Parallel projections option renders too big vertical FOV and 25% performance is lost



Pimax 5k+ without option parallel projection has vertical FOV 103…104 degree (see All the different FOVs of Pimax 5k+).
If i see with my camera through lenses i also see 103…104 degree. It’s for all horizontal mode (Large, Normal, Small).

With enabled parallel projection option vertical FOV is 116 degree!!! But my camear through lenses also see only 103…104 degree. And also for all horizontal FOV (Large, Normal Small).
Horizontal FOV - rendered and displayed is same for all FOV mode!!!

To compare there is rendered Headset Mirror RAW images for Small FOV (there are no large distortions and the argument about the necessity of calculating the superfluous image is not correct).
Parallel projections ENABLED

Parallel projections DISABLED

6 degree up and 6 degree down image you just not see in HMD. It’s just not correct vertical FOV. And it renders an extra 25% of the image that is not visible.

Correct parallel projections image must be this:


In this image you see, that with same vertical resolution central circle has 25-26% more size and more resolution.
The big difference in performance with parallel projection not only in the rendering method, but also in the difference in the vertical angle.
Pimax - please just fix it and give us 25% more performance.

P.S. HTC Vive, Oculus and other HMD used only parallel projection. And it’s not used excess FOV for rendering:
HTC Vive rendered parallel projection

HTC Vive displayed image:

P.P.S. And one more. For games with double visions with parallel projections just give offset images adjust (like big ipd offset adjust), that fixed this double vision (it’s just decrease horizontal FOV). Maybe it’s same offset for all games with double visions.

@Sean.Huang, @Doman.Chen, @Dallas.Hao, @Pimax-Support, @xunshu

All the parallel FOVs of Pimax 5k+
VRMAN66: Pimax 5k+ review: Impressions and Measurements
All the different FOVs of Pimax 5k+

the PP rendered picture is supposes do be bigger and after putting it back in to perspective to the angled displays it looks the same as a non PP picure (so lens shots for PP on and off look the same)


Yes, indeed, in the parallel-projection mode, the rendering is much wider!
A lot of extra both on the vertical FOV and on the horizontal FOV.

Here’s a visual difference (PiTool 1.0, Large FOV, SS = 80%), SteamVR Mirror:

Without PP:

With PP:

Hence all the performance problems with parallel projections. (Although I do not particularly notice it on the vertical FOV.)


HTC Vive, Oculus and other HMD used PP and rendered FOV and displayed FOV almost same.
Pimax 5k+ with PP also has same displayed horizontal FOV: rendered and displayed.


Wider image with parallel projections it’s not Pimax issue. This is the principle of rendering the image and it should be so. With this parallel projections rendering, for FOV 180 degree the width will be infinity. All standart HMD used parallel projections - and it’s not good for big FOV HMD.
Below sample for left eye:

Beat Saber Update 3/14/2019 Parallel Projections still required to be enabled

This seems to be the case on the 8k as well.

(See my results based on IVRSystem::GetProjectionRaw here:


WTF?? Fix needed ASAPPPPPPP @PimaxUSA @Sean.Huang @Matthew.Xu @xunshu

Who else should I tag? Cause the ones I tag never seem to respond to me lol


should’nt it be ASSSSSSSAP? :wink:
i’m pretty sure they are aware of the performance problems with PP, its no news that it takes a lot of gpu resources needed elsewhere


Heh wow the Rift is just 87 degrees according to this test. It’s no secret we are constantly optimizing PP and that it requires extra processing power for it. This is mostly an issue that requires developer support and we have been reaching out to many of them with very good results.


Actually I think these images show why the extra vertical FOV is needed. It’s wasted on the inner parts, but needed for the outer corners. Look at the gray disks, the extra 12 degrees are needed to keep them inside the image.


you just dont see these corners in HMD, i ready to see less vertical fov in edges ( i think i just will not see difference)


While PP will always require more processing (especially for wide FoVs), and making non-PP work is a developer task, based on these findings it should be possible to make PP significantly more efficient at the driver level. Even if some of the FoV is needed in some locations, I’m sure the masking could be a lot more aggressive vertically in PP mode.

By the way, how do you get the backer tag? I’m a 8k KS backer.


Poke @Heliosurge


You are not alone :slight_smile: (Parallel projection = +32% of processed pixels?)


According to my rough calculation, lens length is about 77mm. Is this right?


How did you calculate it? Also do you talk about the lens or the panel?


Maybe Pimax could add a “fast PP” tickbox to pitool.

In this fast PP mode the rendered FOV would be the same than with PP mode off (but still making the correction for angled displays).

The result would be a final image with some black areas “but” with the exact same performance than with PP off.

When a game requires PP to be activated but real (full) PP is too demanding for your GPU, I would find better to be able to play this game with a non optimal image (black areas due to fast PP) rather than just not being able to play the game at all (or at best having to accept playing with too low fps).


you could just reduce fov (to small) or/and reduce the render res (pitool or steam vr)?
if its saved as profile in pitool then its not much extra work (it seems they are still working on profiles)


And if the game still renders with too low fps even at small fov ?

And for reducing render res, well, I may prefer having some black areas but with good resolution for the displayed content, than a 100% filled fov but with too pixelated content.


Lenses have 82 mmx 58 mm size.