Why doesn't vsg::Builder have a createMesh(vertexarray, indexarray) method?

[dov]

I'm curious why the vsg::Builder() does not have a createMesh() method that creates a mesh from a list of vertices and faces? Is it simply that nobody has had any need for it, or is there some deeper reason? If the answer is the former, I might try to create a PR to add such a function.

Thanks!

[robertosfield]

vsg::Builder was created to generate primitive shapes, it's been my intention to eventually expand support to include meshes, but there are many other tasks on my TODO list so it's not been something I've tackled.

You are welcome to add an implementation for meshes, it's potentially quite an open ended tasks so getting the API right might be something that takes a few tries.

[dov]

I tried adding a Builder::createMesh() method based on the other create... methods in the builder, and all I really did was to change the creation vertices, normals, and faces, so that they are received externally. Here is my method:

ref_ptr<Node> Builder::createMesh(ref_ptr<vec3Array> vertices, ref_ptr<vec3Array> normals, ref_ptr<ushortArray> indices, const GeometryInfo& info, const StateInfo& stateInfo)
{
    // currently assume no subgraph

    uint32_t instanceCount = 1;
    auto positions = instancePositions(info, instanceCount);
    auto colors = instanceColors(info, instanceCount);

    if (info.transform != identity)
    {
        transform(info.transform, vertices, normals);
    }

    // setup geometry
    auto vid = VertexIndexDraw::create();

    DataList arrays;
    arrays.push_back(vertices);
    if (normals) arrays.push_back(normals);
    if (colors) arrays.push_back(colors);
    if (positions) arrays.push_back(positions);
    vid->assignArrays(arrays);

    vid->assignIndices(indices);
    vid->indexCount = static_cast<uint32_t>(indices->size());
    vid->instanceCount = instanceCount;

    return decorateAndCompileIfRequired(info, stateInfo, vid);
}

I then created a small test based on vsgExample vsgBuilder.cpp and created my main node as follows:

int main(int argc, char **argv)
{
    auto windowTraits = vsg::WindowTraits::create();
    windowTraits->windowTitle = "hello-mesh-builder";

    auto builder = vsg::Builder::create();
  
    auto scene = vsg::Group::create();

    vsg::GeometryInfo geomInfo;
    vsg::StateInfo stateInfo;

    // Change box color to red
    geomInfo.color = vsg::vec4 {1.0f, 0.0f, 0.0f, 1.0f};

    // Create a mesh by primitives
    auto vertices = vsg::vec3Array::create(
        {{-0.5f, -0.5f, 0.0f},
         {0.5f, -0.5f, 0.0f},
         {0.5f, 0.5f, 0.0f},
        }); 
    auto indices = vsg::ushortArray::create({0, 1, 2}); 
    auto normals = vsg::vec3Array::create(
        {{0.0f, 0.0f, 1.0f},
         {0.0f, 0.0f, 1.0f},
         {0.0f, 0.0f, 1.0f}}); 

    auto node = builder->createMesh(vertices, normals, indices, geomInfo, stateInfo);

    scene->addChild(node);

    // compute the bounds of the scene graph to help position the camera
    vsg::ComputeBounds computeBounds;
    scene->accept(computeBounds);
    vsg::dvec3 centre = (computeBounds.bounds.min + computeBounds.bounds.max) * 0.5;
:

However, when running the result I get a black window, and my whole the system becomes unresponsive. Any idea of what I did wrong? Should I create a minimum reproducible example?