SECTION 9 - Miscellaneous

10] What's a Blob?
(From Blob Sculptor documentation)

In 1982 J.F. Blinn modeled molecular shapes using an object which consisted of a point (the center of the object) and a radial field which decayed exponentially as a function of the distance between any given point in space and the center of the object. A test point near to the center of this object would have a very high potential field. As this point was moved outward, its potential field would reduce until, at a given distance R (the radius) it would go to zero. This object is called a "Blob".

Blobs consists of an arbitrary number of objects, called "components" which interact with each other. A "spherical component" is a blob component which has the geometry of a sphere (there are cylindrical, and conical components too!). In order to find the interaction between all the components of a given blob, a test point in 3D space is evaluated in terms of the potential field that EACH component contributes. The individual potential field of a component is called it's "density" or "strength". This strength can be positive or negative. Once all the contributions of all the components for a given test point are calculated, they are added up. Since some of the strengths may be positive or negative, the object may or may not have a value at the test point.

Finally, in order to know if that point in the object will be part of the final surface, the total strength of that point is compared against a "threshold" value. If the strength >= threshold then the point exists, else it dissapears. The threshold value can be thought of as a filter; the higher the threshold, the stronger the blob component must be in order to visible.

Once all the points in space are calculated, an algorithm called "marching cubes" is used to convert this 3D values into surfaces.

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