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Five More Easy Pieces

Posted by campbell on July 21, 2006 at 1:52 PM PDT

I'm sure you're all sick of reading my blogs at this point, because each time I state definitively that the OpenGL-based Java 2D pipeline is "now better than ever," only to follow it up a couple months later with a blog that says, "no really, this time it's even better," and so on. It reminds me of a nearby store called "Cheaper Then Cheaper Cigarettes" [sic]; can you really improve on "cheaper" like that?

Anyway, at the risk of sounding like the boy who cried wolf, as of Mustang b92, the OGL pipeline is now "better than better", one might even say it's superfantastic. In the spirit of my recent "Five Easy Pieces" entry, here are five more reasons why the OGL pipeline is better than ever...

OGL: scrolling is extremely slow on Nvidia boards

(Bug 6298243)

This bug frustrated me for a number of months, but I was confident that the Nvidia driver engineers would be able to come up with a solution as they've done with so many other issues. Unfortunately, the problem is specific to the way data is laid out in texture memory on certain Nvidia hardware, so a simple driver fix wasn't possible. However, they were kind enough to offer a (somewhat odd) workaround of using the GL_ARB_texture_rectangle extension, since rectangular textures are laid out more efficiently on said hardware and therefore do not exhibit the performance issues reported in this bug.

It took quite a bit of work, but the good news is that we were able to get support for the GL_ARB_texture_rectangle extension implemented for b92, so scrolling/dragging performance is back to normal on Nvidia hardware, for both pbuffers and framebuffer objects (FBOs). As an added bonus, the use of that extension allows us to use less texture memory since we no longer have to pad up to power-of-two sized textures on older hardware. (This is what Michael Scott would call a "win win win" situation.)

OGL: enable sun.java2d.opengl.fbobject by default

(Bug 6439320)

Another big benefit in fixing the previous scrolling performance bug is that it removed the last big barrier that prevented us from enabling the FBO codepath by default. (I mentioned the FBO codepath in a blog entry from last autumn. Note that since then, Ken Russell and I managed to get JOGL's GLJPanel working with the FBO codepath, so that is no longer a barrier.) So as of b92, we've enabled the FBO codepath by default, which has many benefits when compared to the existing pbuffer-based codepath:

  • Reduces costly context-switching overhead. This has helped to improve SwingMark (an internal Swing benchmark) scores by 15-20% on both ATI and Nvidia hardware, when compared to fbobject=false.
  • Greatly improves performance when rendering VolatileImages (especially when applying an AffineTransform).
  • Decreases the amount of VRAM consumed by VolatileImages, due to the fact that we have more control over which buffers are/aren't created.
  • Improves maintainability, since the extension is cross-platform and not tied to any windowing system-isms.
  • Works around a number of pbuffer-specific bugs in ATI's drivers, most notably the one that causes a HotSpot crash when exiting an application.

If you've been been bitten by the OGL pipeline in the past (especially those folks with ATI hardware), I'd highly recommend installing b92 for this change alone.

OGL: use new AffineTransform methods in enableGradientPaint()

(Bug 6434670)

This one's not terribly exciting... Just a three-line change, but I wanted to mention it in case folks are not aware of some new convenience methods added to the AffineTransform class in Mustang. The first is AffineTransform.invert(), which is useful in those cases where you want to invert the transform matrix in place (hence no need to create a new AffineTransform object). The second is AffineTransform.rotate(vecx, vecy), which is helpful when you want to rotate about a vector (instead of using a relative angle value).

In this particular case, the old code was not a major bottleneck in the gradient/texture acceleration path, so there wasn't a huge performance benefit. However, if you have some code that exercises AffineTransform heavily, you might want to check to see if these new methods give you a boost.

OGL: accelerate Gradient/TexturePaint when antialiasing is enabled

(Bug 6436942)

This one is terribly exciting, to me at least. We've had some nifty acceleration for GradientPaint and TexturePaint since the OGL pipeline was introduced in JDK 5, but it always came with the caveat that only non-antialiased primitives were accelerated. But as of Mustang b92, we've figured out a way to use multitexturing to combine the gradient/texture acceleration code with our existing antialiased rendering code, which means GradientPaint and TexturePaint are now fully accelerated by the OGL pipeline, regardless of whether antialiasing is enabled. The bug report has more details, but I'll include the executive summary here, because the numbers speak for themselves:

  • Up to 25x improvement for antialiased TexturePaint operations
  • At least 2-7x improvement for antialiased GradientPaint operations
  • No significant impact on existing accelerated operations

OGL: overlapping LCD glyphs not rendered properly

(Bug 6439274)

This was a visible problem caused by an obscure bug, but fortunately the fix was easy. It was the last known problem with the LCD text acceleration code mentioned in my last blog on the subject, and the driver bugs mentioned there have since been fixed as well.

So if you're a fan of LCD text (meaning everyone but Scott, wink wink) and you have shader level hardware (Nvidia GeForce FX/6/7 series, ATI Radeon 9500 and up, etc), please try -Dsun.java2d.opengl.lcdshader=true and let us know if you see any problems. I'm fairly confident that things are working well, but it hasn't received quite enough testing yet, so we're not planning to enable OpenGL acceleration of LCD text by default in Mustang. Assuming all looks good in the next few months, we can consider turning it on by default in a Mustang update release.

Bonus: The Driver Report

As I've mentioned in past blogs, we've been working with driver teams from Nvidia, ATI, and Sun to ensure that any remaining driver issues are resolved by the time Mustang ships. We have updated our basic acceptance test (BAT) suite with over 50 tests that said driver teams can use to prevent the introduction of new regressions and to test that their existing drivers work well with our OpenGL-based pipeline.

For the past couple years, ATI's drivers have been in a sad state of affairs w.r.t. our OGL pipeline (lots of crashes and rendering artifacts). However, I'm now happy to report that ATI has fixed the remaining Linux-specific OpenGL driver bugs that affect our OGL pipeline, so our BAT suite now runs without failure on their forthcoming 8.27 series release. If you're a Linux user with ATI hardware, I'd suggest upgrading to 8.27 when it becomes available in the next couple weeks.

As for ATI's OpenGL drivers for Windows, some bugs remain and we are continuing to push those with ATI. But as I mentioned above, the change in b92 that makes the FBO codepath the default means that most of those bugs are no longer reproducible for most newer boards.

On the Nvidia and Sun fronts, things are looking really good. There were a couple driver bugs found recently on certain Nvidia laptop GPUs that have since been fixed. If your laptop has an Nvidia GPU and you've been seeing weird artifacts when enabling the OGL pipeline, please install Nvidia's 95.xx series driver when it becomes available in the near future.

In my ears: Viktor Vaughn, "Vaudeville Villain"

In my eyes: Edward P. Jones, "The Known World"

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