Grid object

[almarklein]

Addresses one point in #739.

Techniques

I'm looking (until now) at two approaches:

• The "Nico-grid" from Nicolas Rougier's paper.
• The Prestine-grid from this post by Ben Golus and this shadertoy.

I'm comparing these and will likely combine the best of both ... wip.

Notes

• Grid range:
  • Sometimes you want a grid with a specific range. Sometimes infinite.
  • This is more a matter of doing the right tricks in the vertex shader. Does not (really) matter for the grid-drawing.
• Line width:
  • Can be in screen coords, world coords.
  • The Prestine grid mimics a texture grid, and is in world coords, but flat in the plane (not bill-boarded).
  • Can probably take code from line rendering to make it do whatever we want.
• Major and minor ticks:
  • Must be done in one shader; drawing two grids does not blend well.
  • The Nico-grid does this. Can probably make this work for Prestine grid.
• Performance:
  • Do a small benchmark to see if one is significantly slower.
• AA:
  • super in both.
• Distance fading and suppression of Moiré artifacts:
  • Very good in the Prestine-grid. Not sure yet for the Nico-grid.

Use-cases / scope

Focusing on grids for axes in this PR. Will also consider log, polar and map projections, to at least know how it will fit in.

Other use-cases (for later):

• Draw a surface (height map) and have planar grid lines or isosurface lines drawn on top.
• Draw gridlines over a mesh, the texcoords specify the grid space. Maybe a MeshGridMaterial.
• Render checkerboard instead of a grid.

---

Early result of the prestine grid:

[Korijn]

• Major and minor ticks:

  • Must be done in one shader; drawing two grids does not blend well.
  • The Nico-grid does this. Can probably make this work for Prestine grid.

The prestine grid has this feature all the way at the bottom of the article, including a link to shader source:

[almarklein]

Also easy to make prestine grid use screen-space line width.

[kushalkolar]

That is indeed a very nice grid with minimal moire 😮

[almarklein]

Almost done! Only Cartesian grids for now. Want to look at log/polar/maps later.

One remaining problem is that the inf grid looks rather odd on LavaPipe ... 🤔

[Korijn]

Is the default orientation the same as a plane geometry? :)

[almarklein]

Is the default orientation the same as a plane geometry? :)

No, it's not. The default plane orientation is xy. I opted for a default xz because that way it can function as a floor in most our examples. I can change the default to match xy. We can force the user to specify the orientation, leaving less room for surprises.

[Korijn]

Something that stands out to me is that the infinite grid does not actually reach out to the horizon :) I think I can see its borders and a corner

[kushalkolar]

Something that stands out to me is that the infinite grid does not actually reach out to the horizon :) I think I can see its borders and a corner

I was wondering this too, is it the camera clipping planes along depth?

[almarklein]

the infinite grid does not actually reach out to the horizon :)

That's because it's not actually infinite, but scaled and positioned to appear infinite. If I scale the grid too much, the grid coords become unstable. But I'll have a look to see if I can crack it up a bit.

[Korijn]

So how does the prestine grid shader article achieve this effect then?

[almarklein]

Updates:

• The horizon is much better now. The vertex shader now creates a square consisting of a small inner quad and a (much) larger outer region. That way we have accuracy nearby, and massive range for a proper horizon.
• Changed the grid's orientation to be in xy-plane if its not rotated. The orientation argument is mandatory.
• The glitched screenshot I posted earlier applied to Vulkan (not just Lavapipe). It was due to how the uv for axis-lines was clamped, Fixed.
• Also saw how the grid looked bad for large step sizes. Turned out the math was not correct. Fixed that too.

[almarklein]

Ready from my end.

[kushalkolar]

Just played with it, it works really well! 🥳

[almarklein]

Yeah, I'm really happy with the end result. The prestine grid is amazing! And mixing it with a few ideas from Nicolas (most notable handling edges of non-finite grids) makes it more generally useful.

[kushalkolar]

10 million points and zooming along the grid 😆

https://www.youtube.com/watch?v=7pv0zurv7x0