Initial Mac OS X port of Jogl by Gerard Ziemski and Kenneth Russell,

subsuming the previous prototype implementation (no GLCanvas support) done by Marc Downie. Added user's guide (HTML format) under doc/userguide/index.html. git-svn-id: file:///usr/local/projects/SUN/JOGL/git-svn/svn-server-sync/jogl/trunk@13 232f8b59-042b-4e1e-8c03-345bb8c30851
author: Kenneth Russel <[email protected]> 2003-06-26 13:21:12 +0000
committer: Kenneth Russel <[email protected]> 2003-06-26 13:21:12 +0000
commit: 0a6e191eaebcc8edc2611dbedab6fd04a615fc2f (patch)
tree: 7f8a9b8e88a6bc6662827d3f092b943b1ea893fb /doc/userguide
parent: 2b54833bb15d6cae356fa0c5777d11e152d774cb (diff)
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+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
+<HTML>
+<HEAD>
+<TITLE>Jogl - User's Guide</TITLE>
+</HEAD>
+<BODY>
+
+<H1>Jogl - User's Guide</H1>
+
+<P>
+
+<UL>
+
+  <LI> Overview
+  <LI> Creating a GLDrawable
+  <LI> Writing a GLEventListener
+  <LI> Using the Composable Pipeline
+  <LI> Multithreading Issues
+  <LI> Pbuffers
+  <LI> Platform notes
+  <UL>
+    <LI> All Platforms
+    <LI> Windows
+    <LI> Solaris, Linux (X11 platforms)
+    <LI> Macintosh OS X
+  </UL>
+
+</UL>
+
+<H2> Overview </H2>
+
+<P>
+
+Jogl is a Java programming language binding for the OpenGL 3D graphics
+API. It supports integration with the Java platform's AWT and Swing
+widget sets while providing a minimal and easy-to-use API that handles
+many of the issues associated with building multithreaded OpenGL
+applications. Jogl provides access to the latest OpenGL routines
+(OpenGL 1.4 with vendor extensions) as well as platform-independent
+access to hardware-accelerated offscreen rendering ("pbuffers"). Jogl
+also provides some of the most popular features introduced by other
+Java bindings for OpenGL like GL4Java, LWJGL and Magician, including a
+composable pipeline model which can provide faster debugging for
+Java-based OpenGL applications than the analogous C program.
+
+</P>
+<P>
+
+Jogl was designed for the most recent version of the Java platform and
+for this reason supports only J2SE 1.4 and later. It also only
+supports truecolor (15 bits per pixel and higher) rendering; it does
+not support color-indexed modes. Certain areas of the public APIs are
+more restrictive than in other bindings; for example, the GLCanvas and
+GLJPanel classes are final, unlike in GL4Java, and the GLContext class
+is no longer exposed in the public API. These changes have been made
+to keep the public API simple and because most of the programming
+errors that have been seen with earlier Java/OpenGL interfaces, in
+particular GL4Java, have been related to subclassing the OpenGL widget
+classes and performing manual OpenGL context management. Several
+complex and leading-edge OpenGL demonstrations have been successfully
+ported from C/C++ to Jogl without needing direct access to any of
+these APIs. However, all of these classes and concepts are accessible
+at the Java programming language level in implementation packages, and
+in fact the Jogl binding is itself written almost completely in the
+Java programming language. There are only about fifty lines of
+handwritten C code in the entire Jogl source base; the rest of the
+native code is autogenerated during the build process by a new tool
+called GlueGen, the source code of which is in the Jogl source
+tree. Documentation for GlueGen is forthcoming.
