eScience Lectures Notes : Transformations in Java3D

Slide 1 : Grouping Shapes and Transforming Group

Grouping Shapes and Transforming Group

Introduction : Grouping shape

BranchGroup Class Methods and example

Switch Class Methods and Examples

Sharing Groups of Shapes : SharedGroup Node

Introduction : Transforming Shapes

Transform3D Class Methods : Helpers

Transform3D Class Methods : Helpers (2)

Transforming Vectors and Points

TransformGroup Example Code

Slide 2 : Grouping Shapes and Transforming Group

Grouping Shapes and Transforming Group

Grouping Shapes

We want to be able to "clump" elements of the scene in certain ways
There are several different types of groups, depending on what properties you want the clumped elements to have
Each group can have any number of children
With one exception, Java 3D reserves the right to render the children in any order

Exemple : ExSwitch

Slide 3 : Types of Groups

Types of Groups

Java 3D provides several types of groups:

Group
BranchGroup
OrderedGroup
DecalGroup
SharedGroup
Switch
TransformGroup

All groups manage a list of children nodes

Shapes, lights, sounds, behaviors

Slide 4 : Group Class Hierarchy

Group Class Hierarchy

All groups share attributes inherited from the Group class

Class Hierarchy

java.lang.Object
	javax.media.j3d.SceneGraphObject
		javax.media.j3d.Node
			javax.media.j3d.Group
				javax.media.j3d.BranchGroup
				javax.media.j3d.OrderedGroup
					javax.media.j3d.DecalGroup
				javax.media.j3d.SharedGroup
				javax.media.j3d.Switch
				javax.media.j3d.TransformGroup

Slide 5 : Groups

Groups

The Group class is the most general-purpose of the group nodes
- Has exactly one parent
- Can have any number of children
You can add, insert, remove, and get children in a group
- Children are implicitly numbered starting with 0
- Child rendering order is up to Java 3D!
Java 3D can sort shapes for better rendering efficiency

The Group node object is a general-purpose grouping node. Group nodes have exactly one parent and an arbitrary number of children that are rendered in an unspecified order (or in parallel). Null children are allowed; no operation is performed on a null child node. Operations on Group node objects include adding, removing, and enumerating the children of the Group node. The subclasses of Group node add additional semantics.

Slide 6 : Group Class Methods

Group Class Methods

Method	Default
Group( )	-
void addChild( Node child ) Appends the specified child to this node's list of children.	None
void setChild( Node child, int index ) Replaces the node's specified child with the child provided.	None
void insertChild( Node child, int index ) Inserts the node's specified child at the specified index location.	None
getChild(int index) Returns the node's index selected child.	None
void removeChild( int index ) Removes the node's child at the specified index location.	None

Slide 7 : BranchGroups

BranchGroups

A BranchGroup is a major sub-tree of the scene graph
- Can be attached to a Locale
- Can be compiled as a unit
- Can be included as a child of a group node in another subgraph
- Can be reparented or removed at runtime
Adding a BranchGroup to a Locale makes the group live
- Once live, changes are constrained to those enabled by capabilities
BranchGroup extends the Group class
DecalGroup adds no additional methods beyond those of the OrderedGroup class

The BranchGroup serves as a pointer to the root of a scene graph branch; BranchGroup objects are the only objects that can be inserted into a Locale's set of objects. A subgraph, rooted by a BranchGroup node can be thought of as a compile unit.

The following things may be done with BranchGroup:

A BranchGroup may be compiled by calling its compile method. This causes the entire subgraph to be compiled. If any BranchGroup nodes are contained within the subgraph, they are compiled as well (along with their descendants).
A BranchGroup may be inserted into a virtual universe by attaching it to a Locale. The entire subgraph is then said to be live.
A BranchGroup that is contained within another subgraph may be reparented or detached at run time if the appropriate capabilities are set.

Note that that if a BranchGroup is included in another subgraph, as a child of some other group node, it may not be attached to a Locale.

