<?php
$pts = array();
for($i=0; $i <= 100; $i+=1){
	$pts[] = $i;
	$pts[] = sqrt($i);
}

draw_graph(1000, 500, 30, $pts, 0, 0, 1, 1);

// $w -- ширина графика
// $h -- высота графика
// $s -- кол-во пикселей в одном делении
// $pts -- массив с точками в формате array(x1, y1, x2, y2, x3, x3, ...), где тч. n(xn, yn)
// $grid -- нарисовать сетку
// $small_grid -- нарисовать сетку, если в делении больше 20 пикселей
// $point -- рисовать точку в месте сгиба
// $point_info -- отобразить рядом с точкой её координаты
function draw_graph($w, $h, $s, $pts, $grid, $small_grid, $point, $point_info){
	$image = imagecreate($w, $h);
	imageantialias($image, true);
	$color_body = imagecolorallocate($image, 0xFF, 0xFF, 0xFF);
	$color_line = imagecolorallocate($image, 0x00, 0x00, 0x00);
	$color_graph = imagecolorallocate($image, 0xFF, 0x00, 0x00);
	$color_grid = imagecolorallocate($image, 0xCC, 0xCC, 0xCC);
	$color_text = imagecolorallocate($image, 0xFF, 0x44, 0x44);
	imagefilledrectangle($image, 0, 0, $w, $h, $color_body);
	$graph_font = 'tahoma.ttf';
	$x0 = $w/2;
	$y0 = $h/2;
	if ($grid){
		for ($i = 0, $j=1; $i < $x0; $i+=$s, $j++){
			$x = $i + $x0;
			$x2 = -$i + $x0;
			imageline($image, $x, 0, $x, $h, $color_grid);
			imageline($image, $x2, 0, $x2, $h, $color_grid);
			if ($small_grid && $s >= 20){
				for ($n = $x+$s/5; $n < $x+$s; $n += $s/5) imageline($image, $n, 0, $n, $h, $color_grid);
				for ($n = $x2-$s/5; $n > $x2-$s; $n -= $s/5) imageline($image, $n, 0, $n, $h, $color_grid);
			}
		}
		for ($i = 0, $j=1; $i < $y0; $i+=$s, $j++){
			$y = -$i + $y0;
			$y2 = $i + $y0;
			imageline($image, 0, $y, $w, $y, $color_grid);
			imageline($image, 0, $y2, $w, $y2, $color_grid);
			if ($small_grid && $s >= 20){
				for ($n = $y-$s/5; $n > $y-$s; $n -= $s/5) imageline($image, 0, $n, $w, $n, $color_grid);
				for ($n = $y2+$s/5; $n < $y2+$s; $n += $s/5) imageline($image, 0, $n, $w, $n, $color_grid);
			}
		}
	}
	$font_size = $s/3;
	if ($font_size < 5 && $s >= 6) $font_size = 5;
	$font = imagettfbbox($font_size, 0, $graph_font, '1');
	$font_height = $font[0]-$font[7];
	$s_half = $s/2;
	for ($i = $s, $j=1; $i < $x0; $i+=$s, $j++){
		$x = $i + $x0;
		$x2 = -$i + $x0;
		imageline($image, $x, $y0-$s_half, $x, $y0+$s_half, $color_line);
		imageline($image, $x2, $y0-$s_half, $x2, $y0+$s_half, $color_line);
		imagettftext($image, $font_size, 0, $x+2, $y0+$font_height+2, $color_line, $graph_font, $j);
		imagettftext($image, $font_size, 0, $x2+2, $y0+$font_height+2, $color_line, $graph_font, '-'.$j);
	}
	for ($i = $s, $j=1; $i < $y0; $i+=$s, $j++){
		$y = -$i + $y0;
		$y2 = $i + $y0;
		imageline($image, $x0-$s_half, $y, $x0+$s_half, $y, $color_line);
		imageline($image, $x0-$s_half, $y2, $x0+$s_half, $y2, $color_line);
		imagettftext($image, $font_size, 0, $x0+3, $y-3, $color_line, $graph_font, $j);
		imagettftext($image, $font_size, 0, $x0+3, $y2-3, $color_line, $graph_font, '-'.$j);
	}
	imageline($image, $x0, 0, $x0, $h, $color_line);
	imageline($image, 0, $y0, $w, $y0, $color_line);
	imageline($image, $x0-$s_half, $s_half, $x0, 0, $color_line);
	imageline($image, $x0, 0, $x0+$s/2, $s/2, $color_line);
	imageline($image, $w-$s_half, $y0-$s_half, $w, $y0, $color_line);
	imageline($image, $w-$s_half, $y0+$s_half, $w, $y0, $color_line);
	$font_size = $s*0.75;
	if ($font_size < 6) $font_size = 6;
	$font = imagettfbbox($font_size, 0, $graph_font, 'x');
	imagettftext($image, $font_size, 0, $x0+$s+3, 2+$font_size, $color_line, $graph_font, 'y');
	imagettftext($image, $font_size, 0, $w-3-($font[2] - $font[0]), $y0+$s_half+($font[0]-$font[7])+3, $color_line, $graph_font, 'x');

	$x_last = $pts[0]*$s + $x0;
	$y_last = -$pts[1]*$s + $y0;
	$font_size = $s/4;
	$font = imagettfbbox($font_size, 0, $graph_font, 'X');
	$font_height = $font[0] - $font[7];
	$s_10 = $s/10;
	if ($font_size < 5) $font_size = 5;
	for ($i=1; $i <= count($pts); $i+=2){
		$x = $pts[$i-1]*$s + $x0;
		$y = -$pts[$i]*$s + $y0;
		imageline($image, $x_last, $y_last, $x, $y, $color_graph);
		if ($point) imagefilledrectangle($image, $x-$s_10, $y-$s_10, $x+$s_10, $y+$s_10, $color_graph);
		if ($point_info){
			$text = '('.bcdiv($pts[$i-1], 1, 2).'; '.bcdiv($pts[$i], 1, 2).')';
			imagettftext($image, $font_size, 0, $x+$s_10-1, $y+$s_10+$font_height, $color_body, $graph_font, $text);
			imagettftext($image, $font_size, 0, $x+$s_10+1, $y+$s_10+$font_height, $color_body, $graph_font, $text);
			imagettftext($image, $font_size, 0, $x+$s_10, $y+$s_10+$font_height+1, $color_body, $graph_font, $text);
			imagettftext($image, $font_size, 0, $x+$s_10, $y+$s_10+$font_height-1, $color_body, $graph_font, $text);

			imagettftext($image, $font_size, 0, $x+$s_10, $y+$s_10+$font_height, $color_text, $graph_font, $text);
		}
		$x_last = $x;
		$y_last = $y;
	}
	header("Content-type: image/gif");
	imagegif($image);
	imagedestroy($image);
}

?>