+
+</P>
+
+<H2> Creating a GLDrawable </H2>
+
+<P>
+
+Jogl provides two basic widgets into which OpenGL rendering can be
+performed. The GLCanvas is a heavyweight AWT widget which supports
+hardware acceleration and which is intended to be the primary widget
+used by applications. The GLJPanel is a fully Swing-compatible
+lightweight widget which currently does not support hardware
+acceleration but which is intended to provide 100% correct Swing
+integration in the rare circumstances where a GLCanvas can not be
+used. See <a href =
+"http://java.sun.com/products/jfc/tsc/articles/mixing/">this
+article</a> on <a href = "http://java.sun.com/products/jfc/tsc/">The
+Swing Connection</a> for more information about mixing lightweight and
+heavyweight widgets.
+
+</P>
+<P>
+
+Both the GLCanvas and GLJPanel implement a common interface called
+GLDrawable so applications can switch between them with minimal code
+changes. The GLDrawable interface provides
+
+<UL>
+
+  <LI> access to the GL and GLU objects for calling OpenGL routines
+
+  <LI> the mechanism for registering GLEventListeners for performing
+  OpenGL rendering
+
+  <LI> a <CODE>display()</CODE> method for forcing OpenGL rendering to
+  be performed
+
+  <LI> exclusion methods (<CODE>setRenderingThread()</CODE>,
+  <CODE>setNoAutoRedrawMode()</CODE>) for controlling the
+  multithreading behavior of the widget
+
+  <LI> AWT- and Swing-independent abstractions for getting and setting
+  the size of the widget and adding and removing event listeners
+
+  <LI> a platform-independent mechanism for creating
+  hardware-accelerated offscreen surfaces (pbuffers) for performing
+  advanced rendering techniques
+
+</UL>
+
+</P>
+<P>
+
+GLCanvas and GLJPanel instances are created using the factory methods
+in GLDrawableFactory. These factory methods allow the user to request
+a certain set of OpenGL parameters in the form of a GLCapabilities
+object as well as optionally customize the format selection algorithm
+by specifying a GLCapabilitiesChooser.
+
+</P>
+<P>
+
+A GLCapabilities object specifies the OpenGL parameters for a
+newly-created widget, such as the color, alpha,, z-buffer and
+accumulation buffer bit depths and whether the widget is
+double-buffered. The default capabilities are loosely specified but
+provide for truecolor RGB, a reasonably large depth buffer,
+double-buffered, with no alpha, stencil, or accumulation buffers. 
+
+</P>
+<P>
+
+An application can override the default pixel format selection
+algorithm by providing a GLCapabilitiesChooser to the
+GLDrawableFactory. The chooseCapabilities method will be called with
+all of the available pixel formats as an array of GLCapabilities
+objects; it should return an integer index into this array. The
+DefaultGLCapabilitiesChooser attempts to provide a better
+cross-platform selection algorithm than the WGL and GLX pixel format
+selection algorithms.
+
+</P>
+
+<H2> Writing a GLEventListener </H2>
+
+<P>
+
+Applications implement the GLEventListener interface to perform OpenGL
+drawing. When the methods of the GLEventListener are called, the
+underlying OpenGL context associated with the drawable is already
+current. The listener fetches the GL object out of the GLDrawable and
+begins to perform rendering.
+
+</P>
+<P>
+
+The <CODE>init()</CODE> method is called once, upon context
+creation. (Hooks for context destruction, and support for context
+recreation, are not yet implemented.) The <CODE>display()</CODE>
+method is called to perform per-frame rendering. The
+<CODE>reshape()</CODE> method is called when the drawable has been
+resized; the default implementation automatically resizes the OpenGL
+viewport so often it is not necessary to do any work in this method.
+The <CODE>displayChanged()</CODE> method is designed to allow
+applications to support on-the-fly screen mode switching, but support
+for this is not yet implemented so the body of this method should
+remain empty.