Slide 8 : BranchGroup Class Methods

BranchGroup Class Methods

BranchGroup Class Methods	Default
BranchGroup( )	-
void compile( )	None
void detach( )	None

   Locale locale = new Locale( universe );
   Shape3D shape = new Shape3D( geom, app );
   . . .
   BranchGroup branch = new BranchGroup( );
   branch.addChild( shape );
   branch.compile( );
   . . .
   locale.addBranchGraph( branch );

Slide 9 : OrderedGroups

OrderedGroups

An OrderedGroup guarantees children are rendered in first-to-last order
Unlike Group, BranchGroup, etc.
Good for avoiding Z-fighting artifacts
OrderedGroup extends the Group class
OrderedGroup adds no additional methods beyond those of the Group class
BranchGroup extends the OrderedGroup class

The OrderedGroup node guarantees that Java 3D will render its children in their index order. Only the OrderedGroup node and its subclasses make any use of the order of their children during rendering.

Slide 10 : DecalGroups

DecalGroups

DecalGroup extends OrderedGroup and renders children in order
- Children must be co-planar
- First child is the underlying surface
- The underlying surface must encompass all other children
- Use for rendering decal geometry
  - Text
  - Texture Decals (eg, insignia on an airplane wing)
DecalGroup adds no additional methods beyond those of the OrderedGroup class

   Shape3D encompass = new Shape3D( geom, app );
   Shape3D decal1 = new Shape3D( geom1, app1 );
   Shape3D decal2 = new Shape3D( geom2, app2 );
   . . .
   DecalGroup decals = new DecalGroup( );
   decals.addChild( encompass );
   decals.addChild( decal1 );
   decals.addChild( decal2 );

The DecalGroup node is a subclass of the OrderedGroup node. The DecalGroup node is an ordered group node used for defining decal geometry on top of other geometry. The DecalGroup node specifies that its children should be rendered in index order and that they generate coplanar objects. Examples include painted decals or text on surfaces and a checkerboard layered on top of a table.

The first child, at index 0, defines the surface on top of which all other children are rendered. The geometry of this child must encompass all other children; otherwise, incorrect rendering may result. The polygons contained within each of the children must be facing the same way. If the polygons defined by the first child are front facing, then all other surfaces should be front facing. In this case, the polygons are rendered in order. The renderer can use knowledge of the coplanar nature of the surfaces to avoid Z-buffer collisions. (If, for example, the underlying implementation supports stenciling or polygon offset, then these techniques may be employed.) If the main surface is back facing, then all other surfaces should be back facing and need not be rendered (even if back-face culling is disabled).

Note that using the DecalGroup node does not guarantee that Z-buffer collisions are avoided. An implementation of Java 3D may fall back to treating DecalGroup node as an ordinary OrderedGroup node.

Slide 11 : Switches

Switches

A Switch selects zero, one, or multiple children to render
Which child to render can be an integer child number, or bits in a mask
Similar to a Java "switch" statement
This node is only a switch, it does not imply any rendering order
Switch extends the Group class

The Switch group node allows a Java 3D application to choose dynamically among a number of subgraphs. The Switch node contains an ordered list of children and a switch value. The switch value determines which child or children Java 3D will render. Note that the index order of children is used only for selecting the appropriate child or children-it does not specify rendering order.

Slide 12 : Selecting Children

Selecting Children

Select which child to render by its child index
Special values:
- Render no children: CHILD_NONE
- Render all children: CHILD_ALL
Or select a set of children with a bit mask
- A value of CHILD_MASK enables mask use
- Set a member of a Java BitSet for each child to render

These values, when used in place of a nonnegative integer index value, indicate which children of the Switch node are selected for rendering. A value of CHILD_NONE indicates that no children are rendered. A value of CHILD_ALL indicates that all children are rendered, effectively making this Switch node operate as an ordinary Group node. A value of CHILD_MASK indicates that the childMask BitSet is used to select the children that are rendered.

public class BitSet
extends Object
implements Cloneable, Serializable
This class implements a vector of bits that grows as needed. Each component of the bit set has a boolean value. The bits of a BitSet are indexed by nonnegative integers. Individual indexed bits can be examined, set, or cleared. One BitSet may be used to modify the contents of another BitSet through logical AND, logical inclusive OR, and logical exclusive OR operations.
By default, all bits in the set initially have the value false.

