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

Jim Graham james.graham at oracle.com
Wed Nov 13 11:28:57 PST 2013

Hi Alexander,

Please read my followup message on the wording for the SunHint 
descriptions.  The version you used in this webrev contains multiple 
conflicting uses of the word "default".

The default value for the hint should be DEFAULT.  Note that Mike has 
already stated that NSImage uses @2x even on non-retina displays so it 
is not clear that the default should be different depending on devScale.

Mike's latest response raises the question - if someone creates an 
application with embedded @2x images, then they will get @2x on Macs 
even if they have a non-retina display (if they use Cocoa).  If we 
follow the same principles here, then a developer developing a Java app 
on a non-retina Mac would see the @2x images when they scale up and 
might get the impression that the @2x images will be used on any display 
with a transform, but the code to deal with them is only in the Mac 
platform code.  Should this support be more universal than that?

The logic for choosing the image scale is incorrect per my previous 
email.  You special case only TRANSLATESCALE which ignores cases where 
the transform was "scaled down to identity" on a retina display (i.e. 
those cases should not default to devScale), and ignores any transform 
with any non-scale components (i.e. g.scale(100,100); g.rotate(.001); 
will use the default resolution even though they scaled it up a lot).

The parameter passed to the getResVariant method is based on the 
subimage size, but the method treats it as if it were based on the full 
image size.  Either compute the scaled size of the full image, or inform 
the method of the sub-image being scaled, or simply pass in the scales, 
otherwise you will get the default image for any sub-image renderings of 
less than half of the original image even if they are rendered at retina 

The code in LWCToolkit.getImage() is not thread safe.  You do lock 
around the cache in the putImage() method, but you could end up 
replacing the image twice with 2 different scalable versions of the 
image since the code in LWCToolkit decided whether to make the image 
outside of any synchronization.

The File/URL code in LWCToolkit is not protected by security permission 
checks like the code in SunToolkit.

The fixes to LWCToolkit require a network connection for every image 
created to see if the @2x version exists.  Originally I thought that 
would be an immense performance hit, but I see that a 
url.openConnection() is done in SunToolkit to verify permissions.  This 
would, however, double the amount of network traffic for every image. 
Also, I'm not sure if url.openConnection() is less overhead than the 
openStream() method used in SunToolkit...?


