Changing the center of rotation of Imagerotate - php

Question

Imagerotate rotates the image using the given angle in degrees.
The center of rotation is the center of the image, and the rotated image may have different dimensions than the original image.
How do I change the center of rotation to coordinate x_new and y_new and avoid automatic resizing?
Example: Rotation around red dot.

Answer 1

First idea that comes to mind is to move the image so that its new center is at x_new, y_new rotate it and move back.
assumptions:
0 < x_new < w
0 < y_new < h
Pseudocode:
new_canter_x = MAX(x_new, w - x_new)
new_center_y = MAX(y_new, h - y_new)
create new image (plain or transparent background):
width = new_canter_x * 2
height = new_center_y * 2
copy your old image to new one to coords:
new_center_x - x_new
new_center_y - y_new
imagerotate the new image.
now you just have to cut the part that you are interested in out of it.

Answer 2

The right way to do it is rotate and then crop with right params of transformation.
Another way is move, rotate then move again (simpler math but more code).
$x and $y are coordinates of the red dot.
private function rotateImage($image, $x, $y, $angle)
{
$widthOrig = imagesx($image);
$heightOrig = imagesy($image);
$rotatedImage = $this->createLayer($widthOrig * 2, $heightOrig * 2);
imagecopyresampled($rotatedImage, $image, $widthOrig - $x, $heightOrig - $y, 0, 0, $widthOrig, $heightOrig, $widthOrig, $heightOrig);
$rotatedImage = imagerotate($rotatedImage, $angle, imageColorAllocateAlpha($rotatedImage, 0, 0, 0, 127));
$width = imagesx($rotatedImage);
$height = imagesy($rotatedImage);
$image = $this->createLayer();
imagecopyresampled($image, $rotatedImage, 0, 0, $width / 2 - $x, $height / 2 - $y, $widthOrig, $heightOrig, $widthOrig, $heightOrig);
return $image;
}
private function createLayer($width = 1080, $height = 1080)
{
$image = imagecreatetruecolor($width, $height);
$color = imagecolorallocatealpha($image, 0, 0, 0, 127);
imagefill($image, 0, 0, $color);
return $image;
}