view.html

JAVA多媒体开发类库说明

 front.</LI><P>
 <LI>TRANSPARENCY_SORT_GEOMETRY - transparent objects are
 depth-sorted on a per-geometry basis.  Each geometry object of each
 transparent Shape3D node is drawn from back to front.  Note that
 this policy will not split geometry into smaller pieces, so
 intersecting or intertwined objects may not be sorted
 correctly.  The method used for determining which geometry is closer
 is implementation dependent.</LI><P>
 </UL>
 </UL>
 <b>Projection and Clip Parameters</b><P>
 The projection and clip parameters determine the view model's
 field of view and the front and back clipping distances.<P>
 <UL>
 <LI>Field of view - specifies the view model's horizontal
 field of view in radians, when in the default non-head-tracked
 mode. This value is ignored when the view model is operating
 in head-tracked mode, or when the Canvas3D's window eyepoint
 policy is set to a value other than the default setting of
 RELATIVE_TO_FIELD_OF_VIEW.</LI><P>
 <LI>Front clip distance - specifies the distance away from the
 clip origin, specified by the front clip policy variable, in
 the direction of gaze where objects stop disappearing. Objects
 closer than the clip origin (eye or screen)
 plus the front clip distance are not drawn. Measurements are
 done in the space (physical or virtual) that is specified by
 the associated front clip policy parameter.</LI><P>
 <LI>Back clip distance - specifies the distance away from the
 clip origin (specified by the back clip policy variable) in the
 direction of gaze where objects begin disappearing. Objects
 farther away from the clip origin (eye or
 screen) plus the back clip distance are not drawn.
 Measurements are done in the space (physical or virtual) that
 is specified by the associated back clip policy
 parameter. The View object's back clip distance is ignored
 if the scene graph contains an active Clip leaf node.</LI><P>
 There are several considerations to take into account when
 choosing values for the front and back clip distances.<P>
 <UL>
 <LI>The front clip distance must be greater than 0.0 in physical
 eye coordinates.</LI><P>
 <LI>The front clipping plane must be in front of the back clipping
 plane, that is, the front clip distance must be less than the
 back clip distance in physical eye coordinates.</LI><P>
 <LI>The front and back clip distances, in physical eye coordinates,
 must be less than the largest positive single-precision floating
 point value, Float.MAX_VALUE. In practice, since these physical
 eye coordinate distances are in meters, the values
 should be much less than that.</LI><P>
 <LI>The ratio of the back distance divided by the front distance,
 in physical eye coordinates, affects Z-buffer precision. This ratio
 should be less than about 3000 to accommodate 16-bit Z-buffers.
 Values of 100 to less than 1000 will produce better results.</LI><P>
 </UL>
 Violating any of the above rules will result in undefined behavior.
 In many cases, no picture will be drawn.<P>
 </UL>
 <b>Frame Start Time, Duration, and Number</b><P>

 There are five methods used to get information about system
 execution and performance:<P>
 <UL>
 <code>getCurrentFrameStartTime</code> returns the time at which 
 the most recent rendering frame started.<P>
 <code>getLastFrameDuration</code> returns the duration, in milliseconds, of
 the most recently completed rendering frame.<P>
 <code>getFrameNumber</code> returns the frame number for this view.<P>
 <code>getMaxFrameStartTimes</code> retrieves the implementation-dependent
 maximum number of frames whose start times will be recorded by
 the system.<P>
 <code>getFrameStartTimes</code> copies the last k frame start time values
 into the user-specified array.<P>
 </UL>
 <b>View Traversal and Behavior Scheduling</b><P>
 The following methods control the traversal, the rendering, and
 the execution of the behavior scheduler for this view:<P>
 <UL>
 <code>startBehaviorScheduler</code> starts the behavior scheduler 
 running after it has been stopped.<P>
 <code>stopBehaviorScheduler</code> stops the behavior scheduler after all
 currently-scheduled behaviors are executed.<P>
 <code>isBehaviorSchedulerRunning</code> retrieves a flag that indicates
 whether the behavior scheduler is currently running.<P>
 <code>startView</code> starts traversing this view and starts the renderers
 associated with all canvases attached to this view.<P>
 <code>stopView</code> stops traversing this view after the current state of
 the scene graph is reflected on all canvases attached to this
 view.<P>
 <code>isViewRunning</code> returns a flag indicating whether the traverser
 is currently running on this view.<P>
 </UL>
 Note: The above six methods are heavy-weight methods intended
 for verification and image capture (recording). They are not
 intended to be used for flow control.<P>

 <b>Scene Antialiasing</b><P>

 The following methods set and retrieve the scene antialiasing
 flag. Scene antialiasing is either enabled or disabled for this
 view. If enabled, the entire scene will be antialiased on each
 canvas in which scene antialiasing is available. Scene
 antialiasing is disabled by default.<P>
 <UL>
 <code>setSceneAntialiasingEnable</code> sets the scene antialiasing flag.<P>
 <code>getSceneAntialiasingEnable</code> returns the scene antialiasing
 flag.<P>
 </UL>
 Note that line and point antialiasing are independent of scene 
 antialiasing. If antialiasing is enabled for lines and points, 
 the lines and points will be antialiased prior to scene antialiasing.
 If scene antialiasing is disabled, antialiased lines and points will
 still be antialiased.
 <p>
 <b>Note:</b> Scene antialiasing is ignored in pure immediate mode,
 but is supported in mixed-immediate mode.
 <p>
 <b>Depth Buffer</b><P>

