The example code for the new OO API isn't quite right

[erich666]

Describe the issue
For this main readme file: https://github.com/tinyobjloader/tinyobjloader/blob/master/README.md#example-code-new-object-oriented-api

This "Example code (New Object Oriented API)" code works well to read in cornell_box.obj. There's just one minor issue flagged by Visual Studio, that "v" and "fv" are of different types (size_t vs. int).

But, the access code:

            tinyobj::index_t idx = shapes[s].mesh.indices[index_offset + v];
            tinyobj::real_t vx = attrib.vertices[3 * idx.vertex_index + 0];
            tinyobj::real_t vy = attrib.vertices[3 * idx.vertex_index + 1];
            tinyobj::real_t vz = attrib.vertices[3 * idx.vertex_index + 2];
            tinyobj::real_t nx = attrib.normals[3 * idx.normal_index + 0];
            tinyobj::real_t ny = attrib.normals[3 * idx.normal_index + 1];
            tinyobj::real_t nz = attrib.normals[3 * idx.normal_index + 2];

fails and asserts when it tries to read the normals, because there are no normals computed.

To Reproduce
Steps to reproduce the behavior:

1. Compile in some new, basic console app the example code https://github.com/tinyobjloader/tinyobjloader/blob/master/README.md#example-code-new-object-oriented-api
2. Run
3. See assert

Expected behavior
A clear and concise description of what you expected to happen.

Here's the fixed code I suggest for the example:

        for (size_t v = 0; v < (size_t)fv; v++) {
            // access to vertex
            tinyobj::index_t idx = shapes[s].mesh.indices[index_offset + v];
            tinyobj::real_t vx = attrib.vertices[3 * idx.vertex_index + 0];
            tinyobj::real_t vy = attrib.vertices[3 * idx.vertex_index + 1];
            tinyobj::real_t vz = attrib.vertices[3 * idx.vertex_index + 2];
            if (idx.normal_index >= 0) {
                tinyobj::real_t nx = attrib.normals[3 * idx.normal_index + 0];
                tinyobj::real_t ny = attrib.normals[3 * idx.normal_index + 1];
                tinyobj::real_t nz = attrib.normals[3 * idx.normal_index + 2];
            }
            if (idx.texcoord_index >= 0) {
                tinyobj::real_t tx = attrib.texcoords[2 * idx.texcoord_index + 0];
                tinyobj::real_t ty = attrib.texcoords[2 * idx.texcoord_index + 1];
            }
            // Optional: vertex colors
            // tinyobj::real_t red = attrib.colors[3*idx.vertex_index+0];
            // tinyobj::real_t green = attrib.colors[3*idx.vertex_index+1];
            // tinyobj::real_t blue = attrib.colors[3*idx.vertex_index+2];
        }

Environment

• TinyObjLoader version v2-rc1
• OS: Windows 10
• Compiler Visual Studio
• Other environment - none

[syoyo]

@erich666 Good issue!

I have created PR to fix/update example code in README.md. Could you please check it? #301

[erich666]

I gave it a compile and run, the added code worked fine. Is there a way to test if there are RGB colors per vertex? I never use that format, so don't know about it.

            // Optional: vertex colors
            // tinyobj::real_t red = attrib.colors[3*idx.vertex_index+0];
            // tinyobj::real_t green = attrib.colors[3*idx.vertex_index+1];
            // tinyobj::real_t blue = attrib.colors[3*idx.vertex_index+2];

Anyway, other than that bonus test, if there is one, looks good.

[syoyo]

@erich666 thanks! > I gave it a compile and run, the added code worked fine

There is an example to display vertex color of .obj data in NanoRT example:

https://github.com/lighttransport/nanort/tree/master/examples/gui