Makie - drawing lines through transparent surface

Specific Domains Visualization
1

Hi, I’ve been using Julia and the Plots package for a while, but only recently have tried using Makie for some visualizations, and ran into some problems. No matter what I try, I can’t get line segments to play nicely with transparent surfaces or with volumes.

As an MWE, if I make a simple surface and put line segments above and below it, I get what I would expect

using Makie
scene = Scene()

y = collect(-10:0.1:10)
x = y
z = zeros(length(x), length(y))

height = 5.0
x0 = 0.0
y0 = 0.0
z0 = 0.0
origin = Point3f0(x0, y0, height)
crosspt = Point3f0(x0, y0, z0)
finalpt = Point3f0(x0-2 ,y0+2, -height)
line1 = [origin, crosspt]
line2 = [crosspt, finalpt]
linesegments!(scene, line1,  linewidth=5, color=:red,)
linesegments!(scene, line2,  linewidth=5, color=:red,)
surface!(scene, x, y, z,  shading=false)

But if I change the last line to make the surface partially transparent as

surface!(scene, x, y, z, alpha=0.95, transparency=true, shading=false)

it draws the line as if the surface was completely transparent.

surf_transparent
surf_transparent876×545 60.6 KB

I have tried several variations of this (including changing the plotting order). Searching the forums I saw it suggested that alpha didn’t work correctly, so I attempted replacing the surface with meshes using explicit colors,

mesh!(scene, [-10,-10,10], [-10, 10, -10], [0,0,0], color=(:purple, 0.95), transparency=true, shading=false)
mesh!(scene, [-10,10, 10], [10, -10, 10], [0,0,0], color=(:purple, 0.95), transparency=true, shading=false)

but I get the same result.

Looking closely it seems the lines from the axis/grid also get drawn over the surface. Am I missing something about how transparency is supposed to work, or does it fundamentally not work with lines in Makie?

I am hoping someone in the community has some idea whats going on here. Thanks in advance.

2

This is an annoying problem…As if transparency isn’t hard enough already, I have two render targets for drawing primitives that need anti-aliasing (aa) and one that doesn’t…Lines don’t need aa, a.k.a fxaa (which is the algorithm i implemented), but a surface has fxaa enabled.
You can try this, to get better results:

using Makie
scene = Scene(camera = cam3d!)

y = collect(-10:0.1:10)
x = y
z = zeros(length(x), length(y))

height = 5.0
x0 = 0.0
y0 = 0.0
z0 = 0.0
origin = Point3f0(x0, y0, height)
crosspt = Point3f0(x0, y0, z0)
finalpt = Point3f0(x0-2 ,y0+2, -height)
line1 = [origin, crosspt]
line2 = [crosspt, finalpt]
linesegments!(scene, line1,  linewidth=5, color = :red, fxaa = true)
linesegments!(scene, line2,  linewidth=5, color = :red, fxaa = true)
surface!(scene, x, y, z, shading = false, colormap = [(:blue, 0.5), (:green, 0.5)], fxaa = true, transparency = true)
3

Thanks for the quick reply, this fixed the issue. There are some artifacts when a few bunched lines overlap, but it is minor. This also fixed a related issue I had where lines wouldn’t go through volumes.

If you don’t mind a related question, I am trying to figure out how to changes colors on volumes with absorption. In the example at

https://simondanisch.github.io/ReferenceImages/gallery//3d_cube_with_sphere_cutout,_outside/index.html

it seems the matrix adjusts the amount of red (first element in rgba). Because it uses algorithm = :absorptionrgba I am inferring that you could change all of the rgba channels, but I can’t figure out how. I’ve tried making the matrix elements tuples, RGBA objects, and passing one array for each channel, but not luck. Any suggestion is appreciated, thanks!

4

absorptionrgba will look up the color value from a colormap…
So you’ll need to supply colormap = vector_of_colors/symbol/... :wink:

5

First, thanks for all of the work on Makie, it is great to have this in Julia.

Even specifying a colormap I haven’t been able to get the volume to change color using absorptionrgba. However, this did work for indexedabsorption, so I think I am good to go. Thanks again for all of the help.

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