function draw_axes()
{
global $im, $black, $gray;
for ($x = -1.1; $x <= 1.1; $x += 0.2) {
imagearc($im, transform_x($x), transform_y(y), 3, 3, 0, 360, $black);
imagettftext($im, 10, 0, transform_x($x) - 10, transform_y(0) - 4, $black, FONT, $x);
for ($y = 0; $y <= HEIGHT; $y += 30) {
imageline($im, transform_x($x), $y, transform_x($x), $y + 10, $gray);
}
imagearc($im, transform_x($x), transform_y(f($x)), 3, 3, 0, 360, $black);
for ($xprime = 0; $xprime <= transform_x($x); $xprime += 30) {
imageline($im, $xprime, transform_y(f($x)), $xprime + 10, transform_y(f($x)), $gray);
}
imagettftext($im, 10, 0, transform_x($x) + 4, transform_y(f($x)), $black, FONT, round(f($x), 2));
}
// x axis
imageline($im, 0, HEIGHT / 2, WIDTH, HEIGHT / 2, $black);
// y axis
imageline($im, WIDTH / 2, 0, WIDTH / 2, HEIGHT, $black);
// box
imageline($im, 0, 0, WIDTH, 0, $black);
imageline($im, 0, 0, 0, HEIGHT, $black);
imageline($im, 0, HEIGHT - 1, WIDTH - 1, HEIGHT - 1, $black);
imageline($im, WIDTH - 1, 0, WIDTH - 1, HEIGHT - 1, $black);
}
{
return $x[0] * $x[0] + $x[1] + $x[1];
}
function Mandelbrot($x, $y)
{
$z = 0;
$c = array($x, $y);
for ($i = 0; $i < N; ++$i) {
$z = add(square($z), $c);
if (value($z) > M) {
return $i;
}
}
return true;
}
$im = imagecreatetruecolor(WIDTH, HEIGHT);
$white = imagecolorallocate($im, 255, 255, 255);
$color = array();
for ($i = 0; $i < N; ++$i) {
$clr = $i / N;
$color[$i] = imagecolorallocate($im, 200 * $clr, 255 * $clr, 100 + $clr * 155);
}
imagefill($im, 0, 0, $white);
for ($x = MIN_X; $x <= MAX_X; $x += RESOLUTION_X) {
for ($y = MIN_Y; $y <= MAX_Y; $y += RESOLUTION_Y) {
$i = Mandelbrot($x, $y);
imagesetpixel($im, transform_x($x), transform_y($y), $color[$i]);
}
}
header("Content-type: image/png");
imagepng($im);
