float inaccuracy with low near clip plane, even when far clipping plane is low!

[pojoih1]

This is not a real Unity 5 problem but I thought you can finally touch this issue, especcialy with all the VR games out there that would benefit:

I’m using a multicamera setup to display the inside of a cockpit and having troubles to make it judder- and flicker-free. Even with camera clipping plane values from 0.1 - 3m I get shadow flickering and float inaccuracy. When I pull up the near clip plane the flickering gets lower until it vanishes completly at 1m.
The funny thing is I don’t get any problems with clipping planes 1 - 100 OR 1 - 100000000! It’s just a problem with values unter 1m. I thought the Z-Buffer is adjusting to the clipping planes? So 0,1 - 1m should be less flickery then 1 - 1000m?

Any change to get around this?

[Devil_Inside]

The first link I got in Google: OpenGL FAQ / 12 The Depth Buffer

You may have configured your zNear and zFar clipping planes in a way that severely limits your depth buffer precision. Generally, this is caused by a zNear clipping plane value that’s too close to 0.0. As the zNear clipping plane is set increasingly closer to 0.0, the effective precision of the depth buffer decreases dramatically. Moving the zFar clipping plane further away from the eye always has a negative impact on depth buffer precision, but it’s not one as dramatic as moving the zNearclipping plane.

The OpenGL Reference Manual description for glFrustum() relates depth precision to the zNearand zFar clipping planes by saying that roughly log2(zFar/zNear) bits of precision are lost. Clearly, as zNear approaches zero, this equation approaches infinity.

While the blue book description is good at pointing out the relationship, it’s somewhat inaccurate. As the ratio (zFar/zNear) increases, less precision is available near the back of the depth buffer and more precision is available close to the front of the depth buffer. So primitives are more likely to interact in Z if they are further from the viewer.

[pojoih1]

Thanks a lot. Haven’t thought of a general limitation, I just googled unity-specific stuff.
Seems I have to live with it

[Devil_Inside]

I don’t know what you mean by multicamera setup, but you can try making 2 cameras, one will render just the cockpit, the other one will render everything else. This way you can set near/far clipping planes separately for each camera.

[pojoih1]

I’ve figured it out now. I wasn’t the clippingplane alone, I’m also too far away from the midpoint.
I’m currently fiddling around with a floatingOrigin but there are obviously some issues with particlesystem and occlusion culling.
Anyway this one is fixed. Thanks for the fast response and the explanation!

[Jaimi]

As you’ve discovered, the zbuffer is not linear. You have to push out the near clip plane as far as you can to gain resolution. Changing the far plane has little to no effect.