Respect depth_shift with respect to z level in CairoMakie

[asinghvi17]

Description

Respects the depth_shift kwarg in CairoMakie 2d plots, currently purely as a subtractive factor so we can distinguish between plots at the same z-level.

This lets Tyler maps plot correctly (non-blurry) in CairoMakie.

Needs tests, I'll probably add a simple mockup of a Tyler.jl map via two image plots with different depth shifts. That is if this subtractive approach makes sense. I'm not sure if this is the most correct thing to do though...cc @ffreyer

Type of change

Delete options that do not apply:

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[MakieBot]

Benchmark Results

SHA: 3019288e6b626e116032d0666bba1d723b27fd95

Warning

These results are subject to substantial noise because GitHub's CI runs on shared machines that are not ideally suited for benchmarking.

[ffreyer]

Why not just translate instead?

[asinghvi17]

I think we were using depth shift to keep things general between 2d and 3d plots, where tiles at different z levels look pretty odd :D

Plus it's robust to transform_func where as in the 2D -> 3D case z translation may do strange things (since it translates after transform_func is applied)

[ffreyer]

I don't like depth_shift creeping into 2D rendering and this plot sorting thing. For 2D you should be able to do everything you want with just translate and plot order. For 3D CairoMakie is just not the right tool. There are some special/niche cases where plot order/depth_shift help, but it doesn't seem particularly useful to me to treat those. As a whole 3D is still not going to work without rasterization.

In terms of correctness, well, plot sorting in the first place isn't correct. It only looks at the z shift from translations and completely ignores the plot (i.e. z in plot args). Which is typically fine in 2D... For 3D neither of those have anything to do with depth anymore.

In 3D using just depth_shift would make more sense than using translations. At least that corresponds to depth, even if it ignores everything. Combining it with translations is mixing apples and oranges. The technically correct thing here would be sorting based on clip_pos[3] / clip_pos[4] + depth_shift per pixel, which isn't possible.

In 2D depth_shift and z translation act on the same axis but on different scales. You could bring them to the same scale with

z = zvalue2d(plot) # grabs plot.transformation.translation[][3] or equivalent atm
pv = scene.projectionview[]
depth = pv[3, 3] * z + pv[3, 4] + depth_shift

if I'm not mistaken. This might result in an opposite sign to what we have now. It should work correctly, but I still think it's redundant with translate.