Slide 13 : Switch Class Methods and Examples

Switch Class Methods and Examples

Method	Default
Switch( )	-
void setWhichChild( int index )	CHILD_NONE
void setChildMask( BitSet mask )	None

 
   Shape3D first = new Shape3D( geom1, app1 );
   Shape3D second = new Shape3D( geom2, app2 );
   Shape3D third = new Shape3D( geom3, app3 );
   . . .
   Switch group = new Switch( );
   group.addChild( first );
   group.addChild( second );
   group.addChild( third );
   . . .

   setWhichChild(1);

Slide 14 : Sharing Groups of Shapes : SharedGroup Node

Sharing Groups of Shapes : SharedGroup Node

Some shapes occur over and over in a scene
- Marble columns in a colonnade
- Basic user interface components
Sharing enables you to create one master definition of a shape then link to it multiple times in the scene
A SharedGroup extends Group
- It contains shapes, like other groups
- It is never added into the scene graph directly
- It is referenced by one or more Link nodes
Changes to a SharedGroup affect all references to it
Can be compiled by calling its compile( ) method prior to referencing it from a Link node
Link extends the Leaf class

Slide 15 : SharedGroup Class Methods

SharedGroup and Link Class Methods

Method	Default
SharedGroup( )	-
void compile( )	None

Method	Default
Link( )	-
Link( SharedGroup group )	-
void setSharedGroup( SharedGroup group )	None

Slide 16 : SharedGroup Example Code

SharedGroup Example Code

   TransformGroup groupA = new TransformGroup( );
   TransformGroup groupB = new TransformGroup( );
   Shape3D shape1 = new Shape3D( geom1, app1 );
   Shape3D shape2 = new Shape3D( geom2, app1 );
   . . .
   SharedGroup shared = new SharedGroup( );
   shared.addChild( shape1 );
   shared.addChild( shape2 );
   shared.compile( );
   . . .
   Link linkA = new Link( shared );
   Link linkB = new Link( shared );
   . . .
   groupA.addChild( linkA );
   groupB.addChild( linkB );

Slide 17 : Transforming Shapes

Transforming Shapes

By default, all shapes are built within a world coordinate system
Right-handed (X right, Y up, Z toward viewer)

Slide 18 : TransformGroup

TransformGroup

A TransformGroup enables you to build a new coordinate system relative to a parent
- Translate
- Rotate
- Scale
Shapes built in the new coordinate system are relative to it
If you translate the coordinate system, the shapes move too
Transformations accumulate as the scene graph is traversed
- This creates an overall Composite Modeling Transform (CMT)
Transformations lower (closest to the geometry) in the scene graph appear to happen before those farther up in the scene graph
TransformGroup extends the Group class

The TransformGroup node specifies a single spatial transformation-via a Transform3D object -that can position, orient, and scale all of its children.
The specified transformation must be affine. Further, if the TransformGroup node is used as an ancestor of a ViewPlatform node in the scene graph, then the transformation must be congruent-only rotations, translations, and uniform scales are allowed in a direct path from a Locale to a ViewPlatform node. A BadTransformException is thrown if an attempt is made to specify an illegal transform.
------------------------------------------------------------------------
Note: Even though arbitrary affine transformations are allowed, better performance will result if all matrices within a branch graph are congruent-containing only rotations, translation, and uniform scale.
------------------------------------------------------------------------
The effects of transformations in the scene graph are cumulative. The concatenation of the transformations of each TransformGroup in a direct path from the Locale to a Leaf node defines a composite model transformation (CMT) that takes points in that Leaf node's local coordinates and transforms them into Virtual World (Vworld) coordinates. This composite transformation is used to transform points, normals, and distances into Vworld coordinates. Points are transformed by the CMT. Normals are transformed by the inverse-transpose of the CMT. Distances are transformed by the scale of the CMT. In the case of a transformation containing a nonuniform scale or shear, the maximum scale value in any direction is used. This ensures, for example, that a transformed bounding sphere, which is specified as a point and a radius, continues to enclose all objects that are also transformed using a nonuniform scale.

