path: root/docs/perf_guide.txt

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		Performance Guide for Java 3D 1.3

I - Introduction

    The Java 3D API was designed with high performance 3D graphics
as a primary goal. This document presents the performance features of 
Java 3D in a number of ways.  It describes the specific APIs that were 
included for performance.  It describes which optimizations are currently 
implemented in Java 3D 1.3.  And, it describes a number of tips and tricks
that application writers can use to improve the performance of their 
application.


II - Performance in the API

    There are a number of things in the API that were included specifically 
to increase performance.  This section examines a few of them.

    - Capability bits
	Capability bits are the applications way of describing its intentions
	to the Java 3D implementation.  The implementation examines the 
	capability bits to determine which objects may change at run time.
	Many optimizations are possible with this feature.

    - isFrequent bits
        Setting the isFrequent bit indicates that the application may frequently 
        access or modify those attributes permitted by the associated capability bit.
        This can be used by Java 3D as a hint to avoid certain optimizations that 
        could cause those accesses or modifications to be expensive. By default the
        isFrequent bit associated with each capability bit is set.

    - Compile
	The are two compile methods in Java 3D.  They are in the 
	BranchGroup and SharedGroup classes.  Once an application calls 
	compile(), only those attributes of objects that have their 
	capability bits set may be modified.  The implementation may then 
	use this information to "compile" the data into a more efficient 
	rendering format.
    
    - Bounds
	Many Java 3D object require a bounds associated with them.  These 
	objects include Lights, Behaviors, Fogs, Clips, Backgrounds, 
	BoundingLeafs, Sounds, Soundscapes, ModelClips, and AlternateAppearance.
	The purpose of these bounds is to limit the spatial scope of the 
	specific object. The implementation may quickly disregard the 
	processing of any objects that are out of the spatial scope of a 
	target object.

    - Unordered Rendering
	All state required to render a specific object in Java 3D is 
	completely defined by the direct path from the root node to the
	given leaf.  That means that leaf nodes have no effect on other
	leaf nodes, and therefore may be rendered in any order.  There 
	are a few ordering requirements for direct descendents of 
	OrderedGroup nodes or Transparent objects.  But, most leaf nodes
	may be reordered to facilitate more efficient rendering.

    - OrderedGroup
        OrderedGroup now supports an indirection table to allow the user to
        specify the order that the children should be rendered. This will
        speed up order update processing, eliminating the expensive 
        attach and detach cycle.   

    - Appearance Bundles
	A Shape3D node has a reference to a Geometry and an Appearance.
	An Appearance NodeComponent is simply a collection of other
	NodeComponent references that describe the rendering characteristics
	of the geometry.  Because the Appearance is nothing but a 
	collection of references, it is much simpler and more efficient for 
	the implementation to check for rendering characteristic changes when
	rendering.  This allows the implementation to minimize state changes 
	in the low level rendering API.

    - NIO buffer support for Geometry by-reference
	NOTE: Use of this feature requires version 1.4 of the JavaTM 2 Platform. 

	This provides a big win in both memory and performance for applications
	that use native C code to generate their geometric data. In many cases, 
	they will no longer need to maintain two copies of their data (one in 
	Java and one in C).  The performance win comes mainly from not having to
	copy the data from their C data structures to the Java array using JNI.
	Also, since the array isn't part of the pool of memory managed by the
	garbage collector, it should speed up garbage collection.


III - Current Optimizations in Java 3D 1.3

    This section describes a number of optimizations that are currently
implemented in Java 3D 1.3. The purpose of this section is to help 
application programmers focus their optimizations on things that will 
compliment the current optimizations in Java 3D.

    - Hardware
	Java 3D uses OpenGL or Direct3D as its low level rendering
	APIs.  It relies on the underlying OpenGL or Direct3D drivers
	for its low level rendering acceleration.  Using a graphics
	display adapter that offers OpenGL or Direct3D acceleration is
	the best way to increase overall rendering performance in Java 3D.

    - Compile
	The following compile optimizations are implemented in the Java 3D
	1.2.1 and 1.3 release:

	    .	Scene graph flattening:  TransformGroup nodes that are
		neither readable nor writable are collapsed into a
		single transform node.

