There are no matrix effects yet - adding some is planned though!
After WLED has a better settings and preset managing system I hope I will be able to introduce support for XY coords -> pixel index translation (and associated settings), which will make it possible to implement nice matrix effects
It would also be interesting to support more advanced geometric mappings besides ordinary (Cartesian) XY matrices. Polar coordinates would be particularly useful, to support layouts with concentric rings (angle + radius) or cylinders/spheres/cones. (2D wrapped surface, angle + height) And, of course, effects for XY or polar coordinate systems can be easily mapped onto each other.
I have written a number of (non-WLED) custom effects that use polar coordinates for Christmas tree lights. This allows, for example, vertical bands of color that are animated to move around the tree (or, with off-sets, a candy-cane / barber-pole effect) I’d love to port these to WLED to take advantage of the excellent Web UI and well-integrated components.
I suppose the easiest implementation would be to allow creation of a group of segments and map them onto coordinate systems which are then used by effects. (ex. An 8x16 matrix panel (or cylinder) would consist of 8 segments of 16 LEDs.)
More inspiration: Here’s a project that uses (true 3D) cylindrical coordinates, allowing for even cooler effects than what I’ve done. (However, it’s all pre-calculated for a fixed permanent layout.)
The author also has some neat 2D light artwork based on Fibonacci-number-based layouts. (Supporting these would require custom mapping support from physical to XY/polar coordinates.)