#include <stdlib.h>
#include <math.h>
#include "SDL.h"
#include "time.h"

#define WINDOW_WIDTH  640
#define WINDOW_HEIGHT 480

SDL_Surface *screen;

int g_aPalette[256];

int g_aFunction1[WINDOW_WIDTH + 628][WINDOW_HEIGHT];
int g_aFunction2[WINDOW_WIDTH][WINDOW_HEIGHT];

float g_fF1Tick;
float g_fF2Tick;
float g_fPaletteTick;


inline bool PlotPixel(int x, int y, int color)
{
	if(x < 0 || y < 0 || x > WINDOW_WIDTH -1 || y > WINDOW_HEIGHT -1)
		return false;

	((unsigned int*)screen->pixels)[y * WINDOW_WIDTH + x] = color;

	return true;
}


void render()
{   
	// Lock surface if needed
	if (SDL_MUSTLOCK(screen)) 
		if (SDL_LockSurface(screen) < 0) 
			return;

	// Clear screen
	SDL_FillRect(screen, NULL, SDL_MapRGB(screen->format, 0, 0, 0));


	// Draw stars
	int x, y, color;
	for(x = 0; x < WINDOW_WIDTH; x++)
		for(y = 0; y < WINDOW_HEIGHT; y++)
		{
			color = g_aFunction1[x + (int)g_fF1Tick][y] + g_aFunction2[x][y];
			PlotPixel(x, y, g_aPalette[(color + (int)g_fPaletteTick) % 256]);
		}


	// Unlock if needed
	if (SDL_MUSTLOCK(screen)) 
		SDL_UnlockSurface(screen);

	// Tell SDL to update the whole screen
	SDL_UpdateRect(screen, 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);  
}

void tick()
{
	// Ask SDL for the time in milliseconds
	static int lastTick = SDL_GetTicks() - 100;
	int iDelta = SDL_GetTicks() - lastTick;
	lastTick = SDL_GetTicks();

	if(iDelta > 33)
		iDelta = 33;

	g_fPaletteTick += iDelta / 6.0f;
	g_fF1Tick += iDelta / 10.0f;


	g_fF1Tick = fmod(g_fF1Tick, 628);

}


// Entry point
int main(int argc, char *argv[])
{
//	srand((unsigned)time(NULL));

	// Initialize SDL's subsystems - in this case, only video.
	if(SDL_Init(SDL_INIT_VIDEO) < 0)
	{
		fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
		exit(1);
	}

	// Register SDL_Quit to be called at exit; makes sure things are
	// cleaned up when we quit.
	atexit(SDL_Quit);

	// Attempt to create a 640x480 window with 32bit pixels.
	screen = SDL_SetVideoMode(WINDOW_WIDTH, WINDOW_HEIGHT, 32, SDL_SWSURFACE);

	// If we fail, return error.
	if(!screen)
	{
		fprintf(stderr, "Unable to set video: %s\n", SDL_GetError());
		exit(1);
	}


	g_fPaletteTick = 0.0f;

	
	int x, y;

	// Create the function tables
	for(x = 0; x < WINDOW_WIDTH + 628; x++)
		for(y = 0; y < WINDOW_HEIGHT; y++)
			g_aFunction1[x][y] = (((sin((float)x * 0.05f) + 1.0f) * 128) + ((sin((float)y * 0.05f) + 1.0f) * 128)) / 2;

	for(x = 0; x < WINDOW_WIDTH; x++)
		for(y = 0; y < WINDOW_HEIGHT; y++)	
			g_aFunction2[x][y] = int(128.0 + (128.0 * sin(sqrt((x - WINDOW_WIDTH / 2.0) * 
											 (x - WINDOW_WIDTH / 2.0) + (y - WINDOW_HEIGHT / 2.0) * 
											 (y - WINDOW_HEIGHT / 2.0)) / 8.0))) / 2;


	// Create the palette
	int r, g, b;
	float pi = 3.1415f;
	for(int i = 0; i < 256; i++)
    {
        r = (int)(128 * (sin(pi * i / 127.0f) + 1.0f));
        g = (int)(128 * (sin(pi * i / 63.0f) + 1.0f)) * (r / 256.0f);
        b = 0;

        g_aPalette[i] = (r << 16) + (g << 8) + b;
    } 
	


	// Main loop: loop forever.
	while(true)
	{
		// Tick stuff;
		tick();

		// Render stuff
		render();

		// Poll for events, and handle the ones we care about.
		SDL_Event event;
		while (SDL_PollEvent(&event)) 
		{
			switch (event.type) 
			{
			case SDL_KEYDOWN:
				break;
			case SDL_KEYUP:
				// If escape is pressed, return (and thus, quit)
				if(event.key.keysym.sym == SDLK_ESCAPE)
					return 0;
				break;
				
			case SDL_QUIT:
				return 0;
			}
		}
	}
	return 0;
}