Blog

Dear All,

We have finalized development of several major new features for Open CASCADE Technology 7.0.
The most essential changes -- removal of CDL and WOK -- have been raised to master branch of the OCCT Git repository last Friday, and we propose this version for public review, as "alpha" version of OCCT 7.0.

This article is aimed to give overview of the major changes already integrated, and give idea of the effort required to port existing code on the new version.

OCCT provides built-in Interactive Services based on own OpenGL-based Visualization component. The basic functionality consists of but not limited to presentation and selection of topological shapes (TopoDS_Shape), which are the key objects in OCCT, but also various presentations for arbitrary mesh data, text annotations and others. Nowadays it works on wide range of platforms, including mobile ones, supports custom GLSL programs, GPU-accelerated Ray Tracing, and plenty of other modern features.

However one might decide to use alternative Visualization component, for historical reasons or for project-specific features. One of the most popular and powerful among freely available visualization toolkits is VTK.

One of the most breaking changes in visualization component in OCCT 6.9.0 is complete reconsideration of selection mechanism. The new algorithm is designed to improve performance of dynamic selection of complex scenes by using effective 3D acceleration structures which are built only once and are autonomous from the camera.

Hello All,

The release of OCCT 6.9.0 is published.

The corresponding tag in Git is "V6_9_0".

Hi All,

At the moment OCCT OCAF persistence uses plugin mechanism, when library providing persistent functionality for particular subset of OCAF attributes is loaded dynamically at runtime by OCAF.
For that, the plugin library name and location must be properly defined with help of predefined set of environment variables and resource files.
This system is quite complex and not transparent, especially for beginners.

OCCT 3D viewer provides the way for rendering temporary presentations without redrawing previously drawn content.
This feature is designed to optimize viewer performance when only small part of the scene is changed dynamically, usually providing some feedback for user actions.

This article describes this functionality and its evolution in recent versions of OCCT.

In some cases when a rendered closed shell consists of faces with different colors, visual artifacts at the edge of faces appearing at a certain view angle (Fig. 1).

Fig. 1. The visual artifacts on a simple cube

The back-face culling mechanism allows removing these artifacts.

Since the version 6.8.0 of Open CASCADE the new algorithm called “Volume Maker” is available. This algorithm builds the elementary volumes (solids) from a set of connected, intersecting, or nested shapes. The algorithm can be useful for splitting solids into parts, or constructing new solid(s) from set of intersecting or connected faces or shells. The algorithm creates only closed solids. In general case the result solids are non-manifold: fragments of the input shapes (wires, faces) located inside the solids are added as internal sub-shapes to these solids. Non-closed faces, free wires etc. located outside of any solid are excluded from the result.

The Boolean Operator of Open CASCADE (≤6.8.0) allows treating of two and only two arguments (shapes) to process [1]: S1 (Object), S2 (Tool). In modeling tasks the very frequent situation is when multiple shapes are to be processed from both sides, Object and Tool. For example, when we have to make in a body of Object multiple cutouts, we need to pass to the Boolean Operator one shape as the Object and a set of shapes as a Tool. The developer has to organize a cycle for repetitive cut from the Object shapes of the Tool one by one. Besides the fact that it is inconvenient for the developer, it applies additional extra expenses in the form of auxiliary temporary data structures that are filled in each instance of Boolean Operator.

This post in devoted to improvement of performance of building part of Boolean operations. Though in most cases the most time-consuming is intersection part (89% of overall time spent for BO by all Open CASCADE tests), there are special cases where building part takes most of the time. As an example the test case perf bop boxholes is taken, in which relation between Intersection and Building Parts is 2.85 / 26.16. This case is remarkable for showing the performance of the modeler when working with big number of simple shapes.

Next version of OCCT will feature new mode of Boolean Operation Algorithm (BOA), called "Fuzzy". Fuzzy Boolean operations are the type of Boolean operations in which additional user-specified tolerance is used. This mode allows Boolean operations to handle robustly cases of touching and near-coincident entities of the argument shapes.