 0 0
v 0 1 0
v 1 1 0
v 0 0 1
v 1 0 1
v 0 1 1
v 1 1 1

usemtl wood:air
f 1 3 2
f 2 3 4
f 1 5 3
f 3 5 7
f 5 6 7
f 7 6 8
f 4 8 2
f 2 8 6

usemtl wood:brick
f 3 7 4
f 4 7 8
f 1 2 5
f 5 2 6

HISTORY

The htrdr-obj format was first developed for the htrdr(1) program.