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It is possible to render CINEMA 4D spline curves with Arnold. An Arnold tag has to be added to a CINEMA 4D spline object, which allows you to define Arnold specific settings, e.g. curve width and the sample rate used to describe the spline. Shaders can be added to the Spline object just like to any other object; default is a standard_hair shader.


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Arnold Parameters added to a spline via the C4DtoA tags menu

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Info

The use of SSS is not supported with point and spline primitives and is therefore not recommended.

Render

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Curve Width 

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The curve width can be modified using the scale attribute if you extend the UI (small black arrow on the left of the parameter name). By Linear interpolation the spline points are exported with a linear basis. Other interpolation methods take samples from the spline and use a catmull-rom basis in the Arnold curves node.  With this approach, any C4D interpolation types and closed curves can be matched.

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The curve width can be defined along the spline with a spline custom GUI. The user can define the radius width and can scale value with the spline control.

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Determines whether or not the curve will render.


Thickness 

Defines the rendered thickness of the curve.

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Thickness 0.01 - 0.1

Thickness Spline

Thickness can be modified via a spline along the curve, which acts as a multiplier over the base Thickness. 

Thickness Texture

It is also possible to connect a texture map or shader (e.g. Noise) to control the curve width. The shader is evaluated along the U coordinate (V=0). U=0 is the start and U=1 is the end of the spline.

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Thickness modified by a Noise texture


Note

Only C4D shaders are allowed, no Arnold shader networks can be used.

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curves

Samples

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Curves

Min. Pixel Width

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Export IDs

Export the index of each curve to the curve_id user parameter.


Motion Blur

Enable

Enable/disable motion blur of the spline.