[OpenJDK 2D-Dev] <AWT Dev> [9] Review Request: JDK-8029455 JLightweightFrame: support scaled painting

[Anton V. Tarasov]

Hi all,

Let me please resume the review process.

With the new webrev:

http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.3

I'm addressing the last concern which was about "leaking" the internal OffscreenHiDPIImage to the 
public via RepaintManager.getOffscreenBuffer.

The explanation will follow, but before that I'd like to share the info related to the volatile 
buffer performance issue (which I was talking about before). I did some investigations of the native 
side and figured out the real source of the performance drop. It's the code where glReadPixels is 
called to read _every_ scanline of the image. This is so because of the nature of the OGL coordinate 
space which is upside down comparing to the j2d space. Please find more details here: 
https://javafx-jira.kenai.com/browse/RT-30035?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=380146. 
If I'm not mistaken, we can do nothing about it.

So, Swing/Interop can't use a volatile image as a back buffer, and it should use a buffered image or 
no back buffer at all. (Otherwise, performance is not acceptable).

Now, to the fix. What I did is I added a "hidpiEnabled" property to the OffscreenHiDPIImage class. 
When it's "true" (by default) the image returns its size in layout space (just like in the previous 
version), when it's "false" the image returns its size in physical space (just like an ordinary 
BufferedImage). In RepaintManager I set the image "hidpi disabled", thus hiding its layout size from 
the developer . The property is taken into account in SunGraphics2D.isHiDPIImage(). Because an 
OffscreenHiDPIImage with hidpiEnabled==false is drawn as an ordinary image, I draw it via 
drawImage(img, x, y, width, height) in RepaintManager.

Why I still use the OffscreenHiDPIImage class instead of a BufferedImage is because otherwise I'd 
have to do pretty the same coding, but it would be scattered. The class basically incapsulates the 
following logic:

- Keeps layout size of the image. (Used in drawImage.)
- Keeps the scale factor. (Used by SurfaceData/VolatileImage/GraphicsConfig.)
- Overrides SurfaceData.getDefaultScale. The point is that I can't simply call Graphics2D.scale(s, 
s) as this won't work when Swing draws into the image. (SunGraphics2D asks SurfaceData for the scale).
- Overrides VolatileImage to make it return a scaled BI as its backup. (Used by Nimbus.)
- Overrides GraphicsConfiguration to let it access the BI and its scale factor. (Used by Nimbus. 
This could be implemented otherwise, but not much better).

No more changes in the current version. I know there're some concerns related to detecting a device 
change, but let me address it after we come to agreement about the approach discussed above.

Thanks,
Anton.


On 18.12.2013 5:03, Jim Graham wrote:
> Hi Anton,
>
> javax.swing.RepaintManager.getOffscreenBuffer is a public method that can now return one of the 
> new HiDPI offscreen images which is a subclass of BufferedImage.  This was what I was worried 
> about in terms of one of these internal double buffers leaking to developer code.  If they test 
> the image using instanceof they will see that it is a BufferdImage and they may try to dig out the 
> raster and get confused...
>
>             ...jim
>
> On 12/17/13 10:21 AM, Anton V. Tarasov wrote:
>> Hi all,
>>
>> Please look at the new version:
>>
>> http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.2
>>
>> It contains the following changes:
>>
>> - All the scale related stuff is moved to the new class:
>> OffScreenHiDPIImage.java
>>
>> - JViewport and RepaintManager no longer cache buffers.
>>
>> - JLightweightFrame has new method: createHiDPIImage(w, h).
>>
>> - JViewport, RepaintManager and AbstractRegionPainter goes the new path
>> to create a HiDPI buffered image.
>>
>> - A new internal property is added: "swing.jlf.hidpiImageEnabled". False
>> by default. It makes JLF.createImage(w, h) forward the call to
>> JLF.createHiDPIImage(w, h). This can be used by a third party code in
>> case it creates a buffered image via Component.createImage(w, h) and
>> uses the image so that it can benefit from being a HiDPI image on a
>> Retina display.
>>
>> For instance, SwingSet2 has an animating Bezier curve demo. Switching
>> the property on makes the curve auto scale smoothly. Please, look at the
>> screenshots:
>>
>> -- http://cr.openjdk.java.net/~ant/JDK-8029455/RoughtCurve.png
>> -- http://cr.openjdk.java.net/~ant/JDK-8029455/SmoothCurve.png
>>
>> - SunGraphics2D now draws a HiDPI buffered image the same way it draws a
>> VolatileImage.
>>
>> - I've removed the copyArea() method from the BufImgSurfaceData, and
>> modified the original version. The only question I have is: do I need to
>> check for "instanceof OffScreenHiDPIImage.SurfaceData" in case when
>> "transformState == TRANSFORM_TRANSLATESCALE"? If this method is invoked
>> with some other SD, and the transform is SCALE, will it do the job with
>> the coordinates conversion done?
>>
>> - I've left the new methods in FramePeer default... May yet we implement
>> them in other peers when we really need it?
>>
>> - CPlatformLWWindow.getGraphicsDevice() checks for an intersection +
>> scale. This heuristic actually may fail when a Window is moved b/w three
>> or four displays so that it intersects them all at some time. JFX will
>> set a new scale factor in between and AWT may pick up a wrong device. I
>> don't know any simple solution for that. For two monitors this will work.
>>
>> Thanks,
>> Anton.