With my SN Project slowly coming closer to completion, I decided that I would try out making a simple game to see what needs work, however like always, my plans where derailed quite quickly. I had a small library of images that was working quite well at the time, however after increasing the library to a couple thousand images, I quickly noticed that things where not working quite right, well… actually not at all, it was throwing a java.lang.OutOfMemoryError and crashing. The memory error that as an easy fix, adding a VMOptions tag to the info.plist with -Xmx1024m allowed for me to set the max memory to a much greater amount, however this was nothing more than a temporary fix, I knew there was a much greater issue behind this problem.
The size of the image library was around 150Mb, which when loaded to memory would be larger due to it being uncompressed, however it should not have been much larger than 2X the base size or 300Mb as an upper limit. I was shocked when memory needed skyrocketed to well over 700 Mb, whereas the standard max for the Java VM is around 100Mb. So I went looking for a memory leak. Java handles most memory issues, but it still can have problems with large collections of data gathered in a short period of time, due to the built in garbage collection running only occasionally as needed. After doing some research via Google, I stumbled upon a complaint about the MediaTracker keeping references to the images it tracks, which while in small numbers is not an issue, but can quickly build up as more images are tracked. This was exactly what I was doing wrong.
The standard Image class in java does not load the image into memory right away, instead it acts as a reference until it is needed. This behavior could be seen when removing the method calls to add images to a MediaTracker, the memory used would only increase to around 50Mb and slowly grow as images where loaded when needed. The problem with this is that it causes an issues with flickering in animations. When each frame is used for the first time, it actually draws it on the second call after the first call forces it to be loaded into memory. The standard practice at the time of Java 1.3 to 1.4 was to use a MediaTracker to force the images to load and for my initial use worked quite well. However my project has finally grown beyond the simple use of a MediaTracker. The next step I took was to try some suggestions on limiting the memory retention by removing images from the tracker when they are loaded, or by using separate trackers for each image as well as forcing garbage collection with System.gc(). A mix of these solutions did lower my memory use, however as usual the trade off for space was time and this setup slowed my image loading algorithm to a crawl.
It was quite apparent that I needed something better, and after a bit more research I decided to transition my SN Project from using the base Image class to the improved BufferedImage class available in Java 1.5+. I had actually been using the BufferedImage class for a few things already, but a total transition was not a simple matter. For the most part you can use BufferedImage anywhere you are already using Image, due to the BufferedImage extending the Image class. One huge benefit was that the ImageIO class, instead of the awt Toolkit, loaded the whole image to memory so a MediaTracker is not needed and this sped things up greatly and removed my memory leak. Compared to before, now it only was using around 230Mb, which was well inside my expected limits.
The big problem that I ran into while changing over my code was that the sneaky way I was loading my animation class into my image array on the engine side would no longer be feasible. Originally, I had found a nifty solution to my space problem, with a bit of tweaking my animation class could extend the Image class and then be inserted into my image array for quickly accessing both the game animations and images through one simple method call. It also only needed minimal conditional checks which I already had in place. While this worked well with Image, there is no such luck with BufferedImage. You can serialize a class that extends BufferedImage, but you cannot deserialize it, because as it lacks the "no argument" constructor needed to reconstruct the base class. This left me frustrated and quite annoyed, by this point the editor was ready and working, but the engine would not accept the image data.
A few hours later, I had separated the animations from the image array and while I was sad that I had to abandon my unique solution, it was probably for the best as it is easier to figure out what the code is doing now. This is where big problem two popped up. I was using a PixelGrabber to export my images to an int array and then reconstructing them with MemoryImageSource and the awt Toolkit to load them back into an Image and then forcing them into memory with a MediaTracker. This was not going to work as I was now avoiding the Toolkit and MediaTracker classes. With some more research I finally pieced together that I could do a similar process but this time to a byte array. A simple example of what I am doing is listed below.
Exporting is the same as saving the image, but to a byte stream instead of a file.
ByteArrayOutputStream bstream = new ByteArrayOutputStream(); ImageIO.write(img, "png", bstream); byte bytearray[] = bstream.toByteArray();
To convert the image back you can read the byte array using a ByteArrayInputStream.
BufferedImage image = ImageIO.read(new ByteArrayInputStream(bytearray));
At this point, around ten hours after I started, I now had a working engine and editor again, however it was rendering slower than before. I commented out a most of the drawing and logic method calls and found that the engine would run around 50 FPS with minimal drawing, on the other hand, with all calls back on it ran around 8 FPS. Interestingly enough, the logic was the issue, instead drawing a single large transparent image of the GUI was causing a 40 FPS reduction. I was aware that transparency always causes a speed reduction due to increased processes needed to render it, but not by that much!
It took some more searching to figure out what was wrong. In Java images come in a few different types running in different modes, examples of these would be Image, VolatileImage and BufferedImage. I found VolatileImage quite fascinating as it is the fastest since it is always stored in the graphics hardware memory, but the trade off is that it always may or may not be available due to the possibility of it being overwritten by something else in the limited space of video memory. You must repeatedly check to see if it is still there, the descriptions of this made me think of trying to arrange a large group of very hyper children into a pattern, but at any point they may scatter. Luckily, with new changes in the BufferedImage class it too tries to run in video memory if possible, but only if it is setup to be compatible with the current video configuration. Apparently, using the ImageIO read method does not always create the fastest images, it was suggested that you create a more compatible image using the current graphics configuration and draw the image onto that. This also seems to only cause a minimal increase in processing that is easily outweighed by the huge increase of rendering speed. After converting all the SNEngine's BufferedImage objects with the GraphicsConfiguration createCompatibleImage() method a huge increase could be seen, going from 8FPS to around 35FPS, my target being 30FPS.
I still have some more work to do on increasing efficiency, but this tedious transition was an eye opening experience. As usual I have learned more than I expected, but this new information on Java graphics will probably come in handy later. (NOTE: This was found to be true on OSX 10.6 compiling for Java 1.5+, while most things would be similar on other platforms, the low level hardware acceleration for graphics does slightly differ on each operation system and JDK.)
