Creating arrays using for loops in OpenGL - c++

Question

What I have to do is create a square that is made up of 8 triangles, all the same size, using arrays. The coordinates of the four corners of the square are, (-10, -10, 10), (-10, -10, -10), (10, -10, -10), (10, -10, 10). And that's starting with the upper left and going counter clockwise.
I have already created it before just entering values into the array but now I have to figure out how to do it using for loops in C++. So I know that for each array (I need to create a vertex, index and color array) I need to create a for loop and that that for loop has to have a for loop inside of it.

Answer 1

I like to use Eigen::Vector2f for Vec but anything with a similar interface should work:
template< typename Vec >
void glVec2d( const Vec& vec )
{
glVertex2d( vec.x(), vec.y() );
}
template< typename Vec >
void glTex2d( const Vec& vec )
{
glTexCoord2d( vec.x(), vec.y() );
}
template< typename Vec >
void glQuad2d
(
const Vec& A, // lower left coord
const Vec& B, // lower right coord
const Vec& C, // upper right coord
const Vec& D, // upper left coord
unsigned int divs = 2,
const Vec& At = Vec(0,0),
const Vec& Bt = Vec(1,0),
const Vec& Ct = Vec(1,1),
const Vec& Dt = Vec(0,1)
)
{
// base case
if( divs == 0 )
{
glTex2d( At );
glVec2d( A );
glTex2d( Bt );
glVec2d( B );
glTex2d( Ct );
glVec2d( C );
glTex2d( Dt );
glVec2d( D );
return;
}
Vec AB = (A+B) * 0.5;
Vec BC = (B+C) * 0.5;
Vec CD = (C+D) * 0.5;
Vec AD = (A+D) * 0.5;
Vec ABCD = (AB+CD) * 0.5;
Vec ABt = (At+Bt) * 0.5;
Vec BCt = (Bt+Ct) * 0.5;
Vec CDt = (Ct+Dt) * 0.5;
Vec ADt = (At+Dt) * 0.5;
Vec ABCDt = (ABt+CDt) * 0.5;
// subdivided point layout
// D CD C
//
// AD ABCD BC
//
// A AB B
// subdivide
glQuad2d( A, AB, ABCD, AD, divs - 1, At, ABt, ABCDt, ADt );
glQuad2d( AB, B, BC, ABCD, divs - 1, ABt, Bt, BCt, ABCDt );
glQuad2d( ABCD, BC, C, CD, divs - 1, ABCDt, BCt, Ct, CDt );
glQuad2d( AD, ABCD, CD, D, divs - 1, ADt, ABCDt, CDt, Dt );
}
It's currently recursive but you could always add an explicit stack for some for-loop action.