Greetings Friends of VR,
It's my opinion that a clearer relationship between "Pixel Density" and your VR device's resolution should be made, and it's my intention with this post to - hopefully - make it clearer so folks can use this setting to their advantage.
Right now iRacing allows us to adjust the VR Pixel Density in the renderDX11.ini file. It's set to 150 by default. What does that number really represent? Great question! A Pixel Density (PD) of 100 is really a resolution value, and that value is the native screen resolution your VR device; with the CV1 and Vive it's 2160x1200 and with the DK2 it's 1920x1080. Therefore, when you set the PD to 100 you are simply running your VR application at the device's native resolution.
Ok, Derek, tell me what happens when the PD is set to 150? I will! When you set the PD to 150 you "upscale" your device's resolution to a value of 1.5 times what it is natively. In the case of the CV1 it's 2160*1.5 x 1200*1.5, or 3240x1800. Make sense? It should...
So, then you can see what happens when you run the PD to 200. There you'd have a 2160*2 x 1200*2, or 4320x2400 resolution running. You can see another relationship emerging as well, and that's that the total number of pixels being rendered increases exponentially to the increase in PD.
Here are the total Pixels for popular values:
- PD = 100 => 2160x1200 resolution = 2,592,000 pixels
- PD = 150 => 3240x1800 resolution = 5,832,000 pixels
- PD = 200 => 4320x2400 resolution = 10,368,000 pixels
- PD = 250 => 5400x3000 resolution = 16,200,000 pixels
What I recommend personally to anyone is that they keep their PD value to whatever number gives that a solid 90 base simulation frame rate. If you ramp it up too aggressively you run the risk of frame rate degradation to the degree that ATW cannot compensate and you get ghosting, judder and, worse, VR induced disorientation and discomfort.
We can also draw a parallel for those who make the "Will this run iRacing in VR" threads. Say "iRving iRacer" has a three screen setup and he wants to know if his PC will "run iRacing in VR". He can easily run test laps at his various tracks and run a framerate test on each one. If he has frame rates running at ~90 or more all the time then he knows with ease that he can - should - run iRacing with VR; e.g.:
- iRving runs three screes at 1920x108 x 3 => 5760x1080 resolution = 6,220,800 pixels generated. If iRving can run that then he "should" have a good VR experience as his PC has enough power to do it.
I hope this helps folks understand the relationship between Pixel Density, Screen Resolution and expected pixels per frame more clearly.
NB: You can also see that if you're running a PD of 150 and generating a total of 5,832,000 pixels per frame cycle, then if you're getting 90fps you're generating a whopping 524,880,000 pixels per second! WOW!