In the first of our new series of CG basics we look at the extrude function
This month we take a close look at the extrude tool
I f you’re new to CGI there are far too many tools to choose from in a dizzying array of software. This series aim is to break everything in CGI down to the very basics, so that every artist can be armed with the knowledge of which tool is best. The journey begins with the extrude function. the root of 3D creation Extrusion can change a single polygon into a box, a disc into a simple cup, or if reversed, a hole in a wall. Achievingt a successful extrude, which can then be built on to form more complex modelling functions, depends on how many edges or loops are added after the extrusion, as well as the source polygon itself.
Some software can perform multiple extrudes at once on a recurring command, which can create curved and twisting shapes with one click.
There are some things to be aware of when extruding, as with everything in 3D, best practice pays dividends. Make sure the extruded polygon is ideally a quad (four-sided polygon). While most CG applications do support extrusions on n-gons, polygons with more than four sides can create issues. This includes the dreaded overlap if the n-gon is being reduced in scale at the same time as it is being extruded.
It is not just polygons that can be extruded, edges can be and so can points/vertices. The mileage can vary from application to application, but edge extrusion is great for building out polygons when retopologising existing meshes from a 3D scan, for example, into a more ordered form for animation or rendering without artefacts.
Extrusions can be manipulated when they are being performed, either in rotation, translation or scale, this is how most basic ‘box’ modelling is done. Box modelling is a technique of starting any model, whether it is a dragon or a Ferrari from a six-sided cube, using the extrude tool to create basic topology (an arrangement of polygons in a mesh). Mastering the techniques of extrusion is the foundation for any good model.