Improve stratified sample strategy

[gkjohnson]

Related to #527, #449

There should be some way to de-correlate samples a bit more since at the moment all samples across the image are sampling from the same stratum with a common x and y offset. This results in highly correlated samples that expose the sampling patterns of shapes. This results in some swirling patterns especially when any spherical sampling is done. The shuffling approach could possibly also use some improvement.

Thoughts:

• Possibly reshuffling the strata more intelligently would help which requires understand generation step more.
• It's possible that we won't have a good image until all stratum have been sampled
• Possibly using a 4 color blue noise seed this can be helped
• Use a 3d texture with X: full strata for one sample, Y: new strata per id, Z: new strata per bounce

[gkjohnson]

The core issue is that we only have a single blue noise value which is used to offset both a X and Y across the strata so it's correlated between both axes. Using an offset that's spread well across both X and Y (and Z if possible) would be best. Perhaps some kind of 2d blue noise point pattern. The blue noise pattern could be reshuffled into a 2d point based on intensity value across the image

[gkjohnson]

Using the blue noise texture to derive evenly space points seems to not produce a smooth result. Possibly worth making sure the points are actually evenly spaced? Or maybe using another poisson or halton sequence numbers or another approach.

Before	After

Point generation

	this.image.data = new Float32Array( ( size ** 2 ) * 2 );
	this.format = RGFormat;

	const result = generator.generate();
	const bin = result.data;
	const maxValue = result.maxValue;

	const newData = this.image.data;
	for ( let i = 0; i < maxValue; i ++ ) {

		const index = bin.indexOf( i );
		const x = index % size;
		const y = Math.floor( index / size );
		newData[ 2 * i + 0 ] = x / size;
		newData[ 2 * i + 1 ] = y / size;

	}
``

[gkjohnson]

Some other noise approaches to use:

https://developer.nvidia.com/blog/rendering-in-real-time-with-spatiotemporal-blue-noise-textures-part-1/