learning - Academic Conferences Limited

Robert Lucas
However, in a real dissection, cuts are not usually made in a single action but are the result of a
number of incisions. Having successfully implemented the planar cutting algorithm with the associated
texture mapping to the cut surface, it is now possible to see how incisions can be implemented. A
knife blade can be represented as a 3D model and the collision between it and the object being cut as
well as the geometry of the blade can be used to calculate the appearance of the incision. The
incision can be implemented in much the same way as the cuts in the approach described above, but
now we will want to add in some behaviour of the cut material, such as how much it pulls back from
the blade to create a groove or valley in the cut surface. The sides of this groove can be constructed
as per our cut surface above. Some experimentation with how a ‘peeling back’ type operation can be
performed. We can identify a contact point and force from a dissection tool indicated by its movement.
We can warp a mesh differentially by moving its vertex positions along the direction of the force from
the tool whilst maintaining distances between adjacent vertices to maintain the surface integrity of a
substance like skin. We can even introduce some stretching if we need to. We can propagate the
force from the tool through the tissue being ‘peeled back’ so that points nearer the tool move the most
whilst those distant from the tool behave as though anchored. With a suitable controlling device, there
is no reason why we couldn’t offer some feedback to the user on the force required to perform an
incision or operation to move or peel-back an object. At this point we will be well on the way to
providing a realistic, if not total, dissection experience. This will be a very different experience from
that offered by current dissection packages as there will be no constraints on where you can put the
knife in, nor what you can put it into.
6. Conclusions
We cannot realistically expect to perform authentic dissections using 3D models in a games
environment without putting in place some algorithmic and representational solutions to some of the
many facets of the various processes that make up a dissection activity. This paper has shown how
we can achieve planar cuts on surface models that make them appear to be solid by cutting the faces
of the original object and replacing them with faces along the cut and filling the hole created by the
cut. It has also been shown that textures can be added to the cut face that can span many triangular
faces and present a coherent continuous texture that can be derived from a photograph to add extra
realism. It is proposed that these techniques can be extended to provide partial cuts or incisions. It is
asserted that these techniques take us a significant step towards performing virtual dissections using
standard tools available to games programmers.
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