Polymesh objects can be rendered as volumes. This gives many creative opportunities for rendering solid objects in varied and interesting ways. This short 'making of' tutorial shows how to combine a polymesh with a volume by combining their shading using the displacement attribute of a standard_volume shader. We will also cover how to reproduce the above-animated effect using the cell_noise, color_correct, ramp_rgb and range shaders connected to volume_displacement of the standard_volume shader. An example of a free to use head scan model can be found here.
The polymesh should be closed and not have anything self-intersecting, otherwise, the volume may not render correctly.
Step Size
- First of all, we need to convert the head mesh to a volume. Select the mesh and under its Arnold attributes, increase the Step Size to 0.1. When the Step Size is positive, it turns a polymesh into a volume and its value is used as the base step for raymarching the volume.
More information about volume step_size can be found here.
Standard Volume
- Assign a standard_volume shader to the polymesh and increase the density to a very high value of around 4000. This will ensure that the displacement texturing looks more defined later.
Head mesh rendered as volume
Range
- Connect a range shader to the volume_displacement of the standard_volume shader.
- Increase its output_max value to around 30. This will increase the effect of the volume_displacement once we connect the cell_noise shader to it.
Camera Projection
To animate the effect from top to bottom we will project a ramp through the V direction.
Create a camera_projection shader and connect it to the input of the range shader.
Remember to select the render camera that you want to use for the camera_projection.
Ramp RGB
- Create a ramp_rgb shader and connect it to the projection_color of the camera_projection shader.
Color Correct
- Connect a color_correct shader and connect it to the input of the ramp_rgb shader. You can use this to fine-tune the cell_noise shading effect.
Cell Noise
- Create a cell_noise shader.
- Change the pattern to cell1.
- Disable additive.
- Ensure that the coord_space is set to object.
- You will need to adjust the scale according to your scene size. In this case, the cell_noise is thinner because Y and Z are less than X.
- Increase the density to 1 and set randomness to around 0.2 to add some irregular shapes.
Final cell_noise settings
Animation
- Keyframe the black color of the ramp_rgb from left to right over time to see the effect move bottom to top across the head volume.
- Keyframe the time attribute of the cell_noise shader to animate the cell_noise effect.
Conclusion
That's it. Remember to increase the volume_samples for any lights in the scene when rendering the final animation.
Further example with cell_noise scaled in Y