OpenCSG OpenCSG project is a library that does image-based CSG rendering using OpenGL.
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OpenGL library image rendering CSG rendering OpenCSG image-based CSG

OpenCSG Description

OpenCSG project is a library that does image-based CSG rendering using OpenGL. OpenCSG project is a library that does image-based CSG rendering using OpenGL. OpenCSG is written in C++ and supports most modern graphics hardware using Microsoft Windows or the Linux operating system. OpenCSG-1.1.0 is the current version.What is CSG, anyway? CSG is short for Constructive Solid Geometry and denotes an approach to model complex 3D-shapes using simpler ones. I.e., two shapes can be combined by taking the union of them, by intersecting them, or by subtracting one shape of the other. The most basic shapes, which are not result of such a CSG operation, are called primitives. Primitives must be solid, i.e., they must have a clearly defined interior and exterior. By construction, a CSG shape is also solid then.Image-based CSG rendering (also z-buffer CSG rendering) is a term that denotes algorithms for rendering CSG shapes without an explicit calculation of the geometric boundary of a CSG shape. Such algorithms use frame-buffer settings of the graphics hardware, e.g., the depth and stencil buffer, to compose CSG shapes. OpenCSG implements a variety of those algorithms, namely the Goldfeather algorithm and the SCS algorithm, both of them in several variants.Benefits:CSG is often used as fundamental modeling technique in CAD/CAM applications. Here, image-based CSG rendering is the key to interactively manipulate CSG shapes. Since OpenCSG renders even complex CSG shapes fast, it can be advantageously used in such applications.Raytracers such as PovRay have used CSG for shape modeling since long ago. Interactive modeling toolkits for such raytracers normally just ignore CSG commands, though. OpenCSG represents a valuable addition for such applications.Overall, up to the present CSG rendering has been hardly used in interactive applications, since the necessary algorithms are complicated and error-prone. We hope that by providing a free library that is easy to use, fast, and versatile, CSG rendering can be made more mainstream than it currently is.Usage:The interface of OpenCSG is very easy to use. There is only a single abstract class called OpenCSG::Primitive. A Primitive object has an attribute Operation that denotes whether the primitive is intersected or subtracted. To use OpenCSG, create a derived concrete primitive class by implementing the render() method.To actually do the CSG rendering, there is the function OpenCSG::render() that takes a std::vector as argument. The render function evaluates the CSG expression given by the array of primitives and initializes the z-buffer with the proper values for the CSG expression. The color buffer remains unchanged, so afterwards, you must shade the primitives in the array using a GL_EQUAL depth function.Note that the render function does not evaluate a generic CSG tree that also would contain unions of CSG shapes. It has been shown that a generic CSG tree can be converted into an equivalent set of CSG expressions that the render function can handle. OpenCSG does not contain the functionality for this conversion since, after all, it is a rendering library.What's New in This Release:· OpenCSG can now use OpenGL frame buffer objects as an alternative to pbuffers to do the internal CSG rendering calculations.· This potentially reduces the rendering overhead because no switching between different rendering contexts is required.· Several other bugs have been fixed.

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