Click toggle spi(n) toggle fl(y) hold (f)ore hold (a)ft

Toggle fl(y)/turn modes. To fly (f)ore/(a)ft, hold key down.

Based originally on Zach Reizner's 2013 WebGL example for the illiOctahedron. The spi(n) toggle releases the hold on the illiMath mouse rotator by Glenn Chappell and Chris Hartman 1994. Note that the center of the canvas is the dead-zone. The fl(y) toggle switches the center of rotation from the icosahedron's center to the observer's center, enabling her to fly (f)oreward and (a)ft by holding these keys down. This is a poor substitute for a proper 3 button mouse (or finger) now next to impossible in the byzantine chaos of the ECMA hegemony. However, luckily the device mode of Chrome, Firefox and Safari has no way to move her finger continuously anyway. Note that WebGL has a primitive clipping plane at the origin, which is used here to cut a window into the surface. GF 2nov2017