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What are the Performance-killer for VR(eg.OculusQuest2)? all postprocess, all screen-space?

what are the Performance-killer for VR(eg.OculusQuest2)? all postprocess, all screen-space? all works on the full-screen RenderTarget?
so,
SSAO, SSR, SSDO, etc…
Fog, Depth of Field, Bloom, MotionBlur, Tonemapping, ColorGrading, Auto Exposure, Channel Mixer, Chromatic Aberration, Grain, Lens Distortion, Panini Projection, Vignette, White Balance, etc…
pre-z ?
detailMap?
the light and shadow…is the Default ForwardRender in UE4.26/27 use Clustered ForwardRender?
only 1 DirLight, as less light(esp. DynamicLight) as possible?
bake all the Shadow except the Characters(use dynamic shadow)?
Pre-caculate for lighting and shadow, such as IBL?

how about PBR? and how to make it the most similar to a state of art PBR game on PC?
eg. how to make effcts most similar to Bloom? to AO(the old way that let artists draw on the texture)?

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Box/SphereReflectionCapture is also not allowed to use in VR?
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how about the GPU instacing in VR? what if plant grass and trees?
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as SSR is not able to be used, so it’ll very difficult to have Water? including water spot, puddle, river, sea?
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anything related to LightMass should not be used, eg. LightMassImportanceVolume ?
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DisplacementMap in VR?
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paticle system in VR?
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for Quest2, the count of Material is better NOT to lager than?
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should forbid Translucency material in VR? hit perf very much? is there efficient way if want Translucent effect?
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Tanslucent UI also cost much and should forbid to use in VR?
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what’s the preferred setting values for ‘Build’ lightmap for Quest2? Take test and the smaller resolution the better?

Thanks!

Here we gooooo!

  • The first thing you want to do is dig into Project Settings and (i just click ‘All Settings’ and use the search bar) find ‘Forward Renderer’. You want to enable Forward Shading and Vertex Fogging for Opaque, but the big one you should enable is Forward Shading. This changes the engine’s renderer to a ‘forward’ rendering method instead of a ‘deferred’ rendering method where (and this is a massively simplified explanation) it renders fewer buffers faster and pushes the frame once it’s done, rather than waiting for all the render buffers to be calculated before assembling the frame and pushing it to the displays. You won’t be able to access a few buffers like Scene Depth, but you’ll see somewhere around a 20% performance increase.

  • Next, hit up Engine>Rendering>Mobile and enable Disable Vertex Fogging (tick the box, this is phrased oddly), set the max number of CSM Cascades to 2 or 1, set Mobile MSAA to 4x or lower (use your best judgement in testing) and enable Use Legacy Shading Model. None of this will kneecap your visual quality, but will improve performance at least a bit, and will be handy if you deploy to Quest/2 as a standalone package.

  • Enable Occlusion Culling and Round Robin Occlusion Culling. Occlusion culling will stop oobjects and meshes from being rendered if theyre not visible to the player, and Round Robin Occlusion Culling means that in VR, this occlusion testing is done in one eye at a time, which lowers a bit more overhead.

  • In Engine>Rendering>Default Settings, disable Bloom, Ambient Occlusion, Motion Blur and Lens Flares. Each of these is an additional render pass, and expensive, so disable for more performance boosts. Ill get to materials in a bit, but ill note here that you can create materials in such a way that objects will generate AO as baked, static lighting which is a handy alternative to real-time AO. While we’re here, set Anti-Aliasing Method to MSAA; its the best tradeoff between performance and visual fidelity.

  • In Engine>Rendering>VR, disable Mobile HDR and enable Instanced Stereo. This is also where RR Occlusion Queries is, for reference. I haven’t tested performance with Mobile Multi-View enabled, but this may reduce some overhead in standalone Quest/2 projects. It’s the instanced stereo option that’s critical to enable, as this will instance draw calls per-eye, which should give you a performance boost of around 30-45%.

  • In your level’s World Settings, find an option under VR called Mono Culling Distance. This is the distance from the camera at which the engine stops rendering in stereoscopic and will only render in monoscopic. This means that beyond a certain distance, the engine only needs to render everything once and pipe it to both eyes, which is ideal for background assets. By default this is disabled (set to 0.0) but start with like 500 and see how it looks.