	    .	Combining Shape3D nodes:  Non-writable Shape3D nodes
		that have the same appearance attributes, not pickable,
		not collidable, and are under the same TransformGroup 
		(after flattening) are combined, internally, into a single
		Shape3D node that can be rendered with less overhead.

    - State Sorted Rendering
	Since Java 3D allows for unordered rendering for most leaf
	nodes, the implementation sorts all objects to be rendered on
	a number of rendering characteristics.  The characteristics
	that are sorted on are, in order, Lights, Texture, Geometry
	Type, Material, and finally localToVworld transform.  The only
	2 exceptions are to (a) any child of an OrderedGroup node, and 
	(b) any transparent object with View's Transparency sorting policy
	set to TRANSPARENCY_SORT_GEOMETRY.  There is no state sorting for 
        those objects.

    - View Frustum Culling
	The Java 3D implementation implements view frustum culling.
	The view frustum cull is done when an object is processed for
	a specific Canvas3D.  This cuts down on the number of objects
	needed to be processed by the low level graphics API.

    - Multithreading
	The Java 3D API was designed with multithreaded environments
	in mind.  The current implementation is a fully multithreaded
	system.  At any point in time, there may be parallel threads
	running performing various tasks such as visibility detection,
	rendering, behavior scheduling, sound scheduling, input
	processing, collision detection, and others.  Java 3D is
	careful to limit the number of threads that can run in
	parallel based on the number of CPUs available.

    - Space versus time property
	By default, Java3d only builds display list for by-copy geometry. If
	an application wishes to have display list build for by-ref geometry
	to improve performance at the expense of memory, it can instruct Java3d
	by disable the j3d.optimizeForSpace property to false. For example :
		
		java -Dj3d.optimizeForSpace=false MyProgram
	
	This will cause Java3d to build display list for by-ref geometry and 
	infrequently changing geometry.
	See also : Part II - isFrequent bits, and Part IV - Geometry by reference.
	

IV - Tips and Tricks

    This section presents a number of tips and tricks for an application
programmer to try when optimizing their application.  These tips focus on
improving rendering frame rates, but some may also help overall application
performance.

    - Move Object vs. Move ViewPlatform
	If the application simply needs to transform the entire scene,
	transform the ViewPlatform instead.  This changes the problem
	from transforming every object in the scene into only
	transforming the ViewPlatform.

    - Capability bits
	Only set them when needed.  Many optimizations can be done
	when they are not set.  So, plan out application requirements
	and only set the capability bits that are needed.

    - Bounds and Activation Radius
	Consider the spatial extent of various leaf nodes in the scene
	and assign bounds accordingly.  This allows the implementation
	to prune processing on objects that are not in close
	proximity.  Note, this does not apply to Geometric bounds.
	Automatic bounds calculations for geometric objects is fine.
	In cases such as the influencing or scheduling bounds 
        encompass the entire scene graph, setting this bounds to
	infinite bounds may help improve performance. Java3d will
	shortcircuit intersection test on bounds with infinite
	volume. A BoundingSphere is a infinite bounds if it's radius
        is set to Double.POSITIVE_INFINITY. A BoundingBox is a
        infinite bounds if it's lower(x, y, z) are set to 
	Double.NEGATIVE_INFINITY, and it's upper(x, y, z) are set 
	Double.POSITIVE_INFINITY.
	Bounds computation does consume CPU cycles. If an application
	does a lot of geometry coordinate updates, to improve 
	performance, it is better to turn off auto bounds compute. The
	application will have to do the bounds update itself.
	
    - Change Number of Shape3D Nodes
	In the current implementation there is a certain amount of
	fixed overhead associated with the use of the Shape3D node.
	In general, the fewer Shape3D nodes that an application uses,
	the better.  However, combining Shape3D nodes without
	factoring in the spatial locality of the nodes to be combined
	can adversely effect performance by effectively disabling view
	frustum culling.  An application programmer will need to
	experiment to find the right balance of combining Shape3D
	nodes while leveraging view frustum culling.  The .compile
	optimization that combines shape node will do this
	automatically, when possible.

