// FILE: polygif.cxx
// This file implements one non-member function (make_gif) for the polynomial
// class. The implementation does not use compression and other features of
// GIF files.

#include "poly1.h"        // Provides polynomial class definition
#include <fstream>        // Provides istream, ostream and ofstream types
#include <cassert>        // Provides assert
using namespace std;      // All the above items are in the std namespace

namespace main_savitch_4
{
    //   void make_gif(
    //     const polynomial& p,
    //     const char filename[ ],
    //     double low_x,
    //     double high_x,
    //     double low_y,
    //     double high_y
    //     )
    //     PRECONDITION: filename is a legal filename for a gif file.
    //     Also (low_x < high_x) && (low_y < high_y).
    //     POSTCONDITION: A gif file has been written to the specified filename
    //     with a graphical representation of the polynomial in the specified
    //     ranges (low_x...high_x and low_y...high_y).

    void write_gif_header128(
	ostream& out,
	int width,
	int height,
	const unsigned char color_table[128][3]
	)
    {
	// GIF signature and screen descriptor:
	out.write("GIF87a", 6);         // GIF signature
	out.put(width & 0xFF);          // Low byte of screen width
	out.put((width >> 8) & 0xFF);   // High byte of screen width
	out.put(height & 0xFF);         // Low byte of screen width
	out.put((height >> 8) & 0xFF);  // High byte of screen width
	out.put(0xE6);                  // 7-bits per pixel
	out.put(0);                     // Background color
	out.put(0);                     // Zero marks end of screen descriptor

	// Color table:
	out.write(color_table[0], 128*3);

	// Image descriptior:
	out.put(',');                   // Image separator character
	out.write("\0\0\0\0", 4);       // Image starts at 0,0
	out.put(width & 0xFF);          // Low byte of image width
	out.put((width >> 8) & 0xFF);   // High byte of image width
	out.put(height & 0xFF);         // Low byte of image width
	out.put((height >> 8) & 0xFF);  // High byte of image width
	out.put('\0');                  // Non-interleaved image

	// Code size (with 128 colors, pixels are 7 bits each).
	out.put('\7'); // Code size (7-bit data for each pixel).
    }

    void make_gif(
	const polynomial& p,
	const char filename[ ],
	double low_x,
	double high_x,
	double low_y,
	double high_y
	)
    {
	enum color { BLACK = 0, DARKGRAY, LIGHTGRAY, RED, GREEN };
	const unsigned char COLOR_TABLE[128][3] = {
	    {'\000', '\000', '\000' },  // BLACK
	    {'\100', '\100', '\100' },  // DARKGRAY
	    {'\300', '\300', '\300' },  // LIGHTGRAY
	    {'\250', '\000', '\000' },  // RED
	    {'\000', '\250', '\000' }   // GREEN
	};
	
	const int SIZE  = 300; // Gif map width and height
	
	double delta_x = (high_x - low_x) / (SIZE - 1);
	double delta_y   = (high_y - low_y) / (SIZE - 1);
	bool vertical_axis, horizontal_axis;
	int row, column;
	double current_x, current_y;
	double nearness;
	double value[SIZE];
	char color;
	
	// Check that the file opened okay and write the front 
        // information to the file.
	ofstream gif(filename, ios::out|ios::binary);
	assert(gif);
	
	write_gif_header128(gif, SIZE, SIZE, COLOR_TABLE);
    
	// Compute the value of the function at each column
	for (column = 0; column < SIZE; column++)
	    value[column] = p.eval(low_x + column * delta_x);

	// Write the pixel data for the picture
	for (row = SIZE-1; row >= 0; --row)
	{
	    current_y = low_y + row * delta_y;
	    horizontal_axis = (delta_y >= current_y) && (current_y > -delta_y);
	    for (column = 0; column < SIZE; ++column)
	    {
		if ((column % 5) == 0)
		{
		    gif.put('\6');
		    gif.write("\200", 1); // Start code for 8-bit codes
		}
		current_x = low_x + column * delta_x;
		vertical_axis= (delta_x >= current_x) && (current_x > -delta_x);
		nearness = current_y - value[column];
		if ((delta_y >= nearness) && (nearness >= -delta_y))
		    color = BLACK;
		else if (vertical_axis || horizontal_axis)
		    color = DARKGRAY;
		else if ((current_y < value[column]) && (current_y >= 0))
		    color = GREEN;
		else if ((current_y > value[column]) && (current_y < 0))
		    color = RED;
		else
		    color = LIGHTGRAY;
		
		gif.put(color);
	    }
	}
	
	// Write the GIF ending and close the file
	gif.put('\1');      // Block byte count
	gif.put('\201');    // End code for 8-bit codes
	gif.put('\0');      // Data Terminator
	gif.put('\73');     // GIF File Terminator
	gif.close( );
    }

}