SparrowRenderer/src/parametricmesh.cpp

#include "parametricmesh.h"
#include "glm/ext.hpp"
#include "pbrmaterial.h"

#define M_PI 3.14159265358979323846
#define MAGIC_RATIO 0.37139f

Mesh* MeshGenerator::generateParametricMesh(Material* mat, int width, int height, float size, bool alternate)
{
    m_size = size;
    m_mesh = new Mesh("parametric_mesh");
    m_mesh->setMaterial(mat);
    
    for(int i=0; i<=width; ++i)
    {
        for(int j=0; j<=height; ++j)
        {
            createVertex(float(i)/float(width), float(j)/float(height));
            if(i > 0 && j > 0)
            {
                if(alternate && (i+j)%2)
                {
                    m_mesh->addTriangle(getVertexId(i, j, height),
                                        getVertexId(i, j-1, height),
                                        getVertexId(i-1, j, height));
                    m_mesh->addTriangle(getVertexId(i-1, j-1, height),
                                        getVertexId(i-1, j, height),
                                        getVertexId(i, j-1, height));
                }
                else
                {
                    m_mesh->addTriangle(getVertexId(i, j, height),
                                        getVertexId(i-1, j-1, height),
                                        getVertexId(i-1, j, height));
                    m_mesh->addTriangle(getVertexId(i, j, height),
                                        getVertexId(i, j-1, height),
                                        getVertexId(i-1, j-1, height));
                }
            }
        }
    }
    
    return m_mesh;
}

Mesh* MeshGenerator::generateGeodesicMesh(Material* mat, int n, float size)
{
    m_size = size;
    m_mesh = new Mesh("geodesic_mesh");
    m_mesh->setMaterial(mat);
    
    // icosahedron :

    // top cap
    createVertex(0, 1);
    for(int i=0; i<5; i++)
        createVertex(i/5.f, 1-MAGIC_RATIO);

    // bottom cap
    createVertex(0, 0);
    for(int i=0; i<5; i++)
        createVertex((i+0.5f)/5.f, MAGIC_RATIO);

    // Compute faces
    for(int i=0; i<5; i++){
        int top = 1;
        int bottom = 7;
        int offset = (i+1)%5;
        // top cap
		m_mesh->addTriangle(0, top+offset, top+i);
        // bottom cap
		m_mesh->addTriangle(6, bottom+i, bottom+offset);
        // middle ribbon
		m_mesh->addTriangle(top+i, top+offset, bottom+i);
		m_mesh->addTriangle(top+offset, bottom+offset, bottom+i);
    }

    // geodesic subdivisions :
    for(int i=0; i<n; i++)
        subdivide();
    
    return m_mesh;
}

void MeshGenerator::createVertex(float u, float v)
{
    m_mesh->addVertex(evalUV(u, v)*m_size, glm::vec2(u, v));
}

int MeshGenerator::getEdge(int a, int b)
{
    Edge* current = edges+a;
    int vid = -1;
    while(vid == -1)
    {
        if(current->b == b)
            vid = current->vertex;
        else if(current->next == NULL)
        {
            vid = m_mesh->m_positions3D.size();
			// creating subdivision vertex
			
            // u/v sphériques, cohérents sur toute la sphère sauf des artefacts au niveau des u==0
            glm::vec3 pos = glm::normalize((m_mesh->m_positions3D[a] + m_mesh->m_positions3D[b]) / 2.f);
			float newU = (pos.x < 0 ? 1.5f : 1.f) + atan(pos.z/pos.x)/(2*M_PI);
			float newV = acos(pos.y)/M_PI;
            // alternative, u/v moyennés :
            /*float newU = (m_mesh->texCoords[a].x + m_mesh->texCoords[b].x) / 2.f;
			float newV = (m_mesh->texCoords[a].y + m_mesh->texCoords[b].y) / 2.f;*/
            createVertex(-(newU - floor(newU)), newV);
            
            // inserting the new vertex in the edge collection
            if(current->b == -1)
            {
                current->vertex = vid;
                current->b = b;
            }
            else
                current->next = new Edge(b, vid);
        }
        else
            current = current->next;
    }
    return vid;
}

void MeshGenerator::subdivide()
{
    edges = new Edge[m_mesh->m_positions3D.size()-1];
    int nb_triangles = m_mesh->m_indices.size()/3;
    for(int j=0; j<nb_triangles; j++)
    {
        int vid[3];
        for(int k=0; k<3; k++)
        {
            int idA = m_mesh->m_indices[j*3 + k];
            int idB = m_mesh->m_indices[j*3 + (k+1)%3];
            int a = idA < idB ? idA : idB;
            int b = idA > idB ? idA : idB;
            vid[k] = getEdge(a, b);
        }
        for(int k=0; k<3; k++)
            m_mesh->addTriangle(m_mesh->m_indices[j*3 + k], vid[k], vid[(k+2)%3]);
        m_mesh->addTriangle(vid[0], vid[1], vid[2]);
    }
    delete[](edges);
    m_mesh->m_indices.erase(m_mesh->m_indices.begin(), m_mesh->m_indices.begin()+nb_triangles*3);
}

int MeshGenerator::getVertexId(int i, int j, int height)
{
    return i*(height+1) + j;
}