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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="content-type">
<title>Java 3D 1.4 Shaders</title>
</head>
<body>
<h2>Shaders in Java 3D<sup><font size="-2">TM</font></sup> 1.4</h2>
<h4>Introduction and pointer to discussion forum</h4>
<p>If you wandered over here looking for a completed draft
programmable shading specification for
Java 3D<sup><font size="-2">TM</font></sup> 1.4 that you can
review, you are in the wrong place; or more accurately, the right
place at the wrong time. Come back in about 2 months and things should
be in state where you can review a fairly complete draft
specification. If, on the other hand, you'd like to help us define and
evolve the programmable shading API in Java 3D 1.4, please read
on.
</p>
<p>This is a very rough first draft of what we are thinking in terms
of programmable shader support in Java 3D 1.4. As we mentioned at
JavaOne, we plan to do the 1.4 API specification under the auspices of
the Java Community Process (JCP). However, we very much want to
involve the larger community in API discussions for programmable
shaders, so please join in the discussion.
</p>
<p>We have created a thread on the Java 3D discussion forum for
discussing <a
href="http://www.javadesktop.org/forums/thread.jspa?threadID=5056"
target="_blank">Java 3D Programmable Shaders</a>. Feel free to
post your comments on our ideas, or post some ideas of your own.
</p>
<h4>Class Hierarchy for Shader Objects</h4>
<p>The proposed class hierarchy for programmable shaders
in Java 3D is:</p>
<ul>
<li>Abstract shader base classes:</li>
<ul>
<pre>public abstract class ShaderProgram extends NodeComponent
public abstract class Shader extends NodeComponent
</pre>
</ul>
<li>Concrete GL2 shader classes:</li>
<ul>
<pre>public class GL2ShaderProgram extends ShaderProgram
method: {add/remove/get}Shader(GL2Shader) // set of shader objs
method: {add/remove}ErrorListener(GL2ErrorListener)
method: validate(Canvas3D) ???
public abstract class GL2Shader extends Shader
public class GL2VertexShader extends GL2Shader
method: set/getShaderSource(String)
method: validate(Canvas3D) ???
public class GL2FragmentShader extends GL2Shader
method: set/getShaderSource(String)
method: validate(Canvas3D) ???
</pre>
</ul>
<li>Concrete Cg shader classes:</li>
<ul>
<pre>public class CgShaderProgram extends ShaderProgram
method: {set/get}VertexShader(CgVertexShader)
method: {set/get}FragmentShader(CgFramentShader)
method: {add/remove}ErrorListener(CgErrorListener)
method: validate(Canvas3D) ???
public abstract class CgShader extends Shader
public class CgVertexShader extends CgShader
method: set/getShaderSource(String)
method: validate(Canvas3D) ???
public class CgFragmentShader extends CgShader
method: set/getShaderSource(String)
method: validate(Canvas3D) ???
</pre>
</ul>
<li>Changes to existing Appearance class (or maybe create new
ShaderAppearance subclass):</li>
<ul>
<pre>public class Appearance extends NodeComponent
...
method: set/getShaderProgram(ShaderProgram)
</pre>
</ul>
</ul>
<p>Click on the following link for a preliminary look at the <a
href="javax/media/j3d/ShaderProgram.html">javadoc-generated API
definitions</a> for the newly proposed classes. Note that this is only
the javadoc for the <i>new</i> classes. We know that there are lots of
broken links for the existing classes.
</p>
<h4>Example Usage</h4>
<p>This is an example code excerpt showing how one might use the new
programmable shader API in a Java 3D program.
</p>
<ul>
<pre>String vertexShaderFile = "my-vertex-shader-file-name";
String fragmentShaderFile = "my-fragment-shader-file-name";
String vertexShaderSource;
String fragmentShaderSource;
// Read CG vertex and fragment shader source code from text files
vertexShaderSource = TextFileUtils.readFully(vertexShaderFile);
fragmentShaderSource = TextFileUtils.readFully(fragmentShaderSource);
// Create CG vertex and fragment shader objects using the given source code
CgVertexShader vertexShader = new CgVertexShader(vertexShaderSource);
CgFragmentShader fragmentShader = new CgFragmentShader(fragmentShaderSource);
// Create the CG shader program object and attach the vertex and
// fragment shader objects; add an error listener
CgShaderProgram shaderProgram = new CgShaderProgram();
shaderProgram.setVertexShader(vertexShader);
shaderProgram.setFragmentShader(fragmentShader);
shaderProgram.addErrorListener(myCgErrorListener);
// Use CG shader program object in appearance
appearance.setShaderProgram(shaderProgram);
</pre>
</ul>
<h4>Shader Parameters</h4>
<p>Programmable shaders define two types of parameters: uniform and
varying. As the names imply, uniform parameters are constant (within a
primitive), while varying parameters can vary on per-vertex or
per-fragment basis.
</p>
<ol>
<li><b>Uniform parameters</b> (attributes) are those parameters whose
value is constant during the rendering of a primitive. Their values
may change from primitive to primitive, but are constant for each
vertex (for vertex shaders) or fragment (for fragment shaders) of a
single primitive. Examples of uniform parameters include a
transformation matrix, a texture map, lights, lookup tables,
etc. Several Java 3D state attributes are automatically available
to the shader program as pre-defined uniform parameters. The
application doesn't need to do anything to pass these parameters in to
the shader program. The implementation of each shader language (e.g.,
Cg, GL2) defines its own mapping from Java 3D attribute to uniform
variable name.<br>
<br>
We need additional API to allow applications to pass in uniform
parameters that do not correspond to a pre-defined Java 3D
attribute...<br> TODO: Finish this...<br>
<br>
A partial list of Java 3D attributes that are mapped to shader
attributes follows:
</li>
<br>
<table style="text-align: left;" border="1" cellspacing="2"
cellpadding="2">
<tbody>
<tr>
<td style="vertical-align: top; text-decoration: underline;">Java 3D
Attribute<br>
</td>
<td style="vertical-align: top; text-decoration: underline;">Cg
shader variable<br>
</td>
<td style="vertical-align: top; text-decoration: underline;">GL2
shader variable<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">ModelViewProjection<br>
</td>
<td style="vertical-align: top;">glstate.matrix.mvp<br>
</td>
<td style="vertical-align: top;">gl_ModelViewProjectionMatrix<br>
</td>
</tr>
<tr>
<td style="vertical-align: top;">Light[<i>n</i>] pos<br>
</td>
<td style="vertical-align: top;">glstate.light[<i>n</i>].position </td>
<td style="vertical-align: top;">gl_LightSource[<i>n</i>].position </td>
</tr>
<tr>
<td style="vertical-align: top;">...<br>
</td>
<td style="vertical-align: top;">...<br>
</td>
<td style="vertical-align: top;">...<br>
</td>
</tr>
</tbody>
</table>
<br>
<li><b>Varying parameters</b> are those parameters that are specified
as per-vertex attributes. They are are interpolated across a primitive
similarly to colors and texture coordinates in the fixed function
pipeline.<br>
<br>
We need additional API to allow applications to pass in per-vertex
varying parameters...<br> TODO: Finish this...<br>
</li>
</ol>
<p>TODO: more info here.
</p>
</body>
</html>
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