 The following two methods enable and disable automatic freezing
 of the depth buffer for objects rendered during the transparent
 rendering pass (that is, objects rendered using alpha blending)
 for this view. If enabled, depth buffer writes are disabled
 during the transparent rendering pass regardless of the value
 of the depth-buffer-write-enable flag in the RenderingAttributes
 object for a particular node. This flag is enabled by default.<P>
 <UL>
 <code>setDepthBufferFreezeTransparent</code> enables depth buffer freezing.<P>
 <code>getDepthBufferFreezeTransparent</code> retrieves the depth buffer
 flag.<P>
 </UL>
 Transparent objects include BLENDED transparent primitives
 and antialiased lines
 and points. Transparent objects do not include opaque objects
 or primitives rendered with SCREEN_DOOR transparency.<p>

 <b>Sensors</b><P>

 The following methods retrieve the sensor's location in the
 virtual world:<P>
 <UL>
 <code>getSensorToVworld</code> takes the sensor's last reading and
 generates a sensor-to-vworld coordinate system transform. This
 Transform3D object takes points in that sensor's local coordinate
 system and transforms them into virtual world coordinates.<P>

 <code>getSensorHotSpotInVworld</code> retrieves the specified sensor's
 last hotspot location in virtual world coordinates.<P>
 </UL>

 <b>Compatibility Mode</b><P>

 A camera-based view model allows application programmers to think
 about the images displayed on the computer screen as if a virtual
 camera took those images. Such a view model allows application
 programmers to position and orient a virtual camera within a
 virtual scene, to manipulate some parameters of the virtual
 camera's lens (specify its field of view), and to specify the
 locations of the near and far clipping planes.<P>
 Java 3D allows applications to enable compatibility mode for
 room-mounted, non-head-tracked display environments, or to disable
 compatibility mode using the following methods. Camera-based
 viewing functions are only available in compatibility mode.<P>
 <UL>
 <code>setCompatibilityModeEnable</code> turns compatibility mode on or off.
 Compatibility mode is disabled by default.<P>
 <code>getCompatabilityModeEnable</code> returns the compatibility mode
 enable flag.<P>
 </UL>
 Use of these view-compatibility functions will disable some of
 Java 3D's view model features and limit the portability of Java
 3D programs. These methods are primarily intended to help
 jump-start porting of existing applications.<P>

 Setting the Viewing Transform<P>

 The View object provides the following compatibility-mode
 methods that operate on the viewing transform.<P>
 <UL>
 <code>setVpcToEc</code> a compatibility mode method that 
 specifies the ViewPlatform
 coordinates (VPC) to eye coordinates viewing transform.<P>
 <code>getVpcToEc</code> returns the VPC.<P>
 </UL>
 Setting the Projection Transform
 <p>
 The View object provides the following compatibility-mode
 methods that operate on the projection transform:<P>
 <UL>
 The <code>setLeftProjection</code> and <code>setRightProjection</code> 
 methods specify
 a viewing frustum for the left and right eye that transforms
 points in eye coordinates to clipping coordinates.<P>
 
 The <code>getLeftProjection</code> and <code>getRightProjection</code> 
 methods return
 the viewing frustum for the left and right eye.<P>
 </UL>

 <p>
 <b>Additional Information</b>
 <p>
 For more information, see the
 <a href="doc-files/intro.html">Introduction to the Java 3D API</a> and
 <a href="doc-files/ViewModel.html">View Model</a>
 documents.
<P>

<P>
<DL>
<DT><B>See Also:</B><DD><A HREF="../../../javax/media/j3d/Canvas3D.html" title="class in javax.media.j3d"><CODE>Canvas3D</CODE></A>, 
<A HREF="../../../javax/media/j3d/PhysicalBody.html" title="class in javax.media.j3d"><CODE>PhysicalBody</CODE></A>, 
<A HREF="../../../javax/media/j3d/PhysicalEnvironment.html" title="class in javax.media.j3d"><CODE>PhysicalEnvironment</CODE></A>, 
<A HREF="../../../javax/media/j3d/ViewPlatform.html" title="class in javax.media.j3d"><CODE>ViewPlatform</CODE></A>, 
<A HREF="../../../javax/media/j3d/TransparencyAttributes.html" title="class in javax.media.j3d"><CODE>TransparencyAttributes</CODE></A></DL>
<HR>

<P>
<!-- =========== FIELD SUMMARY =========== -->

<A NAME="field_summary"><!-- --></A>
<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
<B>Field Summary</B></FONT></TH>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE>static&nbsp;int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../javax/media/j3d/View.html#CYCLOPEAN_EYE_VIEW">CYCLOPEAN_EYE_VIEW</A></B></CODE>

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Specifies that monoscopic view generated should be the view as seen
 from the 'center eye', the fictional eye half-way between the left and
 right eye.</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE>static&nbsp;int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../javax/media/j3d/View.html#HMD_VIEW">HMD_VIEW</A></B></CODE>

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Specifies that the viewing environment for this view is a
 head-mounted display environment.</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE>static&nbsp;int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../javax/media/j3d/View.html#LEFT_EYE_VIEW">LEFT_EYE_VIEW</A></B></CODE>

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Specifies that monoscopic view generated should be the view as seen
 from the left eye.</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE>static&nbsp;int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../javax/media/j3d/View.html#NOMINAL_FEET">NOMINAL_FEET</A></B></CODE>

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Specifies a policy whereby the origin of physical or virtual
 coordinates is relative to the position of the nominal feet.</TD>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE>static&nbsp;int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../javax/media/j3d/View.html#NOMINAL_HEAD">NOMINAL_HEAD</A></B></CODE>