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

[Anton V. Tarasov]

Hi Jim, Sergey and All,

Please review the fix that adds support of Retina displays to 
JLightweightFrame (which javafx SwingNode is based on).

webrev: http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1
jira: https://bugs.openjdk.java.net/browse/JDK-8029455

(After the fix goes into jdk9 it should be ported to 8u20 as well, 
because the functionality is essential for SwingNode.)

The general idea of the fix is as follows.

A BufferedImage instance, being created in the context in which the 
scale factor is determined and is different from one, is automatically 
created with appropriately extended size. The image itself becomes a 
scaled image (a "scale" private field is set on it). By the "context" I 
mean the circumstances where the BufferedImage is related to a  
JLightweightFrame, a GraphicsConfiguration, a SurfaceData, or a 
GraphicsDevice which determine the scale factor.

Here are the related changes:

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/java/awt/image/BufferedImage.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/OffScreenImage.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/swing/JLightweightFrame.java.udiff.html 
(the resizeBuffer method)
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/macosx/classes/sun/lwawt/LWLightweightFramePeer.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/BufferedImageGraphicsConfig.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/macosx/classes/sun/java2d/opengl/CGLGraphicsConfig.java.udiff.html

The "scale" value of a BufferedImage is used when 1) 
BufferedImageGraphicsConfig is created 2) 
BufImgSurfaceData.getDefaultScale() is called:

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/BufferedImageGraphicsConfig.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/BufImgSurfaceData.java.udiff.html

The former is used in the GraphicsConfiguration.createCompatibleImage() 
calls, and the latter is used in SurfaceManager.getImageScale(Image):

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/SurfaceManager.java.udiff.html

A scaled BufferedImage is supported by the SunGraphics2D.drawImage() 
primitives. Here's the pattern of how the image may be created and drawn:

int scale = <get the scale factor from the context>;
BufferedImage img = new BufferedImage(width * scale, height * scale, ...);
img.setScale(scale); // an accessor is currently used instead
<...>
g2d.drawImage(img, x, y, ...); // 1) draw the image with auto-scale
g2d.drawImage(img, x, y, dw, dh, ...) // 2) draw the image into a 
specified rect

In the first case, if the BufferedImage is created with an extended 
size, the "scale" value of the image matters, it should be drawn as a 
HiDPI image.
In the second case, if the BufferedImage is created with an extended 
size, the "scale" value of the image doesn't matter (it may not be 
evidently set) as the image will anyway be scaled from its physical 
bounds into provided logical bounds. This all should (as I suppose) 
provide backward compatibility for buffered images that were created in 
their logical bounds or without setting the "scale" field. For instance, 
the AquaPainter.paintFromSingleCachedImage(...) method creates & draws 
an image as follows:

int scale = ((SunGraphics2D) g).surfaceData.getDefaultScale();
int imgW = bounds.width * scale;
int imgH = bounds.height * scale;
BufferedImage img = new BufferedImage(imgW, imgH, ...);
<paint into the img>
g.drawImage(img, bounds.x, bounds.y, bounds.width, bounds.height, null);

Here, the img.scale value is not set (I didn't modify this code), and 
SunGraphics2D doesn't treat the image as a HiDPI image, however it is 
drawn as expected. An alternative way to draw the image would be:

int scale = ((SunGraphics2D) g).surfaceData.getDefaultScale();
int imgW = bounds.width * scale;
int imgH = bounds.height * scale;
BufferedImage img = new BufferedImage(imgW, imgH, ...);
img.setScale(scale);
<paint into the img>
g.drawImage(img, bounds.x, bounds.y, ...);

The result would be the same.

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/java2d/SunGraphics2D.java.sdiff.html

The following changes:

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/macosx/classes/sun/lwawt/macosx/CPlatformLWView.java.udiff.html

are defined by this logic. Running Swing via JLightweightFrame (JLF) 
makes it "display agnostic". Swing is painted to an off-screen buffer 
and it's the host (e.g. SwingNode) that renders the buffer on a 
particular device. So, the host should detect the scale of the current 
display and set it on JLF.

However, AWT in order to paint to a volatile image requires 
CGraphicsDevice and CGLSurfaceData to be created. By default AWT creates 
CGraphicsDevice instances matching all the detected display devices 
(CGraphicsEnvironment.initDevices()). But, as JLF doesn't have any 
platform window behind it, AWT can't match JLF to the exact device it's 
currently displayed on. So, on the one hand, AWT doesn't know which 
device is current and what is the current scale (the host passes this 
value), but from the other hand, AWT has a list of all the 
CGraphicsDevice instances.

I tried to leverage from that fact. The 
CPlatformLWView.getGraphicsDevice() method takes the current scale from 
the JLF instance, and then tries to match it to an existent device from 
the list. In case it can't find a device with the specified scale (which 
should not actually happen, unless the host passes an arbitrary scale 
value, which is not the case for SwingNode) it takes a default device 
and changes its scale forcedly. I'm not sure if I should create a new 
dummy device instance instead. The scale factor of the device (which is 
then propagated to CGLSurfaceData on its creation) is the only info that 
JLF will take from the device to create a scaled volatile image.

The following changes:

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/javax/swing/JViewport.java.udiff.html
- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/javax/swing/RepaintManager.java.udiff.html

were made to map a backing store image to a scale factor.

The JViewPort.paint(...) method calls SunGraphics2D.copyArea(...) on 
scrolling. The method was not implemented for a graphics with a scale 
transform and a BufImgSurfaceData (it threw exceptions). I took that 
code, copied it to the BufImgSurfaceData.copyArea(...) and added a 
general translation for the coords:

- 
http://cr.openjdk.java.net/~ant/JDK-8029455/webrev.1/src/share/classes/sun/awt/image/BufImgSurfaceData.java.udiff.html

It works, but I'm not sure the implementation is eligible (I don't know 
the details of the Blit class, at least it warns not to use the same 
source and dest).

The rest of the changes (not covered here) should be clear.

Testing:

- Using jfc/SwingSet2 and jfc/Java2D demos (in a standalone mode & 
embedded into SwingNode [1]).
- Testing both Nimbus and Aqua L&F.
- Setting swing.volatileImageBufferEnabled=false/true for all combinations.

Currently, I see no regressions and no visual issues comparing a 
standalone mode and a SwingSet mode.

At the end, I suspect there may be some intersection b/w this fix and 
the fix which introduced MultiResolutionToolkitImage. Unfortunately, I 
didn't yet read that review saga... Please tell me if I should 
incorporate anything from that fix.

Thanks,
Anton.

[1] There's a SwingSet part of the fix which I'm going to post to the 
jfx alias separately.