Coordinate Representations

2 or 3 coordinate points?

• Performance cost of extra coordinate is not very high
  • Apple now uses two float64 coordinates, larger than 3 float32s
• VR/AR are growing industries
  • Choosing 2D points now requires breaking compatibility with everything to change in the future
  • 3D points work perfectly fine for 2D also, the 3rd coordinate can just be ignored

Floating or fixed point?

• Android uses integer coordinates, iOS floating point.
• Floating point can deal with large values without overflow (but losing precision)
  • Overflow not likely to be an issue with most UIs (and 32 bit fixed point)
• Big issue is rounding/pixel exactness
  • May be desirable for edges of ex. rectangular buttons to lie on pixel boundaries
    • If no pixel exactness, one edge of button may be soft and other edges hard
    • More noticeable on non-high-dpi monitors
  • Some drawing could be cached in an image, and it's better for cached images to be drawn pixel-exactly
  • Achievable with floats by calling floor() etc at appropriate times
    • But one mistake may make subsequent calculations off
    • There may also be coordinate-scaling transforms applied
  • In some circumstances pixel-exact rendering is infeasible and so rounding is undesirable
    • Rendering in 3D space, or under certain scaling transformations
    • Rounding can be effectively turned off under fixed point, by choosing a very high virtual DPI