  • Practices. Try to avoid using post-processing, as this means an additional render pass, but if this is unavoidable, at least try to use a naked PP volume without any PP materials. Don’t use dynamic lighting if you can avoid it; dynamic lights are a disaster for performance in the best of circumstances, so get used to wrangling lighting builds. Don’t use fog. Don’t use translucency (or at least as little as possible) and avoid complex materials with lots of instructions.

  • There’s an adage in VR development that states “Code like its 1999”, and it rings true. You want to be using simple materials, optimized meshes, static lighting, and minimal complex calculations such as physics. LOD aggressively. I’ll repeat, LOD AGGRESSIVELY. You can either import your own LOD meshes for props or let the engine generate them for you, but either way the most meaningful way to reduce quad overdraw and therefore per-frame processing time is to use LODs.

  • Materials. As I mentioned, just avoid translucency if possible. Masked materials (with dithered translucency) are better, but ideally you just want to not use translucent or masked materials. You can add static AO to your materials, and after a lighting build, you can manipulate that AO like any other texture mask. Speaking off, mathematical calculations require way less memory than texture lookups, so if you can, either pack your textures or try to use colors and simple greyscale pngs. Furthermore, you should create a single master material for all your textured objects and use instances to shade your scene - this is a huge way to reduce GPU overhead, due to the engine only needing to reference one material, instead of a different material for each object. Lastly, there’s an option in the material settings called ‘Fully Rough’ which basically forces a roughness of 1 and saves a heap of material instructions. You can use fresnel nodes and normal maps to get some kind of shine back on surfaces. Beware normal maps, however, because in some cases they can display differently in each eye.

Apologies for the long essay! This is by no means exhaustive and Im sure others here will have more notes, but this should get you started :slight_smile:

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Thanks so so so much! :smiley: The longer, the better!

Post processing effects are also heavily dependent on whether you’re using the standard Mobile HDR (which is more expensive but more robust) or disabling it to rely on the Quest-specific tone mapping and whatnot.

I don’t think the screen-space processes are available with the Forward Renderer, so those are out. Motion blur is risky because it has the potential to be a less comfortable effect, particularly if there’s lag which the blurring itself might cause. Bloom is a medium expense, probably to be used in small doses if it’s needed. Color grading and LUTs have been very cheap so far.

All good notes :slight_smile: Use Motion Blur in VR at your own risk, theres a high probability it will make you puke and (if it works at all) might be identified by the player as ghosting, which is also not ideal.

In very aggressively optimized scenes (think original DOOM quality) I’ve used bloom and SSAO and just eaten the performance hit because it wasn’t enough to blow my frame budget. It’s all a big balancing act between your minimum target hardware and scene complexity, so beyond general advice on this topic its a judgement call.

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while Mobile HDR is on, many projects i tested is all black while launch on Quest2…donot know why, but i always turn off it first…and i think many tutotial suggest this off.

so it’s better to turn MobileHDR off, and use Quest-specific tone mapping? where should i set this?
(just update the content on the top, please take a look, thanks:D)

how about Quest2, and FPS
(just update the content on the top, please take a look, thanks:D)

not quite understand here. would you please send me some demo or tutorial? thanks

RR = ?

so no fog in VR, or is there method to replace it?

‘enable Vertex Fogging for Opaque’?
‘enable Disable Vertex Fogging (tick the box, this is phrased oddly)’?

eg. how to deal with the Characters’ shadows? just remove them seems not good to look…

lol, 1999, after Doom, Quake release, and maybe years CS was popular? :smiley:

eg. for FPS, is there any recommanded rules for Character, Gun, building, etc, to give a range of Vertex/Triangle count for the artist?

in Multiplayer game, is IK comsuming? if use IK not only for feet/leg butalso for hand/arm/head/upperbody, will it possible?

means use MAX count for LOD level. and reduce the triangle count rapidly as the LOD increase?

would you please give me a turotial or demo? thanks!

use PNG while dev, and pack all these PNGs to big PNGs with the size of power-2 such as 10241024 or 20482048 while shiping/release the formal game?

so save GPU/video memory is one side, and how about their speed?
and speaking off, take Quest2 for example, while need to choose between FPS and video-memory& RAM-memory(not sure about the memory it use, will check later), normally still have to take care of the memory first, or use tools to check and profile first, then make a decision?