Create example of how to create a gltf file from scratch

[dov]

I'm creating my own mesh and I would like to save the result into a gltf file. There are no examples or documentation about how to do this.

[prideout]

Yes this would be useful since the test we have currently doesn't create one from scratch.

One strategy is to declare a lot of things on the stack, e.g.:

    cgltf_image images[3] = {
        {(char*)"tile color", (char*)"tile_color.png"},
        {(char*)"tile orm", (char*)"tile_orm.png"},
        {(char*)"tile normal", (char*)"tile_normal.png"},
    };
    cgltf_image& color_image = images[0];
    cgltf_image& orm_image = images[1];
    cgltf_image& normal_image = images[2];

    cgltf_texture textures[3] = {
        {(char*)"tile color", &color_image},
        {(char*)"tile orm", &orm_image},
        {(char*)"tile normal", &normal_image},
    };
    cgltf_texture& color_texture = textures[0];
    cgltf_texture& orm_texture = textures[1];
    cgltf_texture& normal_texture = textures[2];

    cgltf_material materials[4] = {};
    cgltf_material& tile_bottom_material = materials[0];
    cgltf_material& tile_top_material = materials[1];
    cgltf_material& tile_glow_material = materials[2];
    cgltf_material& player_material = materials[3];

    tile_top_material.name = (char*)"tile top";
    tile_top_material.alpha_cutoff = 0.5f;
    tile_top_material.has_pbr_metallic_roughness = true;
    tile_top_material.pbr_metallic_roughness = {
        .base_color_texture = {&color_texture, 0, 1.0f},
        .metallic_roughness_texture = {&orm_texture, 0, 1.0f},
        .base_color_factor = {1, 1, 1, 1},
        .metallic_factor = 1,
        .roughness_factor = 1,
    };
    tile_top_material.occlusion_texture = {&orm_texture, 0, 1.0f};
    tile_top_material.normal_texture = {&normal_texture, 0, 1.0f};
    etc...

[prideout]

Here's a more complete example of writing a gltf from scratch: https://github.com/prideout/par/blob/master/test/test_octasphere.cpp

We could add a pointer to this from the README, or we could copy it into a unit test. I'll defer to @jkuhlmann on how best to proceed.