OpenSpace/src/util/sphere.cpp

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 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2022                                                               *
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#include <openspace/util/sphere.h>

#include <ghoul/logging/logmanager.h>
#include <ghoul/opengl/ghoul_gl.h>
#include <cstring>

namespace {
    constexpr std::string_view _loggerCat = "PowerScaledSphere";
} // namespace

namespace openspace {

Sphere::Sphere(float radius, int segments)
    : Sphere(glm::vec3(radius), segments)
{}

// Alternative Constructor for using accurate triaxial ellipsoid
Sphere::Sphere(glm::vec3 radius, int segments)
    : _isize(6 * segments * segments)
    , _vsize((segments + 1) * (segments + 1))
    , _varray(new Vertex[_vsize])
    , _iarray(new int[_isize])
{
    int nr = 0;
    const float fsegments = static_cast<float>(segments);

    for (int i = 0; i <= segments; i++) {
        // define an extra vertex around the y-axis due to texture mapping
        for (int j = 0; j <= segments; j++) {
            const float fi = static_cast<float>(i);
            const float fj = static_cast<float>(j);
            // inclination angle (north to south)
            const float theta = fi * glm::pi<float>() / fsegments;  // 0 -> PI
            // azimuth angle (east to west)
            const float phi = fj * glm::pi<float>() * 2.f / fsegments;  // 0 -> 2*PI

            // Spherical coordinates based on ISO standard.
            // https://en.wikipedia.org/wiki/Spherical_coordinate_system

            const float x = radius[0] * sin(theta) * cos(phi);
            const float y = radius[1] * sin(theta) * sin(phi);
            const float z = radius[2] * cos(theta); // Z points towards pole (theta = 0)

            _varray[nr].location[0] = x;
            _varray[nr].location[1] = y;
            _varray[nr].location[2] = z;
            _varray[nr].location[3] = 0.0;

            glm::vec3 normal = glm::vec3(x, y, z);
            if (!(x == 0.f && y == 0.f && z == 0.f)) {
                normal = glm::vec3(glm::normalize(glm::dvec3(normal)));
            }

            _varray[nr].normal[0] = normal[0];
            _varray[nr].normal[1] = normal[1];
            _varray[nr].normal[2] = normal[2];

            const float t1 = fj / fsegments;
            const float t2 = 1.f - (fi / fsegments);

            _varray[nr].tex[0] = t1;
            _varray[nr].tex[1] = t2;
            ++nr;
        }
    }

    nr = 0;
    // define indices for all triangles
    for (int i = 1; i <= segments; ++i) {
        for (int j = 0; j < segments; ++j) {
            const int t = segments + 1;
            _iarray[nr] = t * (i - 1) + j + 0; //1
            ++nr;
            _iarray[nr] = t * (i + 0) + j + 0; //2
            ++nr;
            _iarray[nr] = t * (i + 0) + j + 1; //3
            ++nr;

            _iarray[nr] = t * (i - 1) + j + 0; //4
            ++nr;
            _iarray[nr] = t * (i + 0) + j + 1; //5
            ++nr;
            _iarray[nr] = t * (i - 1) + j + 1; //6
            ++nr;
        }
    }
}

Sphere::Sphere(const Sphere& cpy)
    : _vaoID(cpy._vaoID)
    , _vBufferID(cpy._vBufferID)
    , _iBufferID(cpy._iBufferID)
    , _isize(cpy._isize)
    , _vsize(cpy._vsize)
    , _varray(new Vertex[_vsize])
    , _iarray(new int[_isize])
{
    // @TODO This needs to be tested ---abock

    std::memcpy(_varray, cpy._varray, _vsize * sizeof(Vertex));
    std::memcpy(_iarray, cpy._iarray, _isize * sizeof(int));
}

Sphere::~Sphere() {
    delete[] _varray;
    delete[] _iarray;

    _varray = nullptr;
    _iarray = nullptr;

    glDeleteBuffers(1, &_vBufferID);
    glDeleteBuffers(1, &_iBufferID);
    glDeleteVertexArrays(1, &_vaoID);
}

bool Sphere::initialize() {
    // Initialize and upload to graphics card
    if (_vaoID == 0) {
        glGenVertexArrays(1, &_vaoID);
    }

    if (_vBufferID == 0) {
        glGenBuffers(1, &_vBufferID);

        if (_vBufferID == 0) {
            LERROR("Could not create vertex buffer");
            return false;
        }
    }

    if (_iBufferID == 0) {
        glGenBuffers(1, &_iBufferID);

        if (_iBufferID == 0) {
            LERROR("Could not create index buffer");
            return false;
        }
    }

    // First VAO setup
    glBindVertexArray(_vaoID);

    glBindBuffer(GL_ARRAY_BUFFER, _vBufferID);
    glBufferData(GL_ARRAY_BUFFER, _vsize * sizeof(Vertex), _varray, GL_STATIC_DRAW);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), nullptr);

    glEnableVertexAttribArray(1);
    glVertexAttribPointer(
        1,
        2,
        GL_FLOAT,
        GL_FALSE,
        sizeof(Vertex),
        reinterpret_cast<const GLvoid*>(offsetof(Vertex, tex)) // NOLINT
    );

    glEnableVertexAttribArray(2);
    glVertexAttribPointer(
        2,
        3,
        GL_FLOAT,
        GL_FALSE,
        sizeof(Vertex),
        reinterpret_cast<const GLvoid*>(offsetof(Vertex, normal)) // NOLINT
    );

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _iBufferID);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, _isize * sizeof(int), _iarray, GL_STATIC_DRAW);

    glBindVertexArray(0);
    return true;
}

void Sphere::render() {
    glBindVertexArray(_vaoID);  // select first VAO
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _iBufferID);
    glDrawElements(GL_TRIANGLES, _isize, GL_UNSIGNED_INT, nullptr);
    glBindVertexArray(0);
}

}  // namespace openspace