Enable "auto" logarithmicDepthBuffer only when EXT_frag_depth supported

Issue: some devices exhibit artifacts with logarithmicDepthBuffer = true on the scene renderer when WebGL extension EXT_frag_depth is not supported by the device.

Impact: undesired artifacts, especially for objects close to the camera

Instead: if scene renderer attribute logarithmicDepthBuffer = auto, set this renderer setting logarithmicDepthBuffer true only if EXT_frag_depth extension is supported.

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Psuedo code suggestion, starting here: https://github.com/aframevr/aframe/blob/67d568c263173ef0a56efc1e0d9e08a6f2d2d2a8/src/core/scene/a-scene.js#L609

// Existing logic
if (rendererAttr.logarithmicDepthBuffer && rendererAttr.logarithmicDepthBuffer !== 'auto') {
  rendererConfig.logarithmicDepthBuffer = rendererAttr.logarithmicDepthBuffer === 'true';
}

// Additional logic
if (rendererAttr.logarithmicDepthBuffer == 'auto' && renderer.extensions.get('EXT_frag_depth') !== null) {
  rendererConfig.logarithmicDepthBuffer = rendererAttr.logarithmicDepthBuffer === 'true';
}

[jbaicoianu]

One trick I’ve had success with in the past using regular depth buffer is to dynamically update your near/far parameters based on the contents of the scene, and their distance to the player. Normally the type of z-fighting you’re dealing with in your scene is only visible when you zoom out, in which case the default near parameter is unnecessarily small. The closest object to the camera may be 10s or 100s of meters away so precision of 1cm isn’t necessary.

[kfarr]

I suppose you’re right, this “magic” auto behavior really isn’t that useful for general cases.

So really what I proposed is more of a short-term hack and shouldn’t be promoted behavior in A-Frame. Best to close this then and look for better solution