How to get Touch.radiusVariance with new input system?

Unity Engine
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1

Hi all,

I’ve just migrated to Unity’s new input system and quickly realized that the new touch system no longer has a property for Touch.radiusVariance. I use this property to normalize input sizes for a range of iOS devices and without it I will be forced to rewrite a perfectly functional input class. It would be much simpler if I could recreate the radiusVariance property that Unity used in their old input system. Does anyone know how Unity calculated radiusVariance in the past?

2

After firing up a build that uses the old input system I was able to gather some data points from a few iOS devices:

iPad

  • DPI: 264
  • Diagonal Pixels: 2560
  • Aspect Ratio: 1.333333
  • Radius Variance: 5.21875

iPhone 12

  • DPI: 460
  • Diagonal Pixels: 2789
  • Aspect Ratio: 2.164103
  • Radius Variance: 6.065735

iPhone SE

  • DPI: 326
  • Diagonal Pixels: 1530
  • Aspect Ratio: 1.778667
  • Radius Variance: 6.411896

After recording a variety of touch inputs, it appears that Touch.radiusVariance = the difference between 2 sequential radii / 2.

Using the iPhone SE as an example, here are some possible Touch.radius sizes:

  • 12.82
  • 25.65
  • 38.47
  • 51.31
  • 64.13

The difference between each sequential radius is roughly 12.82, which also happens to be the minimum Touch.radius size for this device. If we take that difference and divide it by 2 we get 6.41, or, if recorded with double precision, 6.411896, which is the radiusVariance for this device.
i.e., radiusVariance = (38.47 - 25.65) / 2.

I feel that I am getting closer to a solution but am still unsure of how Unity determines the Touch.radiusVariance as well as the possible Touch.radius sizes for a device. For now, I will be able to set the radiusVariance by referring to a constant variable after verifying the user’s device. However, I am a bit uncomfortable with this solution since there might be devices that do not fall into the categories of devices I have recorded. I would much rather be able to dynamically determine the radiusVariance of a device based on the specifications of that device.

In the meantime, I am currently exploring the radius.sqrMagnitude and radius.normalized of Unity’s new input system. There seems to be very little documentation on these properties, but from what I can tell:

  • radius.sqrMagnitude = (radius.x * radius.x) + (radius.y * radius.y)
  • radius.normalized = radius / (√radius.sqrMagnitude)

If I can use these properties to determine the sequential difference of radii or the minimum Touch.radius then I should be able to gather the Touch.radiusVariance as well.

I will continue researching and if I come across anything interesting I will be sure to post it here.