This abstract class is the parent of classes that define a programmable graphics pipeline stage that composes a shader program.

There are five types of shader objects that can be added to a shader program. Any of these stages can be user defined.

• Vertex shader The vertex shader is executed once for each vertex (usually in parallel). The main purpose is to transform each vertex's 3D position from model space to projection space. Vertex shaders can manipulate properties such as position, color and texture coordinate, but cannot create new vertices.

• Tessellation control shader This shader accepts a list of vertices defined as a patch to control the amount of tessellation applied to the patch. Following the execution of this shader, a tessellator computes a set of triangles in a parametric space.

• Tessellation evaluation shader This shader is executed at least once for each vertex that was created by the tesselator in the parametric space. The TES takes the parametric coordinate and the patch data output by the TCS to generate a final position for the surface.

• Geometry shader The geometry shader acts on a complete primitive (triangle or line): it can modify existing primitives, it can insert (create) new primitives, it can remove (destroy) existing primitives.

• Fragment shader Fragment shaders compute color and other attributes of each fragment.

Note: Compute shaders are not part of the rendering pipeline. They represent a shader stage used entirely for computing arbitrary information.

Shader object nodes cannot be inserted directly in a scene graph. They must be added to the field shaderObject of an OIV.Inventor.Nodes.SoShaderProgram node.

A shader object is defined by the following properties:

• Source program, which is the shader's source code (see OIV.Inventor.Nodes.SoShaderObject.sourceProgram field),

• Uniform parameters set by the application (see OIV.Inventor.Nodes.SoShaderObject.parameter field),

• State (active or not) (see OIV.Inventor.Nodes.SoShaderObject.isActive field).

The source program can be specified either by a string containing the program source code, or by a filename which contains the program source code. How the sourceProgram field is interpreted depends on the field OIV.Inventor.Nodes.SoShaderObject.sourceType.

The supported shading language of the program source is OpenGL Shader Language (GLSL) . Furthermore, the Open Inventor shader API or VolumeViz shader API must be used to write any GLSL shader program. See ShaderAPI for detail.

Uniform parameters can be set through the OIV.Inventor.Nodes.SoShaderObject.parameter field. Uniform means, in the case of a vertex or geometry program, a value which is the same for all vertices in a primitive, and, in the case of a fragment program, a value which is the same for all fragments created by a primitive. Each uniform parameter is represented by an instance of a specific subclass of OIV.Inventor.Nodes.SoUniformShaderParameter. For example, an OIV.Inventor.Nodes.SoShaderParameter1i holds a single integer value. A uniform parameter has no effect if it is not valid, that is, if there is no corresponding name (identifier) in the GLSL source program. An OIV.Inventor.Nodes.SoShaderParameter1i must be used for each texture sampler in order to specify the texture unit and texture sampler uniform parameter name pair.

A vertex shader can also use vertex parameters, which are per-vertex data passed from the application to the vertex shader. Vertex parameters are represented by an instance of a specific subclass of OIV.Inventor.Nodes.SoVertexShaderParameter. For example, an OIV.Inventor.Nodes.SoVertexShaderParameter1f holds a set of floating point values and an OIV.Inventor.Nodes.SoVertexShaderParameter3f holds a set of OIV.Inventor.SbVec3f values. Vertex parameter nodes are property nodes (similar to materials or normals) and should be added directly in the scene graph, not in the shader object.

Tips:

• Set the environment variable OIV_GLSL_DEBUG to get the GLSL compile/link output in the console.

• If you set the environment variable OIV_SHADER_CHECK_INTERVAL, the shader source file is checked for a change every n seconds, where n is the value specified by the variable. This allows you to edit a shader source file without needing to restart your application after each shader modification.

FILE FORMAT/DEFAULT

This is an abstract class. See the reference page of a derived class for the format and default values.

EXAMPLE

Simple fragment shader with one uniform parameter:

SoFragmentShader fragmentShader = new SoFragmentShader();
fragmentShader.sourceProgram.Value = "filename.glsl";

SoShaderParameter1i parameter = new SoShaderParameter1i();
parameter.name.Value  = "data1";
parameter.value.Value = 1;
fragmentShader.parameter[0] = parameter;

SoShaderProgram shaderProgram = new SoShaderProgram();
shaderProgram.shaderObject[0] = fragmentShader;
root.AddChild(shaderProgram);

Reference