Slide 19 : TransformGroup Class Methods

TransformGroup Class Methods

Method	Default/possible values
public TransformGroup( )	Identity
public TransformGroup(Transform3D t1)
public void setTransform( Transform3D xform )	Identity
public void getTransform(Transform3D t1)
public final void setCapability(int bit) (from SceneGraphObject)	ALLOW_TRANSFORM_READ / ALLOW_TRANSFORM_WRITE
public final boolean getCapability(int bit) (from SceneGraphObject)

Slide 20 : Transform3D

Transform3D

A Transform3D describes the transform used by a TransformGroup
- Represented as a 4x4 double precision matrix
- Can represent translation, rotation, scaling, and shear
- Must be affine (ie, no perspective-like homogeneous division)
Transforms must be congruent if used in a TransformGroup that is an ancestor of a ViewPlatform (ie, no non-uniform scaling)

Just stay with simple combination and you won't have any trouble

Transform3D extends the Object class

shear [n.]

(§ Homonym: sheer)
1. A machine that cuts sheet metal by passing a blade through it.
2. (Physics) A deformation of an object in which parallel planes remain parallel but are shifted in a direction parallel to themselves; "the shear changed the quadrilateral into a parallelogram."

Slide 21 : 4x4 Matrix Transforms

4x4 Matrix Transforms

x'
y'
z'
w'

A B C D
E F G H
I J K L
M N O P

 x
 y
 z
 w

Translation is encoded in D, H, L
Scaling and rotation are encoded in A, B, C, E, F, G, I, J, K
Usually , [M N O P] = [0 0 0 1]

Slide 22 : Internal Matrix Types

Internal Matrix Types

Java 3D keeps track internally of what type of matrix this is
This enables Java 3D to perform operations more efficiently
- AFFINE
- CONGRUENT
- IDENTITY
- NEGATIVE_DETERMINANT
- ORTHOGONAL
- RIGID
- SCALE
- TRANSLATION
- ZERO
getType()
Returns the type of this matrix as an or'ed bitmask of of all of the type classifications to which it belongs.

A generalized transform object represented internally as a 4x4 double-precision floating point matrix. The mathematical representation is row major, as in traditional matrix mathematics. A Transform3D is used to perform translations, rotations, and scaling and shear effects.
A transform has an associated type, and all type classification is left to the Transform3D object. A transform will typically have multiple types, unless it is a general, unclassifiable matrix, in which case it won't be assigned a type.
The Transform3D type is internally computed when the transform object is constructed and updated any time it is modified. A matrix will typically have multiple types. For example, the type associated with an identity matrix is the result of ORing all of the types, except for ZERO and NEGATIVE_DETERMINANT, together. There are public methods available to get the ORed type of the transformation, the sign of the determinant, and the least general matrix type. The matrix type flags are defined as follows:* ZERO - zero matrix. All of the elements in the matrix have the value 0.
* IDENTITY - identity matrix. A matrix with ones on its main diagonal and zeros every where else.
* SCALE - the matrix is a uniform scale matrix - there are no rotational or translation components.
* ORTHOGONAL - the four row vectors that make up an orthogonal matrix form a basis, meaning that they are mutually orthogonal. The scale is unity and there are no translation components.
* RIGID - the upper 3 X 3 of the matrix is orthogonal, and there is a translation component-the scale is unity.
* CONGRUENT - this is an angle- and length-preserving matrix, meaning that it can translate, rotate, and reflect about an axis, and scale by an amount that is uniform in all directions. These operations preserve the distance between any two points, and the angle between any two intersecting lines.
* AFFINE - an affine matrix can translate, rotate, reflect, scale anisotropically, and shear. Lines remain straight, and parallel lines remain parallel, but the angle between intersecting lines can change.A matrix is also classified by the sign of its determinant:NEGATIVE_DETERMINANT - this matrix has a negative determinant. An orthogonal matrix with a positive determinant is a rotation matrix. An orthogonal matrix with a negative determinant is a reflection and rotation matrix.The Java 3D model for 4 X 4 transformations is:

