Cite the Google C++ Style Guide
Cite "Programming with Objective-C"
Extract class BTCube and simplify camera state
Organize methods
A more helpful triangle
Fix cube size, now centered
Fix "winding" of cube faces
fixup cube size
Set openGLView depthSize="24bit"

Without "asking for a depth buffer", `GL_DEPTH_TEST` has
no discernable effect.
Bigger plane