First step to add support for 3D scanned walls

[smudrak]

A library (or a set of libraries) is needed in therion, that will be able to:

• load 3D scanned mesh in glTF format including textures
• transform geometry of this 3D mesh (just change coordinates of every vertex)
• join multiple meshes together and write them in a single glTF file including textures

[Afforix]

Existing libraries:

• VTK
  • ➕ is therion dependency
  • ➕ can directly render glTF scene
  • ➖ glTF support from version 9 (Ubuntu 22.04+)
• tinygltf
  • ➕ direct access to the glTF structure
  • ➕ minimal dependencies
• libgltf
  • ➖ more dependencies

[Afforix]

If we choose to use OBJ, library rapidobj looks promising, it has simple interface, uses standard C++ types, and is very fast: https://aras-p.info/blog/2022/05/14/comparing-obj-parse-libraries/.

Simple example:

#include "rapidobj.hpp"

#include <iostream>

int main(int argc, char** argv)
{
    if (argc != 2)
    {
        std::cerr << "Input file path expected\n";
        return 1;
    }

    // Load the model
    auto result = rapidobj::ParseFile(argv[1]);
    if (result.error)
    {
        std::cerr << "Failed to load model: " << result.error.code.message() << "\n";
        return 1;
    }

    const auto& mesh = result.attributes.positions;

    // Iterate through the positions and print them
    // Note: Positions are stored as a flat array of floats,
    // with every 3 values representing the x, y, z components of a vertex position.
    for (size_t i = 0; i < mesh.size(); i += 3)
    {
        std::cout << "Vertex " << (i / 3) << ": "
                  << mesh[i] << ", "
                  << mesh[i + 1] << ", "
                  << mesh[i + 2] << "\n";
    }

    return 0;
}

[Afforix]

Or we can try to stick with VTK:

#include <vtkSmartPointer.h>
#include <vtkOBJReader.h>
#include <vtkPolyData.h>
#include <vtkPoints.h>

int main(int argc, char *argv[])
{
    if(argc != 2)
    {
        std::cerr << "Usage: " << argv[0] << " Filename(.obj)" << std::endl;
        return 1;
    }

    // Create a VTK reader for OBJ files
    vtkSmartPointer<vtkOBJReader> reader = vtkSmartPointer<vtkOBJReader>::New();
    reader->SetFileName(argv[1]);
    reader->Update(); // Load the .OBJ file

    // Get the loaded geometry
    vtkPolyData* polyData = reader->GetOutput();

    // Access the vertices
    vtkPoints* points = polyData->GetPoints();

    // Iterate over and print each vertex
    for(vtkIdType i = 0; i < points->GetNumberOfPoints(); i++)
    {
        double p[3];
        points->GetPoint(i, p);
        // p contains the x, y, z coordinates of the vertex
        std::cout << "Vertex " << i << ": (" << p[0] << ", " << p[1] << ", " << p[2] << ")" << std::endl;
    }

    return 0;
}