+
+</P>
+<P>
+
+It is strongly recommended that applications always refetch the GL and
+GLU objects out of the GLDrawable upon each call to the
+<CODE>init()</CODE>, <CODE>display()</CODE> and <CODE>reshape()</CODE>
+methods and pass the GL object down on the stack to any drawing
+routines, as opposed to storing the GL in a field and referencing it
+from there. The reason is that multithreading issues inherent to the
+AWT toolkit make it difficult to reason about which threads certain
+operations are occurring on, and if the GL object is stored in a field
+it is unfortunately too easy to accidentally make OpenGL calls from a
+thread that does not have a current context. This will usually cause
+the application to crash. For more information please see the section
+on multithreading.
+
+</P>
+
+<H2> Using the Composable Pipeline </H2>
+
+<P>
+
+Jogl supports the "composable pipeline" paradigm introduced by the
+Magician Java binding for OpenGL. The DebugGL pipeline calls
+<CODE>glGetError</CODE> after each OpenGL call, reporting any errors
+found. It can greatly speed up development time because of its
+fine-grained error checking as opposed to the manual error checking
+usually required in OpenGL programs written in C. The TraceGL prints
+logging information upon each OpenGL call and is helpful when an
+application crash makes it difficult to see where the error occurred.
+
+</P>
+<P>
+
+To use these pipelines, call <CODE>GLDrawable.setGL</CODE> at the
+beginning of the <CODE>init</CODE> method in your GLEventListener. For
+example,
+
+<PRE>
+class MyListener implements GLEventListener {
+  public void init(GLDrawable drawable) {
+    drawable.setGL(new DebugGL(drawable.getGL()));
+    // ...
+  }
+
+  // ...
+}
+</PRE>
+
+</P>
+
+<H2> Multithreading Issues </H2>
+
+<P>
+
+Jogl was designed to interoperate with the AWT, an inherently
+multithreaded GUI toolkit. OpenGL, in contrast, was originally
+designed in single-threaded C programming environments. For this
+reason Jogl provides a framework in which it is possible to write
+correct multithreaded OpenGL applications using the GLEventListener
+paradigm.
+
+</P>
+<P>
+
+If an application written using Jogl interacts in any way with the
+mouse or keyboard, the AWT is processing these events and the
+multithreaded aspects of the program must be considered.
+
+</P>
+<P>
+
+OpenGL applications usually behave in one of two ways: either they
+repaint only on demand, for example when mouse input comes in, or they
+repaint continually, regardless of whether user input is coming in. In
+the repaint-on-demand model, the application can merely call
+<CODE>GLDrawable.display()</CODE> manually at the end of the mouse or
+keyboard listener to cause repainting to be done. Alternatively if the
+application knows the concrete type of the GLDrawable it can call
+repaint() to have the painting scheduled for a later time.
+
+</P>
+<P>
+
+In the continuous repaint model, the application typically has a main
+loop which is calling <CODE>GLDrawable.display()</CODE> repeatedly, or
+is using the Animator class, which does this internally. In both of
+these cases the OpenGL rendering will be done on this thread rather
+than the internal AWT event queue thread which dispatches mouse and
+keyboard events.
+
+</P>
+<P>
+
+Both of these models (repaint-on-demand and repaint continually) still
+require the user to think about which thread keyboard and mouse events
+are coming in on, and which thread is performing the OpenGL rendering.
+OpenGL rendering <B>may not</B> occur directly inside the mouse or
+keyboard handlers, because the OpenGL context for the drawable is not
+current at this point (hence the warning about storing a GL object in
+a field, where it can be fetched and accidentally used by another
+thread). However, a mouse or keyboard listener may invoke
+<CODE>GLDrawable.display()</CODE>.
+
+</P>
+<P>
+
+It is generally recommended that applications perform as little work
+as possible inside their mouse and keyboard handlers to keep the GUI
+responsive. However, since OpenGL commands can not be run from
+directly within the mouse or keyboard event listener, the best
+practice is to store off state when the listener is entered and
+retrieve this state during the next call to
+<CODE>GLEventListener.display()</CODE>.
