[3D] Z component of lines is discarded because of a buffer computation

[ptitjano]

What is the bug or the crash?

When displaying lines in a 3D view, the Z component of the lines is completely ignored and therefore they are stuck to the terrain even if altitude clamping is absolute or relative.

Here is a screenshot of a simple line rendered as a simple line. The altitude is correct:

The same line rendered without the "simple line" flag:

On the second screenshot, the Z component of the line is completely ignored.
This is because, a buffer of the input lines is computed during the preprocessing stage. This algorithm completely discards the Z component of the geometries:

QGIS/src/3d/symbols/qgsline3dsymbol_p.cpp

Line 146 in c63565d

QgsAbstractGeometry *buffered = engine.buffer( width / 2., nSegments, endCapStyle, joinStyle, mitreLimit ); // factory

Steps to reproduce the issue

1. Load a vector layer with lines
2. change the Z symbols of the layers and set altitude clamping to absolute or relative
3. create a new 3d view
4. line is displayed along the terrain even if its altitude is different from zero

Versions

3.35.0-Master

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

No response