    - Geometry Type and Format
	Most rendering hardware reaches peak performance when
	rendering long triangle strips.  Unfortunately, most geometry
	data stored in files is organized as independent triangles or
	small triangle fans (polygons).  The Java 3D utility package
	includes a stripifier utility that will try to convert a given
	geometry type into long triangle strips.  Application
	programmers should experiment with the stripifier to see if it
	helps with their specific data.  If not, any stripification
	that the application can do will help.  Another option is that
	most rendering hardware can process a long list of independent
	triangles faster than a long list of single triangle triangle
	fans.  The stripifier in the Java 3D utility package will be
	continually updated to provided better stripification.

    - Sharing Appearance/Texture/Material NodeComponents
	To assist the implementation in efficient state sorting, and
	allow more shape nodes to be combined during compilation,
	applications can help by sharing Appearance/Texture/Material
	NodeComponent objects when possible.

    - Geometry by reference
	Using geometry by reference reduces the memory needed to store
	a scene graph, since Java 3D avoids creating a copy in some
	cases.  However, using this features prevents Java 3D from
	creating display lists (unless the scene graph is compiled),
	so rendering performance can suffer in some cases.  It is
	appropriate if memory is a concern or if the geometry is
	writable and may change frequently.  The interleaved format
	will perform better than the non-interleaved formats, and
	should be used where possible.  In by-reference mode, an
	application should use arrays of native data types; referring
	to TupleXX[] arrays should be avoided.
	See also : Part III - Space versus time property.

    - Texture by reference and Y-up
	Using texture by reference and Y-up format may reduce the
	memory needed to store a texture object, since Java 3D avoids
	creating a copy in some cases.  When a copy of the by-reference 
	data is made in Java3D, users should be aware that this case 
	will use twice as much memory as the by copy case. This is due 
	to the fact that Java3D internally makes a copy in addition to 
	the user's copy to the reference data. Currently, Java3D will not
	make a copy of texture image for the following combinations of
	BufferedImage format and ImageComponent format (byReference
	and Yup should both be set to true):

		On both Solaris and Win32 OpenGL:

	BufferedImage.TYPE_CUSTOM	ImageComponent.FORMAT_RGB8 or
	of form 3BYTE_RGB		ImageComponent.FORMAT_RGB

	BufferedImage.TYPE_CUSTOM	ImageComponent.FORMAT_RGBA8 or
	of form 4BYTE_RGBA		ImageComponent.FORMAT_RGBA

	BufferedImage.TYPE_BYTE_GRAY	ImageComponent.FORMAT_CHANNEL8

		On Win32/OpenGL:

	BufferedImage format		ImageComponentFormat
	----------------------		----------------------
	BufferedImage.TYPE_3BYTE_BGR	ImageComponent.FORMAT_RGB8 or
					ImageComponent.FORMAT_RGB

		On Solaris/OpenGL:

	BufferedImage format		ImageComponentFormat
	----------------------		----------------------
	BufferedImage.TYPE_4BYTE_ABGR	ImageComponent.FORMAT_RGBA8 or
					ImageComponent.FORMAT_RGBA

    - Drawing 2D graphics using J3DGraphics2D
	The J3DGraphics2D class allows you to mix 2D and 3D drawing
	into the same window.  However, this can be very slow in many
	cases because Java 3D needs to buffer up all of the data and
	then composite it into the back buffer of the Canvas3D.  A new
	method, drawAndFlushImage, is provided to accelerate the
	drawing of 2D images into a Canvas3D.  To use this, it is
	recommended that an application create their own BufferedImage
	of the desired size, use Java2D to render into their
	BufferedImage, and then use the new drawAndFlushImage method
	to draw the image into the Canvas3D.

	This has the advantage of only compositing the minimum area
	and, in some cases, can be done without making an extra copy
	of the data.  For the image to not be copied, this method must
	be called within a Canvas3D callback, the specified
	BufferedImage must be of the format
	BufferedImage.TYPE_4BYTE_ABGR, and the GL_ABGR_EXT extension 
	must be supported by OpenGL. If these conditions are not met, 
	the image will be copied, and then flushed. 
		
