// 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 // Provides istream, ostream and ofstream types #include // 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円0円0円0円", 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円'); // Non-interleaved image // Code size (with 128 colors, pixels are 7 bits each). out.put('7円'); // 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円', '000円', '000円' }, // BLACK {'100円', '100円', '100円' }, // DARKGRAY {'300円', '300円', '300円' }, // LIGHTGRAY {'250円', '000円', '000円' }, // RED {'000円', '250円', '000円' } // 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円'); gif.write("200円", 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円'); // Block byte count gif.put('201円'); // End code for 8-bit codes gif.put('0円'); // Data Terminator gif.put('73円'); // GIF File Terminator gif.close( ); } }