// A display list is an object created that can be called multiple
// times without OpenGL having to recreate the object again and 
// again. This saves processing time and thus increases your frames
// per second when you move into worlds with many objects.

// A display list can be treated just like any other object, you
// can change its texture, lighting abilities, size, etc.

// Although once the list has been created you cannot edit
// the actual shape of the object in the list. You can scale it
// with the scale command, but you cannot change the vertices etc
// without recreating the whole list from scratch.

// Now to create a list we first have to setup and unsigned integer
// to hold the list. I have done it with:
// GLuint cubelist; 

// next we move onto acctually creating the list. When doing this
// there are 2 steps. The first is to set the list the generate a list
// with:
// cubelist = glGenLists(1);

// then we tell it to make a new list using cubelist:
// glNewList(cubelist,GL_COMPILE);

// after this come whatever code you need for your object.

// then after you have done all the code you need for your object
// to function, just call:
// glEndList();
// to end the creation of the current active list.

// and to call the list whenever you need it, you simply use
// glCallList(cubelist);

// and that is it, just remember to create the list before you call it
// otherwise nothing will show.

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

GLuint cubelist; //we are going to hold our list in here

//create the cube display list
void createcube (void) {
	cubelist = glGenLists(1); //set the cube list to Generate a List
	glNewList(cubelist,GL_COMPILE); //compile the new list
	glPushMatrix();
	glutSolidCube(2); //draw the cube
	glPopMatrix();
	glEndList(); //end the list
}

void init (void) {
	glEnable (GL_DEPTH_TEST); //enable the depth testing
	glEnable (GL_LIGHTING); //enable the lighting
	glEnable (GL_LIGHT0); //enable LIGHT0, our Diffuse Light
	glShadeModel (GL_SMOOTH); //set the shader to smooth shader
	createcube(); //call the command to create the cube
}

void display (void) {
	glClearColor (0.0,0.0,0.0,1.0); //clear the screen to black
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //clear the color buffer and the depth buffer
    glLoadIdentity();  
	glTranslatef(0,0,-5);
	glCallList(cubelist); //call the cube list
	glutSwapBuffers(); //swap the buffers
}

void reshape (int w, int h) {
	glViewport (0, 0, (GLsizei)w, (GLsizei)h); //set the viewport to the current window specifications
	glMatrixMode (GL_PROJECTION); //set the matrix to projection
	glLoadIdentity ();
	gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0); //set the perspective (angle of sight, width, height, , depth)
	glMatrixMode (GL_MODELVIEW); //set the matrix back to model
}

void keyboard (unsigned char key, int x, int y) {
	if (key==27)
	{
	glutLeaveGameMode(); //set the resolution how it was
	exit(0); //quit the program
	}
}

int main (int argc, char **argv) {
    glutInit (&argc, argv);
	glutInitDisplayMode (GLUT_DOUBLE | GLUT_DEPTH); //set the display to Double buffer, with depth
	glutGameModeString( "1024x768:32@75" ); //the settings for fullscreen mode
	glutEnterGameMode(); //set glut to fullscreen using the settings in the line above
	init (); //call the init function
    glutDisplayFunc (display); //use the display function to draw everything
	glutIdleFunc (display); //update any variables in display, display can be changed to anyhing, as long as you move the variables to be updated, in this case, angle++;
	glutReshapeFunc (reshape); //reshape the window accordingly
	glutKeyboardFunc (keyboard); //check the keyboard
    glutMainLoop (); //call the main loop
    return 0;
}