Add imagematch() function

[thg2k]

This function is a replacement for the missing imagecompare() which does not properly check for transparency of truecolor images.

[thg2k]

This would be a replacement for PR #14877

[pierrejoye]

Hi,

Thanks for this (new) PR :)
Before the relevant part, be sure I do not want to refrain your proposal moving forward :) I prefer to ensure we don't add yet another function not covering what it is supposed to do :)

I am not keen to add that one as is, for several reasons:

• it should not be implement in the extension but inside libgd
• it does not do an actual image match, but an pixel values match, which is not what could be expected as it will result in different image formats once saved as well.

I would rather do something like what has been discussed in the other PR, how it is exposed in php can be provided through different functions (bool result for exact match or detailed diff comparison f.e.)

Maybe we can also continue to discuss the implementation details in the other PR as it has all the history and details.

[cmb69]

I prefer to ensure we don't add yet another function not covering what it is supposed to do :)

Good point!

it should not be implement in the extension but inside libgd

I don't necessarily agree. Any complex function should likely be implemented in libgd, but a simple function would not make much sense there (users could easily implement that in C themselves). And such simple functions would only need to be implemented in C for performance reasons (if these are valid, i.e. plain PHP would be considerably slower), in which case implementing them in the libgd bindings might make sense.

[cmb69]

I think we could use gdImageRed() and friends instead. Shouldn't make much of a performance difference.

php-src/ext/gd/libgd/gd.h

Lines 771 to 778 in 6fb79e2

	#define gdImageRed(im, c) ((im)->trueColor ? gdTrueColorGetRed(c) : \
	(im)->red[(c)])
	#define gdImageGreen(im, c) ((im)->trueColor ? gdTrueColorGetGreen(c) : \
	(im)->green[(c)])
	#define gdImageBlue(im, c) ((im)->trueColor ? gdTrueColorGetBlue(c) : \
	(im)->blue[(c)])
	#define gdImageAlpha(im, c) ((im)->trueColor ? gdTrueColorGetAlpha(c) : \
	(im)->alpha[(c)])

[cmb69]

Probably better to use gdImageSX() and gdImageSY().

php-src/ext/gd/libgd/gd.h

Lines 768 to 769 in 6fb79e2

	#define gdImageSX(im) ((im)->sx)
	#define gdImageSY(im) ((im)->sy)

[cmb69]

If we're only interested in a bool return value, we could return here. It might be useful to have an int return, though, which reports how many pixels are different.

[cmb69]

Since there is no PNG involved, this section can be dropped.

[pierrejoye]

See #22532 it adds the perceptual APIs in libgd/
The ext/gd part will be another PR once that one is merged.