GLSL Shader Pipeline

Introduction

The SoShaderPipeline modules offer an extensible GLSL shader pipeline based on the SuperShader concept. The fragment and vertex shaders are divided into a dynamic shader pipeline, which allows for the interactive addition of custom shader code. A pipeline step is modeled as a subset of several shader pipeline functions that contain the GLSL shader code.

The main advantage over bare-metal GLSL shaders is that different aspects of the shader can be extended or exchanged without requiring adaptations to other parts of the shader. For example, you can add a new light model without having to handle the different number of fixed-function lights in the scene. The basic shader pipeline incorporates the following Open Inventor or OpenGL fixed function state:

• lighting (supporting all Open Inventor lights)
• fixed function texturing
• fog

Both the surface shading and the lighting model can be exchanged and/or extended separately.

Usage

The shader of a shader pipeline is generated and activated by placing a SoShaderPipeline module into the scene graph. If no other extensions are in the Open Inventor state, the generated shader will contain only the GLSL code that implements the fixed-function state of OpenGL at that position in the scene graph.

Any number of extensions can be placed in front of a SoShaderPipeline module and will be incorporated into the generated GLSL code. Extensions placed after a SoShaderPipeline module do NOT affect the created shader at all.

Since the shader pipeline is based on the GLSL shader framework, extensions can utilize the SoShaderParameter*, SoSampler*, SoImageFileSampler, and SoVertexAttribute* modules, taking advantage of the resulting uniforms and vertex attributes in the extensions.

Typical use cases for pipeline extensions are:

• Modifying the geometry
  • SoDrawInstanced
  • SoPointSpriteRenderer
• Exchanging the light model for a custom model
  • SoShaderPipelineLightModel
  • SoShaderPipelineCellShading
  • SoShaderPipelineToneShading
• Implementing a custom surface shader
  • SoShaderPipelineSurfaceShader
• Adding new light types (e.g., shadow-casting lights)
  • SoShadowMapping
• Modifying the result color or transparency
  • SoShaderPipelineSilhouette
• Extending the writing of the result color/normal
  • SoScreenSpaceAmbientOcclusion
  • SoDepthPeelRenderer
  • SoWeightedBlendedOIT
• Extending any step of the pipeline
  • SoShaderPipelineFunction
  • SoShaderPipelineInclude

Debugging/Development

The SoShaderPipelineDiagnosis module can be placed in front of a SoShaderPipeline module and will show the resulting shaders, errors/warnings, and all pipeline steps and includes.