File names are generally valid without an extension (although they might be disallowed by upload constraints),
so the filter should deal gracefully with them (“myfile” should return “myfile”, not “myfile.”)
Sometimes a manipulation can’t be carried out, either because the backend isn’t available,
or because there isn’t enough PHP memory available. In these cases, $backend->getImageResource()
will be set to NULL. This should be picked up by manipulateImage(), to avoid passing an invalid
backend into the $callback provided.
The specific case this solves is calling Image->FitMax() on large images:
$resizedImage = $originalImage->FitMax(<width>, <height>)
This will have $resizedImage==$originalImage if the image is smaller than the targeted dimensions,
but with this fix $resizedImage==NULL if the image is too large to be resized.
Which gives custom code the ability to determine which of the two should be used,
for example choosing not to pass the original large image URL to the client
since it wouldn’t be considered a “thumbnail” size.
This has been discussed previously, and was assumed to be handled by PHP automatically:
https://github.com/silverstripe/silverstripe-framework/issues/2739#issuecomment-32603005
It’s unclear if its a regression in SS4.
Tested with PHP 5.6.29, by setting xdebug breakpoints
and inspecting memory_get_usage() before and after GDBackend->manipulateImage().
Even a single 7MB JPEG straight from my DSLR (6000x300) can chomp bring the system from 30MB to >128MB memory use.
That’s in addition to the 7MB of PHP memory required for the $content variable.
Note that the image manipulations likely happen on the raw bitmap, which is much larger than the 7MB compressed JPEG.
Checked ImagickBackend, which doesn’t have this issue (and only uses about half the memory for the same set of images).
