12 Java 2D Pipeline Rendering and Properties

This chapter provides information and guidance for troubleshooting some of the most common issues that might be found in the Java 2D API when changing pipeline rendering and properties.

For a summary of Java 2D properties, see Java 2D Properties.

By choosing a different pipeline, or manipulating the properties of a pipeline, you might be able to determine the cause of the problem, and often find a workaround.

In general, you can troubleshoot Java 2D pipeline issues by determining the default pipeline used in your configuration. Then, either change the pipeline to another one, or modify the properties of the default pipeline.

If the problem disappears, then you found a workaround. If the problem persists, then try changing another property or pipeline.

Java 2D uses a set of pipelines, which can be roughly defined as different ways of rendering the primitives. These pipelines are as follows:

• Linux: X11 Pipeline is the default for the Linux operating system.

• Windows OS: DirectDraw/GDI Pipeline is the default on Windows

• Windows OS: Direct3D Pipeline in Full-Screen Mode is an alternative on Windows.

• OpenGL Pipeline in Linux and Windows is an alternative on the Linux operating system, as well as Windows.

Linux: X11 Pipeline

On the Linux operating system, the default pipeline is the X11 pipeline. This pipeline uses the X protocol for rendering to the screen or to certain types of offscreen images, such as VolatileImages, or "compatible" images (images that are created with the GraphicsConfiguration.createCompatibleImage() method).

These types of images can be put into X11 pixmaps for improved performance, especially in the case of the Remote X server.

In addition, in certain cases, Java 2D uses X server extensions, for example, the MIT X shared memory extension, or Direct Graphics Access extension, Double-buffer extension for double-buffering when using the BufferStrategy API.

An additional pipeline, the OpenGL pipeline, might offer greater performance in some configurations.

The following are X11 pipeline properties to troubleshoot.

• X11 Pipeline Pixmaps Properties

• X11 Pipeline MIT Shared Memory Extension

X11 Pipeline Pixmaps Properties

Java 2D by default uses X11 pixmaps for storing or caching certain types of offscreen images.

Only the following types of images can be stored in pixmaps:

• Opaque images, in which case ColorModel.getTransparency() returns Transparency.OPAQUE

• 1-bit transparent images (also known as sprites, Transparency.BITMASK)

The advantage of using pixmaps for storing images is that they can be put into the framebuffer's video memory at the driver's discretion, which improves the speed at which these pixmaps can be copied to the screen or another pixmap.

The use of pixmaps typically results in better performance. However, in certain cases, the opposite is true. These cases typically involve the use of operations that cannot be performed using the X protocol, such as antialiasing, alpha compositing, and transforms that are more complex than simple translation transforms.

For these operations, the X11 pipeline must do the rendering using the built-in software renderer. In most cases, this includes reading the contents of the pixmap to system memory (over the network in the case of remote X server), performing the rendering, and then sending the pixels back to the pixmap. These operations could result in extremely poor performance, especially if the X server is remote.

The following are two cases to disable the use of X11 pipeline:

• Disable X11 pipeline pixmaps:

  To disable the use of pixmaps by Java2D, pass the following property to the Java VM: -Dsun.java2d.pmoffscreen=false.

• Disable X11 pipeline shared memory pixmaps:

  To minimize the effect of operations that require reading pixels from a pixmap on overall performance, the X11 pipeline uses shared memory pixmaps for storing images that are often read from.

  Note:

  The shared memory pixmaps can only be used in the case of a local X server.

  The advantage of using shared memory pixmaps is that the pipeline can get direct access to the pixels in the pipeline, bypassing the X11 protocol, which results in better performance.

  By default, an image is stored in a normal X server pixmap, but it can be later moved to a shared memory pixmap if the pipeline detects excessive reading from such an image. The image can be moved back to a server pixmap if it is copied from often enough.

  The pipeline allows two ways of controlling the use of shared memory pixmaps: either disabling them or forcing all images to be stored in shared memory pixmaps.

  First, try forcing the shared memory pixmaps because it often improves performance. However, with certain video board/driver configurations, it may be necessary to disable the shared memory pixmaps to avoid rendering artifacts or crashes.

