Tutorial on Index Buffers

When using DrawElements with GL_TRIANGLE_STRIP or GL_LINE_STRIP you have to specify (1) a buffer of positions and (2) a buffer of indices:

std::vector<vec3> vpoints;
std::vector<unsigned int> indices;

Assume you have a 3x3 meshed grid, as follows:

     0     1     2
     3     4     5
     6     7     8

In vpoints you (programmatically: for-loop) insert the vertex positions of your grid:

vpoints[0] = vec3(-1, -1);
vpoints[1] = vec3( 0, -1);  
vpoints[2] = vec3(+1, -1);  
...
vpoints[8] = vec3(+1, +1);

Similarly, you will programmatically fill-in the indices of your grid. Indices for the first row (and a bit of the second) will look as follows:

indices = [0, 3, 1, 4, 2, 5, RESTART_ID, 3, 6, 4, 7, 5, 8]