Add get_quality() method for WP_Image_Editor class

[alexvorn2]

We have: (​http://codex.wordpress.org/Class_Reference/WP_Image_Editor)

get_size()
get_output_format()
get_suffix()
get_mime_type()
get_extension()

But no get_quality() function.

[ericlewis]

Is there a use case here, or just accessor parity?

Would adding this to the abstract class WP_Image_Editor (as well as WP_Image_Editor_Imagick and WP_Image_Editor_GD) have any affect on backwards compatibility, in the case a third-party is extending WP_Image_Editor?

[alexvorn2]

Before to resize an image it is important to get the quality of the source image file,

and after that to resize to the same quality.

For example if we have one 40KB image with low quality, why to resize the image to a smaller one with better quality? when we can resize the image to the same quality and the result will be a smaller image with less size. But if we will resize (300x300) 40KB low quality to high quality (250x250), I think the result will have more than 40KB, maybe 400KB.

[markoheijnen]

Add get_quality and merge some of the code from set_quality

[markoheijnen]

We don't know what the original image quality is so your use case will not apply. The bad assumption here would be that the software knows what to do with it.

In the current patch I moved some code around. Reason for this is when we add get_quality() people would be also starting to use set_quality() more. The problem is that when someone uses on of our filters, the filter would always win. Now the default quality value would only be used when no one had set the quality before.

It also abstracts $this->quality away that it's only used in WP_Image_Editor. For now the property stays protected due backwards compatibility. I was thinking about a get() method which sets the value when $this->quality is false.

I will check if we have unit tests for this and add them in case we don't.

[markoheijnen]

Updated unit test.

[wonderboymusic]

In 28879:

Add ->get_quality() method to WP_Image_Editor class.

Adds unit tests.

Props markoheijnen.
Fixes #28154.