  • To disable shared memory pixmaps, set the J2D_PIXMAPS environment variable to server. This is the default in remote X server case.

  • To force all pixmaps to be created in shared memory, set J2D_PIXMAPS to shared.

X11 Pipeline MIT Shared Memory Extension

The Java 2D X11 pipeline uses the MIT Shared Memory Extension (MIT SHM), which allows a faster exchange of data between the client and the X server. This can significantly improve the performance of Java applications.

The following are two ways to improve the performance of the Java application.

• Increase X Server and Java 2D shared memory:

  It is sometimes necessary to increase the amount of shared memory available to the system (and to X server in particular) because the default is too low, resulting in poor rendering performance. Increasing the amount of shared memory and shared memory segments can result in better performance.

  On Linux, this setting can be configured by editing the /proc/sys/kernel/shm* files.

• Disable X11 pipeline shared memory extension:

  In case of problems (such as crashes, or rendering artifacts) with older X servers and the Shared Memory Extension, it is useful to be able to disable the extension. To disable the use of MIT SHM, set the J2D_USE_MITSHM environment variable to false.

Windows OS: DirectDraw/GDI Pipeline

The default pipeline on the Windows platform is a mixture of the DirectDraw pipeline and the GDI pipeline, where some operations are performed with the DirectDraw pipeline and others with the GDI pipeline. DirectDraw and GDI APIs are used for rendering to accelerated offscreen and onscreen surfaces.

The possible issues with the Direct3D pipeline include rendering artifacts, crashes, and performance related problems.

An additional pipeline, the OpenGL pipeline, might offer greater performance in some configurations.

The following are three cases to troubleshoot issues with the Direct3D pipeline such as rendering artifacts, crashes, and performance related problems:

• Disable the DirectDraw pipeline:

  When DirectDraw is disabled, all operations are performed with GDI. Provide the following flag to disable the use of DirectDraw: -Dsun.java2d.noddraw=true. In this case, all offscreen images will be created in the Java heap, and rendered with the default software pipeline. All onscreen rendering, as well as copies of offscreen images to the screen, will be performed using GDI.

• Enable the DirectDraw pipeline:

  If the pipeline was disabled by default for some reason, then it can be enabled by providing the -Dsun.java2d.noddraw=false flag to the VM.

  However, typically there was a reason why it was disabled in the first place, so it is better not to force it.

• Disable the built-in punting mechanism:

  In general, the DirectDraw pipeline attempts to place the offscreen surfaces in the framebuffer's video memory, which provides the fast copies from these surfaces to the screen or other accelerated surfaces, as well as hardware accelerated rendering of certain graphics operations.

  To limit the effect of unaccelerated rendering to VRAM-based surfaces, there exists a punting mechanism, which moves the surface that is detected to be often read from to the system memory. If the surface is found to be copied from often enough, it may be promoted back to video memory.

  However, if the pipeline cannot perform an operation using the DirectDraw API (operations using, for example, alpha compositing, or transforms, or antialiasing), then rendering is performed using the software pipeline. In some cases, this means that the pixels of the destination surface, which resides in VRAM, must be read into system memory, which is a very expensive operation.

  On certain video boards/drivers combinations, the system-memory-based DirectDraw surfaces are known to cause rendering artifacts and other issues. The DirectDraw pipeline provides a way to disable the punting mechanism so that the system memory surfaces are not used.

  To defeat the built-in surface punting mechanism, provide the following flag to the Java VM: -Dsun.java2d.ddforcevram=true.

  Note:

  This mechanism can result in performance degradation because the software loops may be reading pixels from VRAM on each operation. In this case, consider disabling the DirectDraw pipeline.

• Disable the DirectDraw BILT operations:

  In a Bit Block Transfer (BILT) operation, two bitmap patterns are combined. This operation corresponds to a call to the Graphics.drawImage() API.

  In some cases, it is possible to avoid rendering problems by disabling the DirectDraw BLIT operations. GDI BLITs will be used instead.

