Modern OpenGL : Draw a sphere and cylinder

Question

I\'ve learned how to draw a cube using OpenGL from various tutorials.

For a cube, we consider each face to be composed of two triangles, and then appropriately set up th

Answer 1

Here is some code that I use when drawing spheres.

Note: This code uses C++, with the GLM math library.

// Calc The Vertices
for (int i = 0; i <= Stacks; ++i){

    float V   = i / (float) Stacks;
    float phi = V * glm::pi <float> ();

    // Loop Through Slices
    for (int j = 0; j <= Slices; ++j){

        float U = j / (float) Slices;
        float theta = U * (glm::pi <float> () * 2);

        // Calc The Vertex Positions
        float x = cosf (theta) * sinf (phi);
        float y = cosf (phi);
        float z = sinf (theta) * sinf (phi);

        // Push Back Vertex Data
        vertices.push_back (glm::vec3 (x, y, z) * Radius);
    }
}

// Calc The Index Positions
for (int i = 0; i < Slices * Stacks + Slices; ++i){

    indices.push_back (i);
    indices.push_back (i + Slices + 1);
    indices.push_back (i + Slices);

    indices.push_back (i + Slices + 1);
    indices.push_back (i);
    indices.push_back (i + 1);
}

This algorithm creates what is called a UV Sphere. The 'Slices' and 'Stacks' are the number of subdivisions on the X and Y axis.

Answer 2

For cylinders, it is convenient to work in cylindrical coordinates: (angle, radius, height). You will compute two polygons (constant angle increment, fixed radius, two height values) and create: two sets of triangles for the basis and a set of rectangles (split in two) for the lateral surface.

For spheres, you will use spherical coordinates: (inclination, elevation, radius). By varying the two angles (one at a time), you will describe parallels and meridians on the sphere. These define a meshing, such that every tile is a quadrilateral (except at the poles); split along a diagonal to get triangles.