Creates a vertex array to draw a sphere in OpenGL

sphere.cpp

#include <vector>
#include <cmath>

struct vec3 {
    float x, y, z;
    void set(float X, float Y, float Z)
    {
        x = X;
        y = Y;
        z = Z;
    }
};

vec3 midpoint(vec3 a, vec3 b)
{
    vec3 c;
    c.x = .5f * (a.x + b.x);
    c.y = .5f * (a.y + b.y);
    c.z = .5f * (a.z + b.z);
    return c;
}

std::vector<float> drawTriangle(vec3 v1, vec3 v2, vec3 v3)
{
    std::vector<float> triangles;
    triangles.push_back(v1.x);
    triangles.push_back(v1.y);
    triangles.push_back(v1.z);
    triangles.push_back(v2.x);
    triangles.push_back(v2.y);
    triangles.push_back(v2.z);
    triangles.push_back(v3.x);
    triangles.push_back(v3.y);
    triangles.push_back(v3.z);
    return triangles;
}

void subdiv(vec3 v1, vec3 v2, vec3 v3, std::vector<float> & sphereQuadrant, int level)
{
    if (level == 0)
        //appends the triangle to the sphere quadrant vector:
        sphereQuadrant.insert(sphereQuadrant.end(), drawTriangle(v1, v2, v3).begin(), drawTriangle(v1, v2, v3).end());
    else {
        vec3 v12, v13, v23;
        v12 = midpoint(v1, v2);
        v13 = midpoint(v1, v3);
        v23 = midpoint(v2, v3);
        float r = 1.0f / std::sqrt(v12.x * v12.x + v12.y +v12.y + v12.z + v12.z);
        v12.x *= r;
        v12.y *= r;
        v12.z *= r;
        r = 1.0f / std::sqrt(v13.x * v13.x + v13.y * v13.y + v13.z * v13.z);
        v13.x *= r;
        v13.y *= r;
        v13.z *= r;
        r = 1.0f / std::sqrt(v23.x * v23.x + v23.y * v23.y + v23.z * v23.z);
        v23.x *= r;
        v23.y *= r;
        v23.z *= r;
        subdiv(v1,  v12, v13, sphereQuadrant, level - 1);
        subdiv(v12, v2,  v23, sphereQuadrant, level - 1);
        subdiv(v13, v23, v3,  sphereQuadrant, level - 1);
        subdiv(v12, v23, v13, sphereQuadrant, level - 1);
    }
}

//this is the function you call.  Create a vector of vertices send that in sphere.  Prec controls how many triangles:

void createSphere(std::vector<float> & sphere, int prec)
{
    vec3 v1, v2, v3;
    v1.set(0.0f, 1.0f, 0.0f);
    v2.set(1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, 1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, 1.0f, 0.0f);
    v2.set(-1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, 1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, 1.0f, 0.0f);
    v2.set(1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, -1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, 1.0f, 0.0f);
    v2.set(-1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, -1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, -1.0f, 0.0f);
    v2.set(1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, 1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, -1.0f, 0.0f);
    v2.set(-1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, 1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, -1.0f, 0.0f);
    v2.set(1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, -1.0f);
    subdiv(v1, v2, v3, sphere, prec);
    
    v1.set(0.0f, -1.0f, 0.0f);
    v2.set(-1.0f, 0.0f, 0.0f);
    v3.set(0.0f, 0.0f, -1.0f);
    subdiv(v1, v2, v3, sphere, prec);
}