Performance Issues when canvas (with child) is attached to main camera

I've seen a huge performance impact, when I attach a canvas which has a child (text, panel, image) to the main camera.

Profiler shows this all the time:


This was done in a simple empty (VR) application with unity 2018.4.3f1.



When I remove the image from the canvas, I get a huge performance boost and the Canvas.BuildBatch-calls are gone.
I wanted to use the image as a crosshair as showed in many tutorials. But with such a big performance hit, it does not make sense.

Any way to optimize this? Why all the calls permanently? The canvas is not changed at all, just the position is updated? Or am I missing something?

 

Update: It's the same in unity 2019.2.
You can see in profiler what happens, once the image is switched on:

 

And another update. It seems only an issue with VR. When I disable VR and just move the camera in the game, I don't see this stuff in profiler and don't see the performance impact when adding the image:

 

I'm in the exact same situation here. The Unity VR Samples uses this method (canvas is child of main cam).

 

If your case is really just a cross hair, don't use a canvas, just use a simple sprite renderer parented to your camera rig.

 

I found the same problem. It occurs when you are in VR, and do anything to move, resize, or enable a canvas. Here is the bug for unity:
https://issuetracker.unity3d.com/is...-a-child-is-attached-to-the-main-camera-in-vr
If you want this fixed, go there and up vote it.

 

ugui sucks, I can easily write a ui system better than unity
I decide to use quad&textmesh instead of ugui