PHP 5 imagesetpixel参数

Question

I have a quick question regarding PHP's function imagesetpixel. According to the documentation here, the final parameter is a color identifier created with imagecolorallocate. This makes sense. However I found a typo in my program where I was passing hex values directly to imagesetpixel, and it was still working just fine. Is this expected behavior? It's not mentioned in the documentation, so I'm inclined to just stick to using color identifiers, but I figured I'd ask just in case.

Answer 1

Here is what imagecolorallocate() does: https://bitbucket.org/libgd/gd-libgd/src/de7acbfe3e9e43b6b74b740e192915aff4e45a5d/src/gd.c?at=master#cl-518

Basically, it spits out an RGBA value compressed to an int. You can do this because and int has 4 bytes and you need one byte to represent each color.

Now when you pass any value into imagesetpixel() that PHP can convert to an integer, it will work.

You could even do this yourself (not tested, may not work with truecolor contexts):

$im_color = pack('SSSS', $r, $g, $b, $a);

Of course this entire behaviour is subject to change in any future version of GD, which is probably why it's not documented.