Bad performance with JOGL and direct buffers

Fri Nov 9 22:23:00 GMT 2007

I recently tried to compile a small JOGL demo with GCJ. I had to use SWT 
because GCJ would throw an exception with AWT and JOGL 1.1 (Exception 
in thread "main" java.lang.IllegalArgumentException: 
GLDrawableFactory.chooseGraphicsConfiguration() was not used when 
creating this Component
 at 
com.sun.opengl.impl.x11.X11GLDrawableFactory.getGLDrawable(jogl.jar.so)) 
- but never mind, the SWT version is faster on Ubuntu Linux anyways.
The GCJ compiled demo runs okay with SWT and JOGL, but the performance 
isn't quite as good as with Sun's JDK 6. The performance is something 
like 128 FPS for GCJ and 200 FPS for JDK 6. When I remove only the 
OpenGL calls from the render loop the performance for both JDK 6 and GCJ 
is equal. It even seems as if all methods except gl.glDrawRangeElements 
do not slow GCJ down. I'm using OpenGL Vertex Buffer Objects with direct 
buffers. The buffers passed to glDrawRangeElements are (many) IntBuffers 
each created like that:
 ByteBuffer bb = ByteBuffer.allocateDirect(byteCount);
 bb.order(ByteOrder.nativeOrder());
 IntBuffer ib = bb.asIntBuffer();
Before starting further investigations: Does anyone have an idea what 
might slow GCJ that much down? I don't think GCJ adds that much of JNI 
overhead (since the empty render loop is equally fast). Are there any 
known GCJ performance problems / pitfalls with direct buffers?
Regards,
Stefan