Hi guys,

I can try to give this a go, but I would love to hear what’s the rationale of using this with the texture sizes though.

So: my assumption is that the course talks about “retina” level quality of textures. Retina here possible refers to Apples trademark where pixel density per length unit (PPI pixels per inch or PPCM pixels per centimeter) is minimum ~300 PPI. This is so to speak a sharpness or crispiness “value”. If I have understood correctly this is the amount of pixels needed so human eye cannot distinct separate pixels.

Distance is a factor here too. Moving display closer or further away either increases or decreases the amount of density required. The original ~300 PPI was calculated by holding a device from 10 inch from your eyes. So to take the distance into account there’s another measurement called Pixel Per Degree (PPD). So for example 57 PPD means that a triangle with a height equal to the viewing distance and a top angle of one degree will have a base on the device’s screen that covers 57 pixels.

The formula of PPD is 2dr * tan(0.5 degrees) where d = distance, r = pixel density per length unit.

So with 300 PPI device held on 10 inches from the eyes: 2 * 10 * 300 * tan(0.5) = 52.4 (rounded). If 300 PPI is enough (from 10 inches) to achieve retina level resolution then the respective PPD is 52.

(if you wonder what the 57 (used in the resource excel) is, that’s the PPD of an iPhone5 = 2 x 10 x 326 * tan(0.5) = 56.89 (rounded to closest whole number)

Eventually, I am guessing that the mistake here is (like @rekov pointed out) is that course uses radians. So, example:

2 * 10 * 299 * tan(0.5 rad) = **3266**.88 PPD

So the idea probably was to use this constant for max resolution when using size and distance so that the result would be best possible. But from there on I am lost. I don’t know what is tan(size/distance) either in angles or degrees. It’s looks like some sort of ratio multiplier but dunno.

I am running out of time now, hopefully this helps. I might be completely wrong too so I am merely guessing what might be going and I would love to hear what is the actual idea behind the formula.

Cheers, Jax