PHP/GD, how to copy a circle from one image to another? - php

Question

Is there a reasonably straightforward way to copy a circular area from one image resource to another? Something like imagecopymerge except with circles or ovals etc?
If possible, I want to avoid having to use pre-created image files (any oval shape should be possible), and if there's transparency colours involved they should naturally leave the rest of the image alone.
Reason I'm asking, I have a few classes that allow to apply image operations inside a "selected area" of an image, which works by first deleting that area from a copy of the image, then overlaying the copy back on the original. But what if you want to select a rectangle, and then inside that deselect a circle, and have the operations only affect the area that's left?

Answer 1

You could try this:
Start with original image - $img
Copy that image to a png - $copy
Create a mask png image of the area you want in the circle/ellipse (a 'magicpink' image with a black shape on it, with black set to the colour of alpha transparency) - $mask
Copy $mask over the top of $copy maintaining the Alpha transparency
Change what you need to on $copy
Copy $copy back over $img maintaining the Alpha transparency
// 1. Start with the original image
$img = imagecreatefromjpeg("./original.jpg");
$img_magicpink = imagecolorallocatealpha($img, 255, 0, 255, 127);
//imagecolortransparent($img, $img_magicpink);
// (Get its dimensions for copying)
list($w, $h) = getimagesize("./original.jpg");
// 2. Create the first copy
$copy = imagecreatefromjpeg("./original.jpg");
imagealphablending($copy, true);
$copy_magicpink = imagecolorallocate($copy, 255, 0, 255);
imagecolortransparent($copy, $copy_magicpink);
// 3. Create the mask
$mask = imagecreatetruecolor($w, $h);
imagealphablending($mask, true);
// 3-1. Set the masking colours
$mask_black = imagecolorallocate($mask, 0, 0, 0);
$mask_magicpink = imagecolorallocate($mask, 255, 0, 255);
imagecolortransparent($mask, $mask_black);
imagefill($mask, 0, 0, $mask_magicpink);
// 3-2. Draw the circle for the mask
$circle_x = $w/2;
$circle_y = $h/2;
$circle_w = 150;
$circle_h = 150;
imagefilledellipse($mask, $circle_x, $circle_y, $circle_w, $circle_h, $mask_black);
// 4. Copy the mask over the top of the copied image, and apply the mask as an alpha layer
imagecopymerge($copy, $mask, 0, 0, 0, 0, $w, $h, 100);
// 5. Do what you need to do to the image area
// My example is turning the original image gray and leaving the masked area as colour
$x = imagesx($img);
$y = imagesy($img);
$gray = imagecreatetruecolor($x, $y);
imagecolorallocate($gray, 0, 0, 0);
for ($i = 0; $i > 16) & 0xFF;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;
//for gray mode $r = $g = $b
$color = max(array($r, $g, $b));
$gray_color = imagecolorexact($img, $color, $color, $color);
imagesetpixel($gray, $i, $j, $gray_color);
}
}
// 6. Merge the copy with the origianl - maintaining alpha
imagecopymergegray($gray, $copy, 0, 0, 0, 0, $w, $h, 100);
imagealphablending($gray, true);
imagecolortransparent($gray, $mask_magicpink);
header('Content-Type: image/png');
imagepng($gray);
imagedestroy($gray);