OpenGL: Why this white scrreen - c++

Question

Why I am getting a full White colored window as an output of this program
Expected a box
code is here
#include<Gl/glut.h>
static GLfloat vertices[] = {0.0, 0.0, 0.0,
0.5, 0.0, 0.0,
0.5, 0.5, 0.0,
0.0, 0.5, 0.0,
};
void reshape(int w, int h)
{
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 0.0);
}
void Draw()
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0,1.0,1.0);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer(3, GL_FLOAT, 0, 0);
glBegin(GL_LINES);
glArrayElement(0);
glArrayElement(1);
glArrayElement(2);
glArrayElement(3);
glEnd();
glDisableClientState(GL_VERTEX_ARRAY);
glFlush();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
glutInitWindowSize(400,400);
glutInitWindowPosition(100,100);
glutCreateWindow("vectors");
glClearColor(0.0,0.0,0.0,0.0);
glutReshapeFunc(reshape);
glutDisplayFunc(Draw);
glutMainLoop();
}
Corrected GL_LINES to GL_QUADS

Answer 1

Multiple problems:
reshape() is broken; glOrtho() multiples by the current matrix and will give nonsensical results if you resize the window more than once.
You request a double-buffered (GLUT_DOUBLE) context but fail to swap the buffers. glFlush() is insufficient. Try glutSwapBuffers() instead.
You really ought to reset your projection/modelview matrices each frame. Helps prevent errors.
Give this a shot:
#include<Gl/glut.h>
static GLfloat vertices[] =
{
0.0, 0.0,
0.5, 0.0,
0.5, 0.5,
0.0, 0.5,
};
void Draw()
{
glClearColor(0.0,0.0,0.0,0.0);
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
glOrtho( -2, 2, -2, 2, -1, 1 );
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glColor3f(1.0,1.0,1.0);
glEnableClientState(GL_VERTEX_ARRAY);
glVertexPointer( 2, GL_FLOAT, 0, vertices );
glBegin(GL_QUADS);
glArrayElement(0);
glArrayElement(1);
glArrayElement(2);
glArrayElement(3);
glEnd();
glDisableClientState(GL_VERTEX_ARRAY);
glutSwapBuffers();
}
int main(int argc, char **argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA);
glutInitWindowSize(400,400);
glutInitWindowPosition(100,100);
glutCreateWindow("vectors");
glutDisplayFunc(Draw);
glutMainLoop();
}

Answer 2

I suspect the problem is your call to glVertexPointer(). The last parameter is supposed to be a pointer to the start of the array you're using, but at the moment you're just passing it a null pointer, so it's got nothing to work with.
Try this instead:
glVertexPointer(3, GL_FLOAT, 0, vertices);
EDIT: By the way, your code won't give you a box. If it works, I think it'll just give you two lines. Try using GL_QUADS instead of GL_LINES.

Answer 3

The main thing that pops out at me is the array:
//static GLfloat vertices[] = {0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.5, 0.5, 0.0, 0.0, 0.5, 0.0, };
should be
static GLfloat vertices[] = {0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.5, 0.5, 0.0, 0.0, 0.5, 0.0 };
(note the removed comma)
Next thing is the enabling and disabling of the client state: that could be done in the main loop for example as it is expensive to enable and disable and your draw loop will suffer because of it.