Bridge Edge Loops: Unpredictable Curvature and Lack of Directional Control on Zero-Angle (Parallel) Faces

When using the Bridge Edge Loops tool between two perfectly parallel or co-planar edge loops, the resulting curvature direction is highly unpredictable and non-repeatable, making precise modeling difficult for common structures like arches and handles.

1. The Observed Phenomenon (不可预测的行为)

I have created two identical pairs of edge loops:

Initial Group (Labeled '1' in the image): When bridging the first loop pair, the resulting connection shows an S-shaped (or double-bend) curvature.

Copied Group (Labeled '2' in the image): When bridging the second loop pair (a direct copy of Group 1), the resulting connection unexpectedly shows a normal N-shaped (single-bend/concave) curvature.

This inconsistent behavior persists regardless of:

Face Orientation: The results are the same whether both faces are correctly oriented (Blue/Outward) or flipped.

Active Selection: The selection order of the vertices/edges does not reliably dictate the outcome.

The different, non-deterministic result for identical input geometry suggests that the algorithm is defaulting to internal, unstable data (like Vertex ID order) when robust geometric guidance (like a non-zero angle) is absent.

2. The Problem with the Current Solution (当前方法的局限性)

This ambiguity makes the tool unreliable in common modeling scenarios where precise and consistent curvature is required between parallel surfaces.

3. Proposed Solution for Control (建议的解决方案：基于法线控制)

To solve this inherent instability, I propose introducing a secondary factor based on Face Normal Consistency to control the transition direction when the angle is 0 。

Proposal: Implement an option that uses the relationship between the two edge loops' Face Normals to define the curvature sign (S-shape vs. N-shape).

Normal State (User Intention) Proposed Resulting Curvature Consistent Normals (Both Blue/Outward) Forced N-Shape (Convex/Arch) transition. Conflicting Normals (One Blue, One Red/Flipped) Forced S-Shape (Double-Bend) transition.

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This would provide the user with clear, predictable control over the final transition shape simply by using the native Flip Normal tool (Alt + N) to indicate the desired curvature. edited Gemini AI.