  Note:

  This operation might result in bad performance. Consider disabling the DirectDraw pipeline instead.

  To disable the use of DirectDraw BLIT operations, pass the parameter -Dsun.java2d.ddblit=false to the Java VM.

Windows OS: Direct3D Pipeline in Full-Screen Mode

This pipeline is enabled in full-screen mode by default, if the drivers support the required features and the level of rendering quality.

It is possible to enable the Direct3D pipeline or to force its use, as described in the following sections.

Consider enabling the Direct3D pipeline for your application if it heavily uses rendering operations such as alpha compositing, antialiasing, and transforms.

However, use caution when deciding to enable this pipeline in your application. For example, some built-in video chipsets (which are used in most notebooks) do not perform well using Direct3D, even if they satisfy the quality requirements for Java 2D pipelines.

The following are three cases to troubleshoot problems with Direct3D API.

1. Disable the Direct3D pipeline:

   Some older video boards/drivers combinations are known to cause issues (both rendering and performance) with the Direct3D pipeline. To disable the pipeline in these cases, pass the parameter -Dsun.java2d.d3d=false to the Java VM, or set the J2D_D3D environment variable to false.

2. Enable the Direct3D pipeline:
   To enable the Direct3D pipeline in both windowed and full-screen mode, use the parameter -Dsun.java2d.d3d=true, or set the J2D_D3D environment variable to true.

   Note:

   The pipeline is enabled only if the drivers support the minimum required features.
3. Diagnose the Direct3D pipeline rendering problems:

   Some rendering issues (like missing pixels, garbled rendering) can be diagnosed by forcing different Direct3D rasterizers. Set the J2D_D3D_RASTERIZER environment variable to one of the following: ref, rgb, hal, or tnl.

   See the Direct3D documentation for a description of these rasterizers. By default, the best rasterizer is chosen based on its advertised capabilities. In particular, the ref rasterizer forces the use of the reference Direct3D rasterizer from Microsoft. If a rendering problem is not reproducible with this rasterizer, then it is likely to be a video driver bug.

   The rgb rasterizer is available only if the Direct3D SDK is installed. The Software Rasterizer for the Microsoft DirectX 9.0 Software Development Kit (SDK) is compatible with Microsoft Direct 3D. This can be obtained from Software Rasterizer for the Microsoft DirectX 9.0 Software Development Kit (SDK). Alternatively, download the Microsoft DirectX® End-User Runtime. For more information about the Direct3D SDK, see Enabling Support for the Direct3D Version 11 DDI.

   For performance or quality problems with text rendering with the Direct3D pipeline, you can force the use of the ARGB texture instead of the default Alpha texture for the Direct3D pipeline's glyph cache. To do this, set the J2D_D3D_NOALPHATEXTURE environment variable to true.

OpenGL Pipeline in Linux and Windows

The OpenGL pipeline is available on Linux and Windows.

This alternate pipeline uses the hardware-accelerated, cross-platform OpenGL API when rendering to VolatileImages, to back buffers created with BufferStrategy API, and to the screen.

This pipeline can offer great performance advantages over the default (X11 or GDI/DirectDraw) pipelines for certain applications. Consider enabling the pipeline for your application if it heavily uses of rendering operations like alpha compositing, antialiasing, and transforms.

The following are use cases for troubleshooting problems in OpenGL pipeline.

• Enable OpenGL Pipeline

• Minimum Requirements

• Diagnose Startup Issues

• Diagnose Rendering and Performance Issues

• Latest OpenGL Drivers

Enable OpenGL Pipeline

The OpenGL pipeline is disabled by default.

To attempt to enable the OpenGL pipeline, provide the following option to the JVM:

-Dsun.java2d.opengl=True

To receive verbose console output about whether the OpenGL pipeline is initialized successfully for a particular screen, set the option to True (note the uppercase T).

Minimum Requirements

The OpenGL pipeline will not be enabled if the hardware or drivers do not meet the minimum requirements.

