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I have a particle system on a curved model. I want to have the particles only show up near the edges, at glancing angles. This means I have to have them only be created on faces with a glancing angle above a certain amount, or have them present but render as transparent. Using a texture to control their placement does not work because I need to be able to turn the model.

Is there any way to do this?

If I could use the emitter's normals in the particle's textures, that would be the most simple. But there doesn't seem to be a way to do that.

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    $\begingroup$ Please specify Cycles Render or Blender Render. Please show a explanatory image of the mesh. $\endgroup$ – atomicbezierslinger Feb 5 '16 at 8:24
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Cycles Render with Particles

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In the above image are numerous undesirable issues. Some might disappear with a little thought. Convex sphere works easily. Concave Box with visible inside and outside is more difficult. The simple cube can have difficult glancing angles. Surface Normal testing is not enough in the general case. Material Nodes.

Alternatives

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  • Compositing. Alpha Over Node. Transparent Background. Optional Render with Emission BSDF glowing particles. Composite Blur Node - Gaussian. Blurr bright glow colors. Dilate Node to increase blur size. Multiple layers composited if particles are used in final composition. Object ID or Material ID can be use to select desired pixels in the compositor. Stylized Blur.

  • Freestyle and Compositing.

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  • Volume Shading with Emission

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Below image. Quickly contrived Volume Shading. Meshes that Shrink/Fatten in a visually acceptable manner make this possible. Convex, Sphere, Torus Meshes.

enter image description here

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  • $\begingroup$ What are the actual node setups? I see that it is working, but I'm not clear on how it's being done. $\endgroup$ – Drudge Feb 8 '16 at 2:17

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