PHP GD：我可以填充透明部分吗？

Question

There is an image which has transparent area. (png image) Now, while doing a imagecopy, can we just fill that transparent area?

Imagemagick can do this easily. Is that possible in php gd?

Answer 1

A layered approach via imagecopymerge() is one route. The concept is to merge your source image onto a new image, with a pre-set background image, which will show through the source image's transparency once merged.

//create main image - transparent, with opaque red square in middle
$img = imagecreate(60, 60);
$white = imagecolorallocate($img, 255, 255, 255);
imagecolortransparent($img, $white); //make background transparent
$red = imagecolorallocate($img, 255, 0, 0);
imagefilledrectangle($img, imagesx($img) / 4, imagesy($img) / 4, imagesx($img) - (imagesx($img) / 4), imagesy($img) - (imagesy($img) / 4), $red);

//create new image, with pre-filled background, then merge first image across
$img2 = imagecreate(60, 60);
$blue = imagecolorallocate($img2, 0, 0, 255);
imagecopymerge($img2, $img, 0, 0, 0, 0, imagesx($img), imagesy($img), 100);

//output
imagepng($img2);

So the first image creates a transparent image (the white) with a red square in the middle. The second image is simply a blue fill.Merge the two, and the blue shows through the transparent part of the first image, so our red square now sits on the blue fill. Effectively, we've filled the transparent part.

Here's the three states in sequence.