Fixed wrong image resize due to the use of backingScaleFactor instead…

[jaeggerr]

… of using the real image size in pixels

Hi!

If had an issue when trying to downscale images.
For example, an @3x image of 180x180 px gives me:
@2x => 90x90px
@1x => 45x45px

The expected results are
@2x => 120x120px
@1x => 60x60px

The issue is due to the use of NSScreen backingScaleFactor to calculate the real size of the image. I have a screen with a backingScaleFactor of 1.

I corrected the code so that we don't calculate the real image size based on the screen scale factor but by using the real image data.

[terwanerik]

This breaks it on Retina screens, if i drag a 300x300px image (@3x) it generates a 400x400 2x and a 200x200 1x image. I'll try to combine the 2 methods, taking the backingScaleFactor and the image data scale factor. Thanks for the heads up!

[terwanerik]

Could you check it with this code? I only have Retina Macs. #4