The BIAS OpenGL rendering framework is used to visualize generated 3D models and for Analysis-by-Synthesis algorithms.

It is capable to render models, images and 3D primitives in onscreen or offscreen contextes using given camera parameters, following the definition of the camera parameters and projections in BIAS/Geometry, (see Geometry / Transformations), including radial distortion.

Rendering Contexts

There are 3 main render contextes which can be used to render objects. Two onscreen and own offscreen context. The render contextes share a common interface and the base class is BIAS::RenderContextBase. From BIAS::RenderContextBase the other contextes BIAS::ContextWX, BIAS::ContextGLUT and BIAS::ContextPBuffer are derived.

The BIAS::ContextWX is a context derived from wxGLCanvas which is used in WxWidgets applications to render BIAS models directly in WxWidgets applications using the projection parameters from BIAS.
The BIAS::ContextGLUT is a glut context which provides BIAS parameter rendering in combination with GLUT.
The BIAS::ContextPBuffer used a pbuffer to render objects in an offscreen pbuffer context. This is very useful for Analysis-by-Synthesis approaches in which real images are compared to their rendered correspondences.

In BIAS::RenderContextBase a pointer to BIAS::GLProjectionParametersInterface is stored which holds the rendering parameters. See the next section for a desciption of the projection parameter concept.

Camera Parameters

The camera parameters in the BIAS OpenGL rendering framework follow the definition of BIAS::ProjectionParametersBase (see Camera Projection Concept) and the derived classes and are represented as "GLProjectionParameters". The class hierarchy is defined as follows:

A main interface class BIAS::GLProjectionParametersInterface is used as generic interface between rendering contextes, controllers and camera parameters. Every GLProjectionParameter... class is derived from BIAS::GLProjectionParametersInterface and the real BIAS::ProjectionParametersBase object pointer can be obtained by calling the BIAS::GLProjectionParametersInterface::GetMyselfAsProjectionParametersBase() function. The only camera paramter class currently implemented in BIAS is BIAS::ProjectionParametersPerspective which is capable to represent the standard projection matrix such as BIAS::PMatrix including radial distortion parameters.

Scenes

The representation of things that are to be drawn OpenGL is organized as a hierarchy of "Scenes" in BIAS. There is a base class called BIAS::SceneBase from which all other scenes are derived. The BIAS::RenderContextBase holds a vector of pointers to SceneBase objects. The central function in BIAS::SceneBase is the Draw() function in which for example OpenGL operations can be used to draw things in OpenGL.

BIAS::SceneBGImage is a background image scene which is used to show images as backgrounds. BIAS::RenderContextBase has a special pointer to such a background image scene.
BIAS::SceneThreeDOutWrapper wraps a BIAS::ThreeDOut object and is used to render the contents of such an object in OpenGL
BIAS::SceneOpenSceneGraph is a wrapper for OpenSceneGraph in BIAS
BIAS::SceneText is used to render text in 3D
BIAS::SceneGlutPrimitives uses GLUT to render primitives such as boxes or teapots
BIAS::ScenePointLight represents a point light and is used for illumination
BIAS::SceneSimpleQuad is an example to show how to draw a simple quad.

To implement your own scene just derive from BIAS::SceneBase and overload the Draw() method.

Controller

In many applications using a GUI it is desirable to manipulate the current viewpoint to view the shown 3D content from another perspective or to edit the content or to make screenshots of the current view. For this purpose the BIAS uses "Controllers". Every controller has a controlled object which is mostly a BIAS::GLProjectionParametersInterface object. All controllers are derived from a common base class, the BIAS::ControlInterface.

BIAS::FlyControl implements the known fly controller.
BIAS::TrackballControl implements the known trackball controller.
BIAS::AutoControl is a controller for autopilot modus.
BIAS::OnlyRotationControl allows only to change the rotation of the camera.
BIAS::TrackballTransControl allows only to change the translation of the camera.
BIAS::DistanceMeasureControl is as the TrackballControl but additionally allows only to measure distances by double clicking scene points.
BIAS::ScreenShotListener is a special controller which is used to take screenshots.

OpenGL Viewers

There are two viewers currently implemented in BIAS to display 3D models. The first is based on the ContextGLUT and called biasGLviewerGLUT (see biasGLviewerGLUT.hh and biasGLviewerGLUT.cpp). The second is based on the ContextWX and called biasGLviewerWx (see biasGLviewerWx.hh and biasGLviewerWx.cpp). If BIAS is compiled with the OpenSceneGraph library (http://www.openscenegraph.org/) the viewers can be used to display all kinds of 3D models which are supported by OpenSceneGraph.

Author: Ingo Schiller