In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light.
A piece of milled plexiglass acting as a projecting lens; via the Computer Graphics and Geometry Lab at the École Polytechnique Fédérale de Lausanne
New milling techniques applied to glass and plexiglass panels could be used to “create windows that are also cryptic projectors, summoning ghostly images from sunlight.”
[Pauly and Bompas] hope that the technique will be used in architectural design, to create windows that mould sunlight and throw images or patterns onto walls or floors,” which, if timed, milled, and manipulated just right, could produce a slowly animated sequence of images being projected by an otherwise empty window during different times of day.
To control the shape of a caustic pattern generated by a specular or refractive surface, we need to solve the inverse problem: how can we change the surface geometry, such that incident light is redirected to produce a desired caustic image?
In my opinion, what makes a designer competent is precisely their ability to credibly justify their conclusions. If you can’t do this as a designer—no matter how successful your results are—then neither I nor anybody else can tell if you aren’t just picking things at random.
What I am proposing, then, is no less than to make a designer’s entire line of reasoning a matter of permanent record. On the surface is the familiar set of prescriptions, components, examples and tutorials, like you would expect out of any such artifact. Attached to every element, though, is a little button that says You click it, and it tells you. The proximate explanation will probably not be very satisfying, so you click on the next until you get to the end, at which point you are either satisfied with the explanation, or you aren’t.