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I'm currently working on a spaceship render. The engines glow and emit light. I have cubes behind each thruster that contain volumetric properties, I want these to look like a subtle back burner or just some ambient light coming out from the thrusters.

As you can imagine, the engine thrusters are circular. I have my volumetric in a cube, and of course the gas is cubic. It is not the right shape I am trying to accomplish. I need the volume circular, or just soften edges.

I have attached an image of the render, with the problem of the square volumetric occurring, as well as a screenshot of the nodes I used for the volumetric shader.

shaderspaceship

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3 Answers 3

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You could just consider the box to be a vector space in which you can sculpt your flame, by making its [ density | emission strength | color ] a function of the box's X,Y and Z.

Keeping it simple, here .. This box measures 2x2x4 Blender Units with its origin in the center of its base, and X,Y, and Z are measured in Object space.

enter image description here

  • (Left) By setting the density to 1 - the XYZ length, you get a hemisphere:

enter image description here

  • (Center) You could scale the Z to get an ellipsoid:

enter image description here

  • (Right) You could split the Z off as a multiplier, and sculpt it with a curve:

enter image description here

Of course you could extend this principle to vary colors, get flames-within-flames, etc. etc.

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  • $\begingroup$ ..oops, I left the file in Cycles.. but it works fine in EEVEE.. $\endgroup$
    – Robin Betts
    Commented Dec 11, 2020 at 10:35
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If you start with a UV sphere as your "volume object", you can constrain the volume using a (scaled & clamped) Spherical Gradient (Gradient Texture), as a Mix Factor between the Volume and a Transparent Shader.

Sphere

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    $\begingroup$ Why so complicated? There's no need for a Transparent Shader and a Mix Shader, this is no surface material.... just plug the output of the Color Ramp into the density of the Volume Scatter Node. Wherever it is black, the density is 0 (= transparent). If the density is too low or too high, put a Math Node set to Multiply between Color Ramp and Volume Scatter. Apart from that, the answer provided by Robin Betts works much better for your purposes because you don't have shape the bounding object for the engine shape. $\endgroup$ Commented Dec 11, 2020 at 11:31
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Just an idea I tried out for you really quickly. Didn't get great results, but didn't try long so you may be able to get it to work. If you:

  1. Make the volumetric shape emit particles (maybe creating some internal geometry so that it emits particles inside the object)
  2. Create a small sphere object that has the volumetric material
  3. Make the particle system emit this object.

Still gives kind of a pixelated look as all the little objects are still cube volumes, so may not work.

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