@li-plus Awesome!

Its obj file defines the same mtllib 181 times, and tinyobjloader will reload the file the same number of times! This mtllib file has 42 newmtl statements, so finally reader.GetMaterials() returns 7602 materials

I see. Let us give some time to figure out the solution. It may require adding extra data structure and may break current API design to support multiple newmtl statements

Thanks for your attention! Just to be clear, multiple newmtl has no problem. What really matters is multiple mtllib statements. The obj file of "Living Room" scene is like:

mtllib living_room.mtl
usemtl MiddleLight
g Default
f 1/1/1 2/2/2 3/3/3 4/4/4
usemtl LeftLight
f 8/2/5 7/1/6 6/5/7 5/6/8
usemtl RightLight
f 11/7/9 12/8/10 10/4/11 9/3/11
......
mtllib living_room.mtl
usemtl Books
g Default
f 2106/2263/1506 2108/2264/1506 2107/2265/1506
......
mtllib living_room.mtl
usemtl DullSteel
g Default
f 2154/2291/1516 2156/2292/1516 2155/2293/1516
......

I have finally worked out a solution: memorize all the material_maps in an std::map indexed by mtllib filenames. Every time before I need to load an mtllib, I will check if it is already loaded. If already loaded, the material_map stored in memory will be returned. It works perfectly for me. You may review and merge this PR, or you might have your own implementation though.

I just figured out a simpler way. When multiple mtllib statements are defined, only load the first one, and send warnings on the rest.

@li-plus

When multiple mtllib statements are defined, only load the first one, and send warnings on the rest.

Awesome! Let us give some time to review the PR

@li-plus After reading the .obj spec

https://en.wikipedia.org/wiki/Wavefront_.obj_file
http://paulbourke.net/dataformats/obj/

The spec says

mtllib filename1 filename2 . . .

    Polygonal and free-form geometry statement.

    Specifies the material library file for the material definitions
    set with the usemtl statement. You can specify multiple filenames
    with mtllib. If multiple filenames are specified, the first file
    listed is searched first for the material definition, the second
    file is searched next, and so on.

    When you assign a material library using the Model program, only
    one map library per .obj file is allowed. You can assign multiple
    libraries using a text editor.

one map library is a typo(this should be corrected as one material library). the Model program refers the modeling program(i.e., Wavefront 3D program)

So the spec itself allows multiple definition of mtllib in .obj. Thus,

If already loaded, the material_map stored in memory will be returned

You need to revert PR to the version of this: Cache mtllib command.

@syoyo You are correct. I reverted this PR to cache mtllib filenames, which supports multiple mtllib files in multiple statements. The behavior does not change except for no reloading the same file.

@li-plus Thanks! Merged!