Repetition

Many copies of one object on a grid with FiniteRepetition; here a mesh, the happy Buddha. The source is at Examples/Repetition/main.cpp.

Important

The default mesh comes from the common-3d-test-models git submodule. Clone with --recurse-submodules, or run git submodule update --init in the repository (see Obtaining EBGeometry); otherwise pass a mesh of your own as the first argument.

Repeating a mesh

The mesh is read into a TriMeshSDF, scaled to height 1 and stood on \(y = 0\) with Scale and Translate. FiniteRepetition(object, period, lo, hi) tiles it with the given period, lo and hi tiles to either side of the home tile along each axis:

const Expr grid = FiniteRepetition(statue, Vec3(0.8, 1, 0.8), Vec3(3, 0, 3), Vec3(3, 0, 3));   // 7 x 7

The tape stores the object once and evaluates it as a sub-program: each point is folded into the tile it lies in, and only the copies whose boxes come closer than that copy’s value are evaluated after it.

Against a union of copies

The program also places the same 49 copies one by one with Translate in a Union, which the tape evaluates through a BVH over their boxes (see BVH-accelerated unions). Both give the same values; the program prints each tape’s number of clauses, which grows with the copies only for the union, and the time per point of each.

Looking at it

The example ends with Render::view(repeated, pool, argc, argv), a window on the grid of statues.

The window needs SDL2 and is built with make VIEWER=SDL2 or cmake -DEBGEOMETRY_VIEWER=SDL2 (see The viewer window (EBGEOMETRY_VIEWER)); otherwise, and with --no-view or without a display, view() prints why and returns. Drag to orbit and scroll to zoom; the window lists its other keys (see The viewer’s keys).

Building and running

See Building for how to compile it with CMake, GNU Make, or a direct compiler invocation. Built for a GPU (see Running on a GPU), the window renders on the device.

cd Examples/Repetition
./Repetition.ex