+
+</P>
+<P>
+
+Furthermore, it is recommended that if there are long computational
+sequences in the GLEventListener's <CODE>display</CODE> method which
+reference variables which may be being simultaneously modified by the
+AWT thread (mouse and keyboard listeners) that copies of these
+variables be made upon entry to <CODE>display</CODE> and these copies
+be referenced throughout display() and the methods it calls. This will
+prevent the values from changing while the OpenGL rendering is being
+performed. Errors of this kind show up in many ways, including certain
+kinds of flickering of the rendered image as certain pieces of objects
+are rendered in one place and other pieces are rendered elsewhere in
+the scene. Restructuring the display() method as described has solved
+all instances of this kind of error that have been seen with Jogl to
+date.
+
+</P>
+<P>
+
+In addition to correctness issues, there are also performance issues
+to consider with multithreaded OpenGL applications. The OpenGL context
+associated with a particular drawable can only be current on one
+thread at a time. If multiple threads may be making the context
+current then this implies that the context must be made current and
+freed during each render; the overhead of these context operations may
+be significant depending on the application. For this reason Jogl has
+a built-in mechanism for optimizing the OpenGL context handling to the
+efficiency of an analogous C application.
+
+</P>
+<P>
+
+<CODE>GLDrawable.setRenderingThread</CODE> informs the Jogl library
+that rendering to a particular drawable will only occur from the
+specified thread. The intent is that the OpenGL context can be made
+current and remain current on that thread until
+setRenderingThread(null) is called. Unfortunately, due to
+quality-of-implementation bugs in the X11 JAWT, this optimization had
+to be made advisory; in other words, it was not possible to guarantee
+that setRenderingThread would yield any faster OpenGL context handling
+on these platforms.
+
+</P>
+<P>
+
+In some situations, typically when an application is using pbuffers to
+compute intermediate results, it is required that automatic redraws be
+suspended for a particular drawable so that the application can
+completely control when and where the display() method is called. For
+this reason the <CODE>GLDrawable.setNoAutoRedrawMode()</CODE> method
+was added; it is used not only by the Jogl implementation but also by
+utility libraries such as gleem (included in the jogl-demos
+distribution). We consider it unfortunate that it was necessary to
+expose two APIs to express basically the same idea and hope that if
+the JAWT implementation in the 1.5 platform has better locking
+behavior that <CODE>GLDrawable.setNoAutoRedrawMode()</CODE> may be
+able to be removed.
+
+</P>
+
+<H2> Pbuffers </H2>
+
+<P>
+
+Jogl exposes hardware-accelerated offscreen rendering (pbuffers) with
+a minimal and platform-agnostic API. Several recent demos have been
+successfully ported from C/C++ to Java using Jogl's pbuffer APIs.
+However, the pbuffer support in Jogl remains one of the more
+experimental aspects of the package and the APIs may need to change in
+the future.
+
+</P>
+<P>
+
+To create a pbuffer, create a GLCanvas and (assuming it reports that
+it can create an offscreen drawable) make a pbuffer using the
+<CODE>createOffscreenDrawable</CODE> API. Because of the multithreaded
+nature of the AWT, the pbuffer is actually created lazily. For this
+reason the application's main loop typically needs to detect when the
+init() methods of all of the GLEventListeners for all of the offscreen
+surfaces have been called. See the demonstrations such as the
+ProceduralTexturePhysics demo for an example of this.
+
+</P>
+<P>
+
+Additionally, pbuffers are only created when the parent GLCanvas's
+display(), init(), or reshape() methods are called; in other words, it
+may be necessary to manually "prime" the GLCanvas by calling display()
+on it until it creates all of its requested pbuffers. Again, please
+see the demonstrations for concrete examples of this. We hope that it
+may be possible to hide many of these details in the future.