On 11/13/13 8:11 AM, Alexander Scherbatiy wrote:
>    Could you review the updated fix:
>      http://cr.openjdk.java.net/~alexsch/8011059/webrev.07/
>    -  The default sun hint is added.
>       However, it looks the same as the resolution variant ON hint right
> now. It would better to leave the behavior on the non HiDPI displays the
> same as it was before.
>       So the resolution variant hint is disabled by default for non
> HiDPI displays.
>    - Resolution variant hints description is updated.
>    - The logic operator in the  isHiDPIImage() method is formatted.
>     The @2x images are not preloaded in the LWCToolkit. It really can
> cause image reloading after moving a window from a display from one
> resolution to another.
>     However, it is not clear during the MultiResolutionImage creation
> will the images be used on HiDPI displays or not.
>     May be there should be a flag that enables the high resolution
> images preloading.
>    The original image can be replaced by the high resolution one in the
> paint() method. It causes that the observer could get an image which is
> different from the original one.
>    May be there is no any issue?  If a MultiResolutionImage is not used
> then all works as before. If a user implements MultiResolutionImage may
> be he needs to have an information
>    about the actual drawn image in the observer even it is different
> from the original.
>    Thanks,
>    Alexandr.
> On 11/12/2013 11:43 PM, Jim Graham wrote:
>> Hi Alexander,
>> Some minor issues with this fix:
>> - All RenderingHints have a default setting where the system can
>> choose for you.  The primary thing that the default settings allow is
>> for the answer to be based off of another hint.  Often the QUALITY
>> hint provides the swing vote if an individual hint is left "DEFAULT".
>> That should probably also be the setting used for SG2D, and would
>> hinge off of the devScale, for example, as the deciding factor.
>> - Descriptions for "on" and "off" should be something like "Use
>> resolution variants of images" and "Use only default resolution
>> variants of images" (and "Default resolution variant usage"). Most of
>> the other descriptions on hints are statements of what is going to
>> happen or what is going to be used rather than a simple 'the X state
>> is Y'.
>> - It looks like the transform is used in SG2D to decide if the hiDPI
>> image should be used.  I'm not familiar with the Mac's native use of
>> @2x, but I thought that they hinged the decision off of the "retina
>> scale" of the display, not off of the current transform.  That way, if
>> you scale down an icon it doesn't change its look when it reaches .5x
>> scale (or .75x depending on the cutoff).  Personally, I think it is
>> better to not use the transform to keep animations smooth, but I'm not
>> sure what Apple did.
>> - The logic in using the transform is also a bit murky.  I think if
>> you set the scale on a retina display to exactly 1/2 it would use the
>> HiDPI version even though the scale was 1:1.  Since I support not
>> examining the transform there, I'm going to present this as another
>> reason why we should just base it on devScale, but the logic could be
>> fixed if we really plan to use the transform here.
>> - The new logic in "isHiDPIImage()" is confusing because you line up
>> logic operations from 2 different levels of parentheses.  I believe
>> that one version of our style guidelines included a rule that allowed
>> "indenting to parentheses level" and I would think that would be a
>> good rule to apply here.  Or do something else to make the logic flow
>> there less tricky to read.
>> - Eventually we are going to need this support in more pipelines. I
>> believe that Win8 already has parameters that affect choices of
>> images, but they are only currently deployed on the Surface tablets
>> (i.e. there are no supported high DPI displays for desktop that I'm
>> aware of, but some of the Surface tablets ship with high DPI
>> screens).  What would the impact be if we moved this into a more
>> general class in src/share?  I suppose we might spend extra time
>> looking for variants of images that we don't need?
>> - Has any thought been given to the issues that someone raised with
>> cursors?
>> - Has any thought been given to my comments about MediaTracker and
>> image observer states for multi-res images?  I don't see any attempt
>> here to preload the @2x image.  The problem would probably only be
>> seen on multi-headed systems where one display is retina and one is
>> not - you would find the images suddenly reloading when you move the
>> window to the other screen and the application might not expect that
>> to happen.  Which image is the Observer registered on?  Since the
>> image is handed to the Observer, will an application be surprised when
>> their observer gets a handle to an image they've never seen?  Is it an
>> issue if one of the "alternate resolution variant" images leaks into
>> an application's "hands" via the observer callbacks?
>>             ...jim
>> On 11/11/13 7:59 AM, Alexander Scherbatiy wrote:
>>>   Could you review the updated fix:
>>>      http://cr.openjdk.java.net/~alexsch/8011059/webrev.06/
>>>    Only internal API is exposed:
>>>    - MultiResolutionImage interface with method
>>> "getResolutionVariant(int width, int height)" is added to the
>>> com.sun.awt package
>>>    - Hints to switch on/off the resolution variant usage are added to
>>> SunHints class
>>>    - Test is updated to use the  MultiResolutionImage interface
>>>   Thanks,
>>>   Alexandr.
>>> On 11/5/2013 3:16 PM, Alexander Scherbatiy wrote:
>>>>    Thank you for the review.
>>>>   Could you look at the updated fix:
>>>>      http://cr.openjdk.java.net/~alexsch/8011059/webrev.05/
>>>>   - URL is parsed to protocol, host, port, and path parts in the
>>>> LWCToolkit class.
>>>>      I checked that URL(protocol, host, port, file) constructor
>>>> correctly handles -1 port value.
>>>>   - Only last file name after last '/' in the URL path  is converted
>>>> to @2x name
>>>>   - Tests that check correct URL and path translation to @2x names are
>>>> added to the ScalableImageTest
>>>>   Thanks,
>>>>   Alexandr.
>>>> On 11/1/2013 12:46 AM, Peter Levart wrote:
>>>>> On 10/29/2013 05:45 PM, Alexander Scherbatiy wrote:
>>>>>>> 2. I'm not sure that the proposed getScaledImageName()
>>>>>>> implementation in ScalableToolkitImage works perfectly for URLs
>>>>>>> like this:
>>>>>>> http://www.exampmle.com/dir/image
>>>>>>> In this case it will try to find 2x image here:
>>>>>>> http://www.example@2x.com/dir/image
>>>>>>> which doesn't look correct.
>>>>>>        Fixed. Only path part of a URL is converted to path2x.
>>>>> Hi Alexander,
>>>>> URLs like this:
>>>>> http://www.example.com/dir.ext/image
>>>>> will still be translated to:
>>>>> http://www.example.com/dir@2x.ext/image
>>>>> I think you need to search for last '.' after the last  '/' in the
>>>>> getScaledImageName();
>>>>> Also the following code has some additional bugs:
>>>>>   853         static Image toScalableImage(Image image, URL url) {
>>>>>   854
>>>>>   855             if (url != null && !url.toString().contains("@2x")
>>>>>   856                     && !(image instanceof
>>>>> ScalableToolkitImage)) {
>>>>>   857                 String protocol = url.getProtocol();
>>>>>   858                 String host = url.getHost();
>>>>>   859                 String file = url.getPath();
>>>>>   860                 String file2x =*host +*getScaledImageName(file);
>>>>>   861                 try {
>>>>>   862                     URL url2x = new URL(protocol, host, file2x);
>>>>>   863                     url2x.openStream();
>>>>>   864                     return new ScalableToolkitImage(image,
>>>>> getDefaultToolkit().getImage(url2x));
>>>>>   865                 } catch (Exception ignore) {
>>>>>   866                 }
>>>>>   867             }
>>>>>   868             return image;
>>>>>   869         }
>>>>> Why are you prepending *host* to getScaledImageName(file) in line
>>>>> 860? Let's take the following URL for example:
>>>>> http://www.example.com/dir/image.jpg
>>>>> protocol = "http"
>>>>> host = "www.example.com"
>>>>> file = "/dir/image.jpg"
>>>>> file2x = "*www.example.com*/dir/image at 2x.jpg"
>>>>> url2x =
>>>>> URL("http://www.example.com*www.example.com*/dir/image@2x.jpg")
>>>>> You are missing a part in URL (de)construction - the optional port!
>>>>> For example in the following URL:
>>>>> http://www.example.com:8080/dir/image.jpg
>>>>> You should extract the port from original URL and use it in new URL
>>>>> construction if present (!= -1).
>>>>> I would also close the stream explicitly after probing for existence
>>>>> of resource rather than delegating to GC which might not be promptly
>>>>> and can cause resource exhaustion (think of MAX. # of open file
>>>>> descriptors):
>>>>>         try (InputStream probe = url.openStream()) {}
>>>>> Regards, Peter

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