Struggling to understand curve extrusion

Question

What I am experiencing a lot in blender is invalid curve extrusion size. It works just fine for non-scaled curved but it gets messy once curve is actually scaled.

Steps to replicate...

1. Create a curve
2. Scale it up (required - lets go with 10x)
3. Extrude 1 m. Actual extrusion is 10m (that's expected)
4. Apply scale
5. Extrude param is still 1m but the actual extrusion is 10.

It just doesn't add up. Shouldn't extruded curve be actually extruded to the defined size? I think it's a bug but perhaps I am just missing something.

Shouldn't extruded curve be actually extruded to the defined size? I think it's a bug but perhaps I am just missing something.

Answer 1

Many of the curve object's features come from values which are defined at each Control Point.

This is very handy to benefit from the full potential of curves.

For instance, the Extrusion and the bevel Depth parameters are direct multipliers to the each control point's Radius parameter.

When you apply the curve's scale, you apply the visual transform, so its geometry should logically stay the same if all other parameters stay the same.

To do so, the curve's CP's radius parameters are all individually multiplied by the applied ratio. When you apply a scale of 10, the CP's radius are multiplied by 10 to keep the same visual geometry.

If you don't want this behaviour, click in the lower left corner to expand the operator properties, or press F9 and uncheck Apply Properties.

Once you do this, this behaviour will be executed every consecutive time you apply the scale until you restart blender.