# Makie - drawing lines through transparent surface

**URL:** <https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148>\
**Category:** Visualization\
**Tags:** question\
**Created:** [August 29, 2019, 2:08am UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148 "2019-08-29T02:08:31Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![nhardy](https://avatars.discourse-cdn.com/v4/letter/n/9fc348/32.png) [@nhardy](https://discourse.julialang.org/u/nhardy)\
**Post date:** [August 29, 2019, 2:08am UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148/1 "2019-08-29T02:08:31Z")

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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

```julia
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

```julia
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](https://global.discourse-cdn.com/julialang/original/3X/4/5/45d0400174028351f65112ca9906e64026326d79.png)

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,

```julia
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.

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<div class="post-metadata">

**Author:** ![sdanisch](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sdanisch/32/1406_2.png) [@sdanisch](https://discourse.julialang.org/u/sdanisch)\
**Post date:** [August 29, 2019, 8:23am UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148/2 "2019-08-29T08:23:55Z")

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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:

```julia
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)

```

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<div class="post-metadata">

**Author:** ![nhardy](https://avatars.discourse-cdn.com/v4/letter/n/9fc348/32.png) [@nhardy](https://discourse.julialang.org/u/nhardy)\
**Post date:** [August 29, 2019, 1:29pm UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148/3 "2019-08-29T13:29:32Z")

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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](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!

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<div class="post-metadata">

**Author:** ![sdanisch](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sdanisch/32/1406_2.png) [@sdanisch](https://discourse.julialang.org/u/sdanisch)\
**Post date:** [August 29, 2019, 1:51pm UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148/4 "2019-08-29T13:51:01Z")

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

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<div class="post-metadata">

**Author:** ![nhardy](https://avatars.discourse-cdn.com/v4/letter/n/9fc348/32.png) [@nhardy](https://discourse.julialang.org/u/nhardy)\
**Post date:** [August 29, 2019, 3:10pm UTC](https://discourse.julialang.org/t/makie-drawing-lines-through-transparent-surface/28148/5 "2019-08-29T15:10:28Z")

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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.