Arches (2D or 3D) in OpenGL - c++

Question

I am trying to draw the shape shown below (in black) in OpenGL (for desktops, not mobile). I'd prefer it in 3D, but 2D would suffice as well. I will be mapping a texture to it as well. I've used triangle fans/strips for other things in the past and I imagine that's what I'd need to use here but I'm just not sure where to start on it. I've drawn the WHITE part before, but never the inverse (the black part). Any thoughts or guidance on what to use (triangle fan, triangle strip, some other odd OpenGL shape I probably didn't know existed, etc...)
Final Solution:
void draw_arch(GLfloat width, GLfloat height, GLint slices)
{
glPushMatrix();
GLfloat offset = 0.5f;
glScalef(width/2,height/(1+offset),1.0f);
glBegin(GL_QUADS);
for( unsigned int i = 0; i < slices; ++i ) {
float curAngle = ( ( i + 0 ) / (float)slices ) * 3.14159;
float nxtAngle = ( ( i + 1 ) / (float)slices ) * 3.14159;
glVertex2f( cos( curAngle ), sin( curAngle ) );
glVertex2f( cos( curAngle ), 1.0f + offset );
glVertex2f( cos( nxtAngle ), 1.0f + offset );
glVertex2f( cos( nxtAngle ), sin( nxtAngle ) );
}
glEnd();
glPopMatrix();
}
I can adjust the "offset" variable to make different looking arches, however in this application, I choose 0.5 to make it look the way I wanted it to!

Answer 1

Generate the top half of a circle and an offset above it and link the two with quads/triangles:
#include <GL/glut.h>
#include <cmath>
void glShape( const float height, unsigned int segs )
{
glBegin( GL_QUADS );
for( unsigned int i = 0; i < segs; ++i )
{
float curAngle = ( ( i + 0 ) / (float)segs ) * 3.14159;
float nxtAngle = ( ( i + 1 ) / (float)segs ) * 3.14159;
glVertex2f( cos( curAngle ), sin( curAngle ) );
glVertex2f( cos( curAngle ), 1 + height );
glVertex2f( cos( nxtAngle ), 1 + height );
glVertex2f( cos( nxtAngle ), sin( nxtAngle ) );
}
glEnd();
}
void display()
{
glClearColor( 0, 0, 0, 1 );
glClear( GL_COLOR_BUFFER_BIT );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
double w = glutGet( GLUT_WINDOW_WIDTH );
double h = glutGet( GLUT_WINDOW_HEIGHT );
double ar = w / h;
glOrtho( -2 * ar, 2 * ar, -2, 2, -1, 1 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3ub( 255, 0, 0 );
glShape( 0.1f, 20 );
glutSwapBuffers();
}
int main( int argc, char **argv )
{
glutInit( &argc, argv );
glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
glutInitWindowSize( 640, 480 );
glutCreateWindow( "GLUT" );
glutDisplayFunc( display );
glutMainLoop();
return 0;
}
Probably not the minimal number of quads/triangles but it's quick and easy :)