xch_graph

xch_graph attribute values

There are four forms of the xch_graph attribute. The first form loads a VRML scene. The ‘href’ attribute specifies which scene to load. Here is an example of this form:

<img xch_graph=load href="http://www.chaco.com/vrml/room.wrl">

This form may also be used to load a 2-dimensional graphic into the graphics pane, by specifying a .jpg, .gif, or .bmp file to load. For example:

<img xch_graph=load href="http://www.chaco.com/room.gif">

The second form causes the current graphics image to be drawn before the client proceeds. It's useful after modifying a VRML node, to force the graphics module to draw what you've sent it immediately. Here is an example of this form:

<img xch_graph="draw">

The third form causes the graphics pane to be hidden:

<img xch_graph=hide>

The last form of the xch_graph command changes the value of a field in the current VRML scene by sending a “set_fieldName” event to the VRML viewer. There are two ways that you can do this:

<img xch_graph="event nodeName fieldType eventName args">

<img xch_graph="event nodeName fieldType eventName args" xch_graph_vrml="vrml code">

where the values are as follows:

nodeName	is any node named by the DEF keyword. It may also may be a period-delimited qualified name, such as MySeparator.MyRotation
fieldType	is the VRML type of the field to change. Currently supported are SFRotation, SFLong, SFVec3f, and SFNode. This must correspond to the correct field type of the field to be changed. See the VRML spec for descriptions of the SFRotation, SFLong, and SFVec3f field types. Type SFNode corresponds to a single node, and is specified by either name (for an existing node to be operated upon) or VRML code (for a new node to be added).
eventName	name of the event to send. This is usually the name of the field to change, prepended by “set_”.
args	arguments to the field change event.
vrml code	is actual VRML code to be used in the event. Do not precede it with the standard VRML 1.0 header, this is assumed. This code is compiled and then used by the event, such as adding it as a child node. It must compile to one top-level node. That node may have any number of children, of course. To use embedded double quotes, such as those around SFString fields, use HTML entities for the quotation marks, either ‘"’ or ‘"’. Note: You should keep this code as short as possible through the use of WWWInline nodes. There is a limit of 4,000 characters for each HTML tag.

The following table lists the currently supported events, their types, and their arguments.

Event Name	Node Types Affected	Event Type	Field Affected & (comments)	Arguments
add_children	Separator Group Switch	SFNode	(add a child)	No args; VRML code should be supplied as the argument to xch_graph_vrml. See the note below regarding the types of nodes which can be added.
remove_children	Separator Group Switch	SFNode	(remove a child)	Name of child to remove. See the note below regarding the types of nodes which can be added.
set_center	Transform	SFVec3f	center	new center vector
set_rotation	Transform Rotation SpinGroup	SFRotation	rotation	new rotation, as four floats: xAxis, yAxis, zAxis, angle
set_scaleFactor	Transform Scale	SFVec3f	scaleFactor	new scale vector
set_scaleOrientation	Transform	SFRotation	scaleOrientation	new orientation rotation
set_translation	Transform Translation	SFVec3f	translation	new translation vector
set_whichChild	Switch	SFLong	whichChild (to select a child of the switch)	number of child, zero-based

Note: It is only permissible to add or remove nodes which do not ‘leak’ state to other portions of the scene graph. The following node types can not be added or removed directly:

Background	BaseColor	Environment	Group
Coordinate3	Info	FontStyle	Material
MaterialBinding	MatrixTransform	Normal	NormalBinding
Rotation	Scale	ShapeHints	Texture2
Texture2Transform	TextureCoordinate2	Transform	Translation

It is legal to add a leak-proof parent node with these types as children. We recommend that you add or remove Separator nodes, and include all other nodes as children of the Separator node being modified.

Examples

The following code loads a 2-dimensional JPEG image into the graphics pane:

<img xch_graph=load href="http://www.chaco.com/~coyote/graf/smronny.jpg">

This example loads a 3-dimensional scene into the graphics pane:

<img xch_graph=load href="http://bradley.bradley.edu/~dware/mystars.wrl">

This example sets the current viewpoint to camera #1. It assumes the standard VRML convention that there is a Switch node called Cameras. (Note that not all VRML files have such a node.)

<img xch_graph="event Cameras SFLong set_whichChild 1">

The following adds a VRML node to a Separator node. By placing a Transform inside the new Separator, we’ve made it possible to manipulate the location of the contents of the WWWInline later. Fetching of the WWWInline will start immediately after adding this new sub-tree to the VRML scene.

<img xch_graph="event MyRoot SFNode add_children" xch_graph_vrml="DEF MyGreenCylinder Separator{DEF MyTransform Transform {} WWWInline {name mycylinder.wrl} AsciiText { string &quot;It's Ralph&quot; } }">

The following changes the rotation affecting the WWWInline child added above.

<img xch_graph="event MyRoot.MyGreenCylinder.MyTransform SFRotation set_rotation 0. 1. 1. 1.">

To send multiple lines of VRML in one "add_children" event, use HTML "encodings". The HTML encoding for a linefeed is "&#10;", so to send the following VRML code on multiple lines, you would use a construct like this:

<img xch_graph="event AvatarRoot SFNode add_children" xch_graph_vrml="DEF MyGreenCylinder Separator { &#10;

WWWInline { name m1red.wrl.gz } }" >

Note that you may want to use xch_mode=purehtml for these multiple line VRML code fragments. See the xch_mode documentation for more information.

Also see

event

xch_mode