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

[Alexey Ivanov]

Hi Sergey,

On 24/10/2017 00:22, Sergey Bylokhov wrote:
> On 17/10/2017 09:42, Alexey Ivanov wrote:
>>> This is my understanding, before those fix the maximum size was 32x32.
>>
>> It is my understanding too. Thus limiting the size of icon to 128 
>> pixels seemed reasonable.
>>
>> At this moment the buffer for icon pixels is allocated on the stack, 
>> therefore the size cannot be dynamic. If memory for icon pixels is 
>> allocated dynamically, the limitation can be removed.
>>
>> It makes sense to address this limitation under a separate issue, do 
>> you agree?
>
> I agree that this can be moved to a separate bug. But my complaints 
> were not related to it.
>  - The new flags are not strictly specified. It is unclear what are 
> small and large icons. For example the old "getSystemIcon" specified 
> that it returns "an icon as it would be displayed by a native file 
> chooser". How the new flags are related to this? I see that the SMALL 
> flag is the same as the old method, and the large cion is just a HiDPI 
> version of default icon.
>  - SMALL/LARGE flags depends from the native main screen scale, 
> probably it is possible to remove this dependency? Otherwise in the 
> two screen configuration it will produce different images depending 
> from the main screen.

Per my understanding, SMALL and LARGE flags correspond to the previous 
private API behaviour where you could get two icon sizes: 16×16 and 
32×32. These flags will return the same logical-sized icons, subject to 
HiDPI scaling performed by native system.

So these constants provide backward compatibility to 
sun.awt.shell.ShellFolder.getShellFolder(file).getIcon(getLargeIcon): 
either SMALL or LARGE.

>  - In case of multi-monitor config in the discussion above there was a 
> suggestion that the user can create MRI on top of the new API. I am 
> not sure how it will work because we already return MRI for most of 
> the files.
>
> I am still thinking that we should investigate the possibility to 
> return MRI directly w/o ImageIcon/Icon wrappers. This MRI could load 
> data lazily depends from the destination scale. The user ill able to 
> get any resolution variants via getResolutionVariant(double,double) 
> and also can get the list of the icons attached to some file via 
> getResolutionVariants();

My suggestion was to create MRI internally inside the new API. [1] This 
seems like the best option. On the other hand, we need to overcome 
native system scaling, otherwise the rendering could be broken.

Testing performed by you [2] and me [3] shows that native system scales 
the returned hIcon, and, if there are several displays in the system 
with different scaling factors, the underlying icon size could be wrong.

It seems there's no easy-to-use API for icons, Microsoft admits [4] 
working with icons is one of the areas where Win32 API does not provide 
a DPI context. It is still possible to use low-level resource APIs to 
enumerate all the provided sizes in RT_GROUP_ICON resource.


Regards,
Alexey

[1] 
http://mail.openjdk.java.net/pipermail/awt-dev/2017-September/013147.html
[2] http://mail.openjdk.java.net/pipermail/awt-dev/2017-October/013179.html
[3] http://mail.openjdk.java.net/pipermail/awt-dev/2017-October/013181.html
[4] 
https://msdn.microsoft.com/library/windows/desktop/mt843498(v=vs.85).aspx#Common_Pitfalls__Win32__