Awesome

Adafruit_NeoMatrix. Whoa.

Adafruit_GFX-compatible library for NeoPixel matrices and grids. Controls single and tiled NeoPixel displays such as the Adafruit NeoPixel Shield or grids assembled from Adafruit 60 LED/meter Digital LED strip. Requires Adafruit_NeoPixel and Adafruit_GFX libraries.

After downloading, rename folder to 'Adafruit_NeoMatrix' and install in Arduino Libraries folder. Restart Arduino IDE, then open File->Sketchbook->Library->Adafruit_NeoMatrix->matrixtest sketch.