Question optimizing a multi mesh object (car) for performance

hi, i know its generally better to reduce the number of meshes in an object so there are less draw calls.

but in the case of my car, i have a body and 4 wheels. do you think its better to combine the whole lot into a single mesh? (i don't care about rotating the wheels BTW, its static), or is it better to keep each wheel a separate mesh since only 2 wheels will likely be visible at any given time, so save on rendered polys?

thanks

 

If it's a static background object with no moving part it should be a single mesh and one material. That'll be one draw call. Polycounts are clost to being irrelevant on modern computers, unless we're talking WebGL or mobile or perhaps low-end office PC with integrated graphics.

 

its not a single material, its about 6, and no easy way to make it one (they all have normals, height maps, etc), it would take forever to combine into one texture. its a PCVR game. does that make any difference to your answer? its not like i have a performance problem at the moment but i'm just getting started populating the scene

 

Just use SRP and you won't have to bother with draw calls or inefficient batching of BIRP. Have as many materials and meshes as you want.

 

I have no idea how to do that, way above my pay grade. i'll stick with URP for now but something to think about i guess. thanks

 

That's not how computer graphics work.

Every single poly is "rendered" if it is in the scene view and not otherwise culled.

Culling occurs for various reasons, but hiding behind a dynamic object like a car certainly isn't one of those reasons.

Even a poly facing away from the camera is technically "Rendered," inasmuch as some portion of the geometry pipeline must compute the dot product from the camera and decide it is facing away.

You should fire up the Frame Debugger (Window -> Analysis -> FrameDebugger) because it's kinda fun to see what is what as your scene is assembled. Let's you step-step-step through all the parts of it.

 

Just make sure SRP Batcher is active in your URP asset and use shaders made with Shader Graph or just default URP shaders, that's mostly it.

https://docs.unity3d.com/Manual/SRPBatcher.html

 

Some extra info on that, srp batcher can (mostly) batch different materials together if they have the same shader. That should be achievable for most of the objects

 

thanks i will because i notice i'm getting over a thousand draw calls even when i'm not really facing that much

 

sorry i'm confused with the docs, it says
Using the SRP Batcher in URP
To activate the SRP Batcher in URP:

1. In the Project window
   , select the URP Asset.
2. In the Inspector for the URP asset, enable SRP Batcher. If this option is not visible, follow the instructions below.

How to show Additional Properties for the URP Asset
Unity doesn’t show certain advanced properties in the URP Asset by default. To see all available properties:

• In the URP Asset, in any section, click the vertical ellipsis icon (⋮) and select Show Additional Properties.

is it talking about this

because i don't see the show additional properties thing

 

No, wrong asset. You're looking at the global settings (that's featured in the next section of the docs). You want the actual render pipeline settings, with is assigned in the Render Pipeline section of the Project Settings. If you haven't created one, there's a link in that page on how to make one.

 

thanks, it looks like i have SRP batcher enabled all along

my performance is quite good really, 70fps (limited by virtual desktop link to VR headset ) for a RTX 3060 laptop

 

Few things:
1. Disable SSAO. This kills performance, especially for VR
2. Disable HDR, no VR set uses it atm
3. Lighting and shadows can impact performance quite a bit
4. For mobile 1.6mil tris is very high, for desktop vr it's fine

 

Just make sure you have a small amount of SRP batches in this list and how many drawcalls are inside one batch probably doesn't matter. You should probably focus on GPU optimization, primarily fillrate - avoiding microtriangles and transparency overdraw. Use GPU profiler tab in profiler.

 

i just "discovered" occlusion culling (kind of like how Columbus discovered America) and now i'm down to about 400 draw calls, which still seems high, but manageable