Monday, August 6, 2018

Why is JavaFX so slow? SwiftVis2 and Speed Problems with JavaFX 2D Canvas

For the last year or so I've been working on a plotting package called SwiftVis2. There are a number of goals to this project, but a big one is to provide a solid plotting package for Scala that can be used with Spark projects in Scala and which can draw plots with a large number of points. My own personal use case for this is plotting ring simulations often involving millions of particles, each of which is a point in a scatter chart. The figure below shows an example of this made with SwiftVis2 using the Swing/Java2D renderer with 8.9 million particles.

SwiftVis2 plot of ring simulation using Swing renderer.

This particular use case pretty much precludes a lot of browser-based plotting libraries that seem to be popular these days as converting 8.9 million data points to JSON for plotting in JavaScript simply isn't a feasible thing to do for both memory and speed reasons.

As the name SwiftVis2 implies, there is an earlier SwiftVis plotting program. It is a GUI based program written in Java. One of the things that excited me about the upgrade was the ability to use JavaFX instead of Java2D. My understanding is that one of the main reasons for building JavaFX new from the ground up was to take better advantage of graphics cards, and I was really hoping that a JavaFX based rendering engine would outperform one based on the older Java2D library.

I didn't really test this until I was writing up a paper on SwiftVis2 for CSCE'18 and I did performance tests against some other plotting packages. In particular, I compared to Breeze-Viz, which is a Scala wrapper for JFreeChart. JFreeChart uses Swing and Java2D, so I was really hoping that SwiftVis2 would be faster. At the time, I only had a renderer that used JavaFX in SwiftVis2, and I was really disappointed when Breeze-Viz turned out to run roughly twice as fast on a plot like the one above. Tests of NSLP, a different Scala plotting package using Swing/Java2D, showed that it also ran at roughly twice the speed of SwiftVis2 using JavaFX.

Some searching on the internet showed me that there were known issues with drawing too many elements at once on a JavaFX canvas because of the queuing. So I enhanced my renderer to batch the drawing. This has a nice side effect that users can see the plot draw incrementally, so they know their program isn't frozen, but it didn't help the overall speed at all.

Since SwifVis2 was written to allow multiple types of renderers, I went ahead and wrote a Swing renderer that uses Java2D, just to see what the performance was like. The results, shown in the following table, were pretty astounding to me. Note that these times were for drawing plots like the one above. It is also worth noting that upgrading my graphics driver improves the performance for JavaFX more than it did for the Swing based libraries, but even with new drivers, JavaFX is still slower.

PackageRender Time for 8.9 million Points
Breeze-Viz80 secs
SwiftVis2 with JavaFX108 secs
SwiftVis2 with Swing/Java2D13 secs

Keep in mind here that the two SwiftVis2 options are running the exact same code for everything except the final drawing as the only difference is which subclass of my Renderer trait is being used. While I do feel a certain amount of happiness in the fact that SwiftVis2 using Swing is significantly faster than the Breeze-Viz wrapper for JFreeChart, I'm still astounded that JavaFX is nearly 10x slower than Swing/Java2D.

Not only is JavaFX slower, it does an inferior job of antialiasing when drawing circles that are sub-pixel in size. The following figure shows the plot created using the same data and the JavaFX renderer. The higher saturation is obvious. The rendering with Swing/Java2D is the more accurate of the two.

Ring simulation plot made using the JavaFX renderer. Note that the points are sub-pixel and this renderer over-saturates the drawing.
To me, this seems like a serious failing on the part of JavaFX. JavaFX is actually harder to use than Swing, and I always forgave that based on the assumption that special handling was needed to work with the GPU, but that the tradeoff would be significantly improved performance. I can only hope that whatever ails JavaFX in this regard can be fixed and that at some point in the future, JavaFX rendering can match the performance promise that comes with completely rebuilding a GUI/graphics library from the ground up.

Also, in case anyone is wondering why I'm bothering to create yet another plotting package, I will note that SwiftVis2 looks significantly better than JFreeChart, especially in the default behavior. For comparison, the figure below shows the output of the most basic invocation of Breeze-Viz for this plot, which is comparable to the above plots for SwiftVis2. Even if the range on the y-axis is adjusted, it still generally doesn't look as good as the SwiftVis2 output, especially in regards to axis labels. This is the reason I never really got into using JFreeChart in the past. SwiftVis2 is still in the early stages of development, but it already does a better job with my primary use cases.

This is the same figure as those above made with default settings using Breeze-Viz instead of SwiftVis2.
You can find the code for my basic performance tests on GitHub. The data file is not on GitHub because it is rather large. You can find a copy of it on my web space.

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