   [ m00 m01 m02 m03 ] [ x ] [ x' ]
   [ m10 m11 m12 m13 ] . [ y ] = [ y' ]
   [ m20 m21 m22 m23 ] [ z ] [ z' ]
   [ m30 m31 m32 m33 ] [ w ] [ w' ]
   
   x' = m00 . x+m01 . y+m02 . z+m03 . w
   y' = m10 . x+m11 . y+m12 . z+m13 . w
   z' = m20 . x+m21 . y+m22 . z+m23 . w
   w' = m30 . x+m31 . y+m32 . z+m33 . w

Note: When transforming a Point3f or a Point3d, the input w is set to 1. When transforming a Vector3f or Vector3d, the input w is set to 0.

Slide 23 : Transform3D Class Methods

Transform3D Class Methods

Method
Transform3D( ) (Default : Identity)
Transform3D( Matrix4d mat )
Transform3D( Matrix3d rot, Vector3d trans, double scale )
Transform3D(..... see the doc API )

void set( Matrix4d mat )
void set( Matrix3d rot, Vector3d trans, double scale )

public final void get(Matrix4d matrix) ..... VOID !

public final void mul(Transform3D t1) ..... this = this * t1
public final void mul(Transform3D t1, Transform3D t2) ..... this = t1*t2

Slide 24 : Building Transforms

Building Transforms

Transforms may be built by:
- Creating matricies by hand
- Using helper methods to build Matrix4d objects
- Using helper methods to build Transform3D objects
Helper methods can:
- Set the transform to identity
- Set the translation
- Set the rotation for X, Y, and Z axes
- Set the scale (uniform and non-uniform)

Slide 25 : Transform3D Class Methods : Helpers

Transform3D Class Methods : Helpers

Setting the transform to identity	void setIdentity( )
Setting the transform to a translation	void set( Vector3d trans )

Setting the transform to a rotation	void rotX( double angle )
	... rotY, rotZ
only about angle passing through the origin	void set( AxisAngle4d axang )
	set( Matrix3d rot )

Setting the transform to a scale factor (uniform or XYZ)	void set( double scale )
	void setScale( Vector3d scale )

Method

Slide 26 : Transform3D Class Methods : Helpers (2)

Transform3D Class Methods : Helpers (2)

Modifying parts of an existing transform
Leaves rest of transform unaffected Method

void setTranslation( Vector3d trans )

void setRotation( AxisAngle4d axang )

void setRotation( Matrix3d rot )

void setEuler( Vector3d rollPitchYaw )

void setScale( double scale )

lookAt

public void lookAt(Point3d eye, Point3d center, Vector3d up)

Helping function that specifies the position and orientation of a view matrix. The inverse of this transform can be used to control the ViewPlatform object within the scene graph.
Parameters:
eye - the location of the eye
center - a point in the virtual world where the eye is looking
up - an up vector specifying the frustum's up direction

AxisAngle4f(float x, float y, float z, float angle)

Constructs and initializes a AxisAngle4f from the specified xyzw coordinates.

AxisAngle4f(Vector3f axis, float angle)

Constructs and initializes an AxisAngle4f from the specified axis and angle.