+
+</P>
+<P>
+
+A pbuffer is used by calling its display() method. Rendering, as
+always, occurs while the pbuffer's OpenGL context is current. There
+are render-to-texture options that can be specified in the
+GLCapabilities for the pbuffer which can make it easier to operate
+upon the resulting pixels. These APIs are however extremely
+experimental and not yet implemented on all platforms.
+
+</P>
+
+<H2> Platform Notes </H2>
+
+<H3> All Platforms </H3>
+
+<P>
+
+The following issues, among others, are outstanding on all platforms:
+
+</P>
+
+<UL>
+
+<LI> Sharing of textures and display lists between contexts has not
+yet been exposed in the public API, though pbuffers always share
+display lists with their parent widget.
+
+</UL>
+
+<H3> Windows </H3>
+
+<P>
+
+No outstanding issues at this time.
+
+</P>
+
+<H3> Solaris, Linux (X11 platforms) </H3>
+
+<UL>
+
+<LI> Pbuffer support has not yet been implemented in Jogl on X11
+platforms.
+
+</UL>
+
+<H3> Mac OS X </H3>
+
+<P>
+
+The Mac OS X port of Jogl, in particular the GL interface and its
+implementation, can be used either with the provided GLCanvas widget
+or with the Cocoa NSOpenGLView. In order to use it with Cocoa the
+following steps should be taken:
+
+<UL>
+
+<LI> Instantiate a
+<CODE>net.java.games.jogl.impl.macosx.MacOSXGLImpl</CODE> using the
+public constructor taking no arguments.
+
+<LI> Upon the first render of your application, or whenever the
+available OpenGL routines might have changed (because a window moved
+from one screen to another) call the publicly-accessible method 
+<CODE>MacOSXGLImpl.resetGLFunctionAvailability()</CODE>.
+
+<LI> Only use the GL instance when the OpenGL context from the
+NSOpenGLView is current.
+
+</UL>
+
+<B>NOTE:</B> the Cocoa interoperability has not yet been retested
+since the GLCanvas was implemented. Please report any problems found
+with using Jogl with an NSOpenGLView.
+
+</P>
+<P>
+
+The following issues remain with the Mac OS X port:
+
+<UL>
+
+<LI> Due to bugs in the JAWT implementation on Mac OS X, some fairly
+severe workarounds had to be put into the Jogl sources that impact
+performance significantly. These bugs have been fixed by Gerard
+Ziemski at Apple and the fixes will most likely show up in the Java
+that ships with the second developer preview of Panther (10.3), at
+which time the performance of OpenGL-based applications on OS X using
+Jogl and the GLCanvas will increase. Still, with Developer Preview 1
+of Panther (released at JavaOne), resizing of GLCanvases does not work
+and yields an application crash. This issue will be fixed with DP2.
+
+<LI> GLJPanel is not yet implemented on Mac OS X.
+
+<LI> Due to the mechanism by which the Cocoa graphics system selects
+OpenGL pixel formats, the GLCapabilitiesChooser mechanism can not be
+implemented on Mac OS X as on other platforms. In the future, the
+chooser will be used and the capabilities array will contain exactly
+the requested capablities. The underlying Cocoa pixel format selection
+algorithm will then run to choose the best-fit visual. Currently the
+capabilities of the underlying context are hardcoded.
+
+<LI> Pbuffers are not yet supported in the Mac OS X port of Jogl.
+Pbuffers will first become visible to Mac OS X applications in the
+Panther (10.3) release, at which time the pbuffer support will be
+ported.
+
+</UL>
+
+</P>
+
+</BODY>
+</HTML>
author	Kenneth Russel <[email protected]>	2003-06-26 13:21:12 +0000
committer	Kenneth Russel <[email protected]>	2003-06-26 13:21:12 +0000
commit	0a6e191eaebcc8edc2611dbedab6fd04a615fc2f (patch)
tree	7f8a9b8e88a6bc6662827d3f092b943b1ea893fb /doc/userguide
parent	2b54833bb15d6cae356fa0c5777d11e152d774cb (diff)