If one of the following requirements is not met, Java 2D will fall back and use the default pipeline (X11 on Linux or GDI/DirectDraw on Windows), which means your application will continue to work correctly, but without the OpenGL acceleration.

The minimum requirements for the Linux operating system are the following:

• Hardware accelerated OpenGL/GLX libraries installed and configured properly

• OpenGL version 1.2 or higher

• GLX version 1.3 or higher

• At least one TrueColor visual with an available depth buffer

The minimum requirements for Windows OS are the following:

• Hardware accelerated drivers supporting the extensions WGL_ARB_pbuffer, WGL_ARB_render_texture, and WGL_ARB_pixel_format

• OpenGL version 1.2 or higher

• At least one pixel format with an available depth buffer

Diagnose Startup Issues

You can get detailed information about the startup procedures of the OpenGL-based Java 2D pipeline by using the J2D_TRACE_LEVEL environment variable.

As previously mentioned, the OpenGL pipeline might not be enabled on certain machines for various reasons. For example, the drivers might not be properly installed and might report an insufficient version number. Alternatively, your machine might have an older graphics card that does not support the appropriate OpenGL version or extensions.

You can get detailed information about the startup procedures of the OpenGL-based Java 2D pipeline by using the J2D_TRACE_LEVEL environment variable, as shown in the following examples.

Set the J2D_TRACE_LEVEL environment variable on Windows.

# set J2D_TRACE_LEVEL=4
# java -Dsun.java2d.opengl=True YourApp

Set the J2D_TRACE_LEVEL environment variable on Linux.

# export J2D_TRACE_LEVEL=4
# java -Dsun.java2d.opengl=True YourApp

The output will be different depending on your platform and the installed graphics hardware, but it can give you some insight into the reasons why the OpenGL pipeline is not being successfully enabled for your configuration.

Note:

This output is especially useful when filing bug reports intended for the Java 2D team.

Diagnose Rendering and Performance Issues

Because the OpenGL pipeline relies so heavily on the underlying graphics hardware and drivers, it might sometimes be difficult to determine whether rendering or performance issues are being caused by Java 2D or by the OpenGL drivers.

The GL_EXT_framebuffer_object extension provides better performance for rendering and reduced VRAM consumption when using VolatileImages. This "FBO" code path is enabled by default when the OpenGL pipeline is enabled, but only if your graphics hardware and driver support this OpenGL extension. This extension is generally available on Nvidia GeForce/Quadro FX series and later, and on ATI Radeon 9500 and later. If you suspect that the "FBO" code path is causing problems in your application, then you can disable it by setting the following system property:

-Dsun.java2d.opengl.fbobject=false

Setting this property will cause Java 2D to fall back on the older pbuffer-based code path.

If you find that a certain Java 2D operation causes different visual results with the OpenGL pipeline enabled than without, then it probably indicates a graphics driver bug. Similarly, if the performance of Java 2D rendering is significantly worse with the OpenGL pipeline enabled than without, then it is most likely caused by a driver or hardware problem.

In either case, file a detailed bug report through the normal bug reporting channels. See Submit a Bug Report. When filing bug reports, be as detailed as possible, and include the following information:

• Operating system (for example, Ubuntu Linux 6.06, Windows XP SP2)
• Name of graphics hardware manufacturer and device (for example, Nvidia GeForce 2 MX 440)
• Exact driver version (for example, ATI Catalyst 6.8, Nvidia 91.33)
• Output when J2D_TRACE_LEVEL=4 is specified on the command line (as described in the previous section)
• The output of the glxinfo command if you are on Linux

Latest OpenGL Drivers

Because the OpenGL pipeline relies heavily on the OpenGL API and the underlying graphics hardware and drivers, it is very important to ensure that you have the latest graphics drivers installed on your machine. Drivers can be downloaded from your graphics card manufacturer's web site, as shown in the following table.

Manufacturer	Platforms	Cards Known to Work
AMD/ATI	Linux, Windows	Radeon 8500 and later, FireGL series
Nvidia	Linux, Windows	GeForce 2 series and later, Quadro FX series and later
Xi Graphics	Linux	Various (check with Xi Graphics)