<AWT Dev> <Swing Dev> [10] Review request for 8182043: Access to Windows Large Icons

Alexey Ivanov alexey.ivanov at oracle.com
Fri Sep 29 14:11:36 UTC 2017

Hi Sergey and Semyon,

On 28/09/2017 19:49, Sergey Bylokhov wrote:
> On 9/28/17 10:57, Semyon Sadetsky wrote:
>>>> Small and large don't have any special meanings for HiDPI. They are 
>>>> some conditional sizes established by the native platform for the 
>>>> current screen resolution.
>>> The question what is the current screens resolution when you have 
>>> two screens?
>> We should relay on the native platform always. So, the icon size 
>> returned by the native API is the correct approach. And possibility 
>> to use any other sizes is provided as well.
> On windows and Linux we cannot rely on the native system because all 
> HiDPI support is implemented on our(jdk) side, the native system does 
> not know how this icons are used.
>>> It is half of the correct size because on HiDPI it is better to use 
>>> hidpi icons instead of lowdpi. Will the HiDPI unaware apps draw x2 
>>> icons correctly or not depends from our implementation. If we will 
>>> return the MRI then it will be drawn in correct size even if the 
>>> bigger(HiDPI) image will be used.
>> This is not true. MRI has a basic size which uniquely determines its 
>> painted size in component coordinates. The size painted in component 
>> will be the same for all scales this is how HiDPI works in java.
> The size in a component coordinates will be the same, but if HiDPI 
> image is used the real number of pixels to be drawn will be 4 times 
> bigger, because low-dpi images will be scaled x2 and HiDPI images will 
> be drawn as is.
>>>>> For example one of the consumer of this new API is WindowsFileView.
>>>>> How the code below should be changed to work on a different 
>>>>> screens, and request the proper icon?
>>>>> WindowsFileChooserUI.java
>>>>> 1316 icon = getFileChooser().getFileSystemView().getSystemIcon(f);
>>>> Why it should be changed? The code is requesting the proper icon.
>>> Because this method returns an icon of 16x16 pixels, which will be 
>>> rescaled to 32x32 pixels in paint operation.
>> The size should be equal 16x16 otherwise the component view will be 
>> distorted. But painted resolution is determined by native platform. 
>> The native platform may return icon of any size. If the size of the 
>> icon differs from 16x16 (32x32 for example) then it will be wrapped 
>> by MRI of 16x16 size.
> The draw resolution cannot be calculated by the native platform for 
> each window in java. The windows provide a set of icons for each 
> resolution, and we should select correct one depending from the 
> scalefactor of our window. And we should draw bigger icons when the 
> bigger dpi is in use.
> from the example above the code in WindowsFileChooserUI will use 
> low-dpi icons on a HiDPI screen:
> 1316 icon = getFileChooser().getFileSystemView().getSystemIcon(f);
> How we should rewrite this code using a new API to support the icons 
> which are large than default?

If I understand correctly, the introduction of the new API does not 
change the behaviour in this case, does it?

The icon extracted from Windows was 16×16 and will continue to be used.
That is the icon will be scaled when painted.

To support HiDPI displays the implementation of 
|getFileChooser().getFileSystemView().getSystemIcon(f)| should be 
enhanced to fetch the icon at the appropriate size according to the 
current rendering scale. I mean in standard resolution, get 16×16 icon, 
for 125% scale factor, get 20×20 icon, for 150% scale factor, get icon 
24×24. (As far as I know, |IExtractIcon::Extract| does not perform any 
scaling to account for HiDPI rendering. And it really can't because 
different displays can have different DPI settings. Thus if you request 
icon size of 16×16, you'll get 16×16 icon, not 32×32 even if this size 
is more appropriate to the current HiDPI scaling.)

Different icon sizes could be combined into MRI lazily.
To support it, we could use different APIs to extract the icons. For 
example, we can get the list of icon sizes for a file type, and extract 
only “native” size. If larger size is required for HiDPI and the icon 
has it, then get the larger version and use it for rendering rather than 
scaling the one we already have.

However, it looks to be out of the scope for this particular fix. Yet 
this approach will make UI look crispier at higher resolutions.

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