/*--------------------------------------------------*
*Open a window on the XFree86 system and draw to it.*
*Created by Robbie Dave after learning about Xlib.h *
*---------------------------------------------------*
Compile with: gcc -o dave dave.c -L/usr/X11R6/lib -lX11
*/

// Include the Xlib.h file so as to use X functions.
#include <X11/Xlib.h>
#define NIL (0)       // A name for the void pointer
//This is the 'main' function in c programs.
int main(void) { 

// Initialise the variables.
Window win;
int win_width = 640;
int win_height = 480;
int win_x;
int win_y;
int screen_num;
GC gc;
XImage *xi=NULL; 
XColor system_color_1; 
XColor exact_color;
Colormap davescol;
int x; 
int y; 
int c;

// Get a pointer (*display) to the X display.
Display *display = XOpenDisplay(NIL);

/*
Obtain the screen number using our *display pointer.
The display pointer does not need the asterisk (*).
*/
screen_num = DefaultScreen(display);

/*
Now we have the screen number and display pointer,
we get the GC (graphics context) of the X system.
*/
gc = DefaultGC(display, screen_num); 

// I assume these are the window offsets set to 0.
win_x = win_y = 0;

// Create the window
win = XCreateSimpleWindow(display, RootWindow(display, screen_num), win_x, win_y, win_width, win_height, 0, BlackPixel(display, screen_num), BlackPixel(display, screen_num));

//Make the screen appear and flush events.
XMapWindow(display, win); 
XFlush(display); 

// Capture the screen for drawing.
xi = XGetImage(display, win, 0,0, win_width, win_height, AllPlanes, ZPixmap); 

//Obtain a colormap to get colors.
davescol = DefaultColormap(display, screen_num); 

// Enter a color into the colormap to use later.
Status rc = XAllocNamedColor(display, davescol, "red", &system_color_1, &exact_color);

	//These two x, y for loops used to plot pixels to window.
	for (x = 0; x < win_width; x++) 
		{ 
		for(y = 0; y < win_height; y++) 
			{
			//Plot a pixel. 
			XPutPixel(xi, x, y, exact_color.pixel);
			/*Experiement with the x, y formula
			for different animations.
			*/
			exact_color.pixel = ((x*x)+(y*y))*0.05;

			if (exact_color.pixel > 65535) 
			{exact_color.pixel=65535;}
			}
	
	}

//This for loop is used for animation.
for(c = 8; c < 64; c++) 
	{ 
	//Animate the colors
	XAddPixel(xi, c);
	//Try to control the animation.
	XFlush(display);
	XSync(display, 1);

	/*
	After plotting to every pixel in the window,
	actually display what you've drawn.
	*/
XPutImage(display, win, gc, xi, 0, 0, 0, 0, win_width, win_height); 
	}

//Clean up the memory a bit, but not much.
XDestroyImage(xi);
XCloseDisplay(display); 
return (0);
}