	The following methods have also been optimized : all drawImage() 
        routines, drawRenderableImage(), draw(Shape s), fill(Shape s), 
	drawString(), drawLine() without strokeSet to copy only the 
	minimum affected region without the restriction imposed in 
	drawAndFlushImage method.

    - Application Threads
	The built in threads support in the Java language is very
	powerful, but can be deadly to performance if it is not
	controlled.  Applications need to be very careful in their
	threads usage.  There are a few things to be careful of when
	using Java threads.  First, try to use them in a demand driven
	fashion.  Only let the thread run when it has a task to do.
	Free running threads can take a lot of cpu cycles from the
	rest of the threads in the system - including Java 3D threads.
	Next, be sure the priority of the threads are appropriate.
	Most Java Virtual Machines will enforce priorities
	aggressively.  Too low a priority will starve the thread and
	too high a priority will starve the rest of the system.  If in
	doubt, use the default thread priority.  Finally, see if the
	application thread really needs to be a thread.  Would the
	task that the thread performs be all right if it only ran once
	per frame?  If so, consider changing the task to a Behavior
	that wakes up each frame.

    - Java 3D Threads
	Java 3D uses many threads in its implementation, so it also
	needs to implement the precautions listed above.  In almost
	all cases, Java 3D manages its threads efficiently.  They are
	demand driven with default priorities.  There are a few cases
	that don't follow these guidelines completely.

	- Behaviors
	    One of these cases is the Behavior scheduler when there
	    are pending WakeupOnElapsedTime criteria.  In this case,
	    it needs to wakeup when the minimum WakeupOnElapsedTime
	    criteria is about to expire.  So, application use of
	    WakeupOnElapsedTime can cause the Behavior scheduler to
	    run more often than might be necessary.

	- Sounds
	    The final special case for Java 3D threads is the Sound
	    subsystem.  Due to some limitations in the current sound
	    rendering engine, enabling sounds cause the sound engine
	    to potentially run at a higher priority than other
	    threads.  This may adversely effect performance.

    - Threads in General
	There is one last comment to make on threads is general.
	Since Java 3D is a fully multithreaded system, applications
	may see significant performance improvements by increasing the
	number of CPUs in the system.  For an application that does
	strictly animation, then two CPUs should be sufficient.  As
	more features are added to the application (Sound, Collision,
	etc.), more CPUs could be utilized.

     - Switch Nodes for Occlusion Culling
       If the application is a first person point of view
       application, and the environment is well known, Switch nodes
       may be used to implement simple occlusion culling.  The
       children of the switch node that are not currently visible may
       be turned off.  If the application has this kind of knowledge,
       this can be a very useful technique.

    - Switch Nodes for Animation
	Most animation is accomplished by changing the transformations
	that effect an object.  If the animation is fairly simple and
	repeatable, the flip-book trick can be used to display the
	animation.  Simply put all the animation frames under one
	switch node and use a SwitchValueInterpolator on the switch
	node.  This increases memory consumption in favor of smooth
	animations.

    - OrderedGroup Nodes
	OrderedGroup and its subclasses are not as high performing as
	the unordered group nodes.  They disable any state sorting
	optimizations that are possible.  If the application can find
	alternative solutions, performance will improve.

    - LOD Behaviors
	For complex scenes, using LOD Behaviors can improve
	performance by reducing geometry needed to render objects that
	don't need high level of detail.  This is another option that
	increases memory consumption for faster render rates.

    - Picking 
	If the application doesn't need the accuracy of geometry based 
	picking, use bounds based picking.  For more accurate picking
	and better picking performance, use PickRay instead of
	PickCone/PickCylnder unless you need to pick line/point.
	PickCanvas with a tolerance of 0 will use PickRay for picking.

    - D3D user only
	Using Quad with Polygon line mode is very slow.  This is because
	DirectX doesn't support Quad.  Breaking down the Quad
	into two triangles causes the the diagonal line to be displayed.
	Instead Java 3D draws the polygon line and does the hidden surface
	removal manually.

	Automatic texture generation mode Eye Linear is slower
	because D3D doesn't support this mode.