#include <stdlib.h>
#include <string.h>
#include <GL/glut.h>

#define X1  -1.0
#define X2  1.0
#define Y1  -1.0
#define Y2  1.0

#define display display_obj

static GLfloat vbuf[] = {X1, Y1, 0, X1, Y2, 0, X2, Y2, 0, X2, Y1, 0};

void 
display_normal(void)
{
        GLuint lid;

        glClear(GL_COLOR_BUFFER_BIT);
        glColor3f (0.0, 0.0, 1.0);

        glVertexPointer (3, GL_FLOAT, 0, vbuf);
        glEnableClientState (GL_VERTEX_ARRAY);

        lid = glGenLists(1);
        glNewList(lid, GL_COMPILE);
        glDrawArrays(GL_LINE_LOOP, 0, 4);
        glEndList();
        glCallList(lid);
        glDeleteLists(lid, 1);

        glFlush();
}

void display_obj(void)
{
        GLuint id = 0;
        GLuint lid = 0;

        glClear(GL_COLOR_BUFFER_BIT);
        glColor3f (0.0, 0.0, 1.0);

        glGenBuffers(1, &id);
        glBindBuffer(GL_ARRAY_BUFFER, id);
        glBufferData(GL_ARRAY_BUFFER, sizeof(vbuf), vbuf, GL_STATIC_DRAW);

        glVertexPointer(3, GL_FLOAT, 0, 0);
        glEnableClientState(GL_VERTEX_ARRAY);

#if 0
        glDrawArrays(GL_LINE_LOOP, 0, 4); /* DrawArrays outside a display list is OK */
#else
        /* DrawArrays within a display list causes a segment fault */
        lid = glGenLists(1);
        glNewList(lid, GL_COMPILE);
        glDrawArrays(GL_LINE_LOOP, 0, 4);
        glEndList();
        glCallList(lid);
        glDeleteLists(lid, 1);
#endif

        glDeleteBuffers(1, &id);
        glFlush();
        
}


static void
key(unsigned char k, int x, int y)
{
        switch (k) {
        case 27:
                exit(0);
                break;
        default:
                return;
        }
        glutPostRedisplay();
}


static void 
reshape(int width, int height)
{
        float ar = (float)width / (float)height + 2.0;
        glViewport(0, 0, width, height);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluOrtho2D (-ar, ar, -ar, ar);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
}

int 
main(int argc, char** argv)
{
        glutInit(&argc, argv);
        glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
        glutInitWindowSize(250, 250);
        glutInitWindowPosition(100, 100);
        glutCreateWindow("Buffer Objects");
        glutReshapeFunc(reshape);
        glutDisplayFunc(display);
        glutKeyboardFunc(key);
        glutMainLoop();
        return 0;
}