/*
NOTE:

1. This program is to create a window and...
2. Clear the area of that window with some color
*/


# include <GL/glut.h>


void ClearWindow(void)
{
    // What ever color we see, it is a combination of red, green and blue
    // for black  ==> red = green = blue = 0.0
    // for white  ==> red = green = blue = 1.0
    // for yellow ==> red = green = 1.0, blue = 0.0

    // play with these values and see how the output changes
    // min value = 0.0 & max value is 1.0
    float red = 1.0;
    float green = 1.0;
    float blue = 0.0;

    float opacity = 1.0;
    // No.. it is not the opacity of the window
    // opacity is also called as alpha.
    // If you know alpha but not opacity of a window - I'm sorry for the extra confusion
    // If you know none - Don't worry; just ignore them
    // If you know both - why the hell are you reading this? read GPU GEMS instead
 
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    // OK : Let's call some functions - enough with these variables
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~     
    // tell to opengl that we want this color combination 
    // to be stored as the clear color
    glClearColor(red, green, blue, opacity);

    // since opengl knows what is the color to be used to clear the window,
    // we can tell opengl to clear the color buffer "NOW"
    glClear(GL_COLOR_BUFFER_BIT);

    // YES.. there are other buffers as well.
    // and buffer is a memory block where data is stored.
    // For more information on buffers,
    // make sure that you read my "Introduction to Computer Graphics"
    // which is in my "To do list" as on... 24th Sep 2010 (the day when I wrote this)
    // I'm not sure when/if it will be completed
    // or if it is already comleted by the time you read this
    // Will clean up the comments as well once I'm done with all the tutorials
    // As of now, I'm yet to start that tutorial.
    // So... don't ask me what a color buffer is
}


int main(int argc, char** argv)
{
    const int left   = 100;
    const int top    = 100;
    const int width  = 256;
    const int height = 256;

    const char* windowTitle = "I'm back";

    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(width, height); 
    glutInitWindowPosition(left, top);
    glutCreateWindow(windowTitle);

    //NEW FUNCTION in this tutorial's main function
    glutDisplayFunc(ClearWindow); 

    glutMainLoop();

    return 0;
}


/*
Exercise:

Accept command line option to select the clear color.

eg: ./a.out yellow

should change the clear color to yellow
*/


//
//                        MORAL of this tutorial:
//                       ~~~~~~~~~~~~~~~~~~~~~~~~
// The best way to lead a happy life is to ignore as much as you can
//