Slide 27 : Transforming Vectors and Points

Transforming Vectors and Points

During rendering, Java 3D processes geometry coordinates and vectors through each Transform3D
You can use Transform3D helper methods to do this processing on your own points and vectors
- For Point3d, "w" is set to 1
- For Vector3d, "w" is set to 0

Method
void transform( Point3d inout )
void transform( Point3d in, Point3d out )
void transform( Vector3d inout )
void transform( Vector3d in, Vector3d out )

Slide 28 : TransformGroup Example Code

TransformGroup Example Code

Shape3D shape = new Shape3D( geom, app );
. . .
Transform3D transLeft = new Transform3D( );
transLeft.set( new Vector3d( -1.0, 0.0, 0.0 ) );
. . .
TransformGroup group = new TransformGroup( );
group.setTransform( transLeft );
group.addChild( shape );

rotateAngle = Math.PI/10.0;
rotateXPlus = new Transform3D();
rotateXPlus.rotX(rotateAngle);

tmpT = new Transform3D(rotateXPlus);
viewTransform.mul(tmp, viewTransform)
System.out.println("Rotation Plus X ");
System.out.println(viewTransform);
viewTransformGroup.setTransform(viewTransform);

eScience Lectures Notes : Transformations in Java3D

Grouping Shapes and Transforming Group

Introduction : Grouping shape

Introduction : Transforming Shapes

Grouping Shapes and Transforming Group

Grouping Shapes

We want to be able to "clump" elements of the scene in certain ways

There are several different types of groups, depending on what properties you want the clumped elements to have

Each group can have any number of children

With one exception, Java 3D reserves the right to render the children in any order

Exemple : ExSwitch

Types of Groups

Java 3D provides several types of groups:

Group

BranchGroup

OrderedGroup

DecalGroup

SharedGroup

Switch

TransformGroup

All groups manage a list of children nodes

Shapes, lights, sounds, behaviors

Group Class Hierarchy

All groups share attributes inherited from the Group class

Groups

The Group class is the most general-purpose of the group nodes

Has exactly one parent

Can have any number of children

You can add, insert, remove, and get children in a group

Children are implicitly numbered starting with 0

Child rendering order is up to Java 3D!

Java 3D can sort shapes for better rendering efficiency

Group Class Methods

BranchGroups

A BranchGroup is a major sub-tree of the scene graph

Can be attached to a Locale

Can be compiled as a unit

Can be included as a child of a group node in another subgraph

Can be reparented or removed at runtime

Adding a BranchGroup to a Locale makes the group live

Once live, changes are constrained to those enabled by capabilities

BranchGroup extends the Group class

DecalGroup adds no additional methods beyond those of the OrderedGroup class

BranchGroup Class Methods

OrderedGroups

An OrderedGroup guarantees children are rendered in first-to-last order

Unlike Group, BranchGroup, etc.

Good for avoiding Z-fighting artifacts

OrderedGroup extends the Group class

OrderedGroup adds no additional methods beyond those of the Group class

BranchGroup extends the OrderedGroup class

DecalGroups

DecalGroup extends OrderedGroup and renders children in order

Children must be co-planar

First child is the underlying surface

The underlying surface must encompass all other children

Use for rendering decal geometry

Text

Texture Decals (eg, insignia on an airplane wing)

DecalGroup adds no additional methods beyond those of the OrderedGroup class

Switches

A Switch selects zero, one, or multiple children to render

Which child to render can be an integer child number, or bits in a mask

Similar to a Java "switch" statement

This node is only a switch, it does not imply any rendering order

Switch extends the Group class

Selecting Children

Select which child to render by its child index

Special values:

Render no children: CHILD_NONE

Render all children: CHILD_ALL

Or select a set of children with a bit mask

A value of CHILD_MASK enables mask use

Set a member of a Java BitSet for each child to render

Switch Class Methods and Examples

Sharing Groups of Shapes : SharedGroup Node

Some shapes occur over and over in a scene

Marble columns in a colonnade

Basic user interface components

Sharing enables you to create one master definition of a shape then link to it multiple times in the scene