[OpenJDK 2D-Dev] <AWT Dev> [8] Review request for 8011059 [macosx] Make JDK demos look perfect on retina displays

[Mike Swingler]

On Dec 3, 2013, at 10:10 AM, Jim Graham <james.graham at oracle.com> wrote:

> Hi Mike,
> 
> One more question about @2x handling on MacOS.
> 
> Clearly, in the simple case of someone loading an ordinary "foo.png" and painting it on a retina display without doing anything special with the transform, it will be scaled up by 2x to retain proper size.
> 
> Also, clearly, if a "foo at 2x.png" file exists, it will be loaded automatically and found to be twice as large and displayed with no scaling so that it is the same "size".
> 
> But, what if in the first step they manually specified the image file name as "foo at 2x.png" (and assuming there is no "foo at 2x@2x.png")?  Will it display with its pixels scaled up to double sized because it was the direct image that they specified?

Yes, explicitly asking for "foo at 2x" cause the search machinery to look for "foo at 2x.png" and "foo at 2x@2x.png".

> Or, does the system recognize that it came from a file named @2x and assume that it is a double-screen-resolution image and paint it the same way it would have done if it was implicitly loaded as the higher resolution variant of "foo.png"?

No. Images reps loaded with the @2x suffix are not special — they are just an additional representation of the same named image, and could vary unpredictable in dimensions, bit depth, and color space. We simply prefer that they not. :-)

> Let me spell out the scenarios:
> 
> Scenario 1:
> - app is retina-enabled
> - app has WxH foo.png media (and no @2x versions)
> - app loads image from "foo.png"
> - app displays image with standard default scaling on a retina screen
> => result is image takes up 2W x 2H pixels on the retina screen
> 
> Scenario 2:
> - app is retina-enabled
> - app has WxH foo.png media
> - app also has 2W x 2H foo at 2x.png media
> - app loads image from "foo.png"
> - app displays image with standard default scaling on a retina screen
> => result is system also loads foo at 2x.png and displays it with 2W x 2H retina pixels on the retina screen - the same physical size as in the previous example
> 
> Scenario 3:
> - app is retina-enabled
> - app has WxH foo.png media
> - app also has 2W x 2H foo at 2x.png media
> - app loads image from "foo at 2x.png" rather than "foo.png"
> - app displays image with standard default scaling on a retina screen
> => result is ???
> => I'm guessing that it gets drawn twice the size as Scenario's 1 and 2 because it is no longer relative to the WxH base image?
> 
> Scenario 4:
> same as Scenario 3, but foo.png doesn't exist, foo at 2x.png is the only version found in the media for the app
> => result is ???
> => I'm guessing the result is the same as Scenario 3
> 
> Also, the convention is for the @2x image to be twice the pixel size of the regular image, but what if it isn't?  Is it always drawn at a 0.5x relative scale because of the implication of the @2x file name, or will it be dynamically sized for "basew/@2xw, baseh/@2xh" which just usually works out to 0.5x if the author followed conventions?
> 
> 			...jim

@2x in the file name is just a hack to add more representations to images that are not already multi-rep (.png vs. .tiff and .icns). The actual dimensions of the image dictate when/how it gets used at runtime. I believe the search for @2x variants is only performed if the original image rep is not sufficient to fully fill the rect of pixels in the destination.

Regards,
Mike Swingler
Apple Inc.