egametang/ET · warning · Exception

rcBuildContours: Bad outline for region {i}, contour simplif

Error message

rcBuildContours: Bad outline for region {i}, contour simplification is likely too aggressive.

What it means

Thrown in rcBuildContours when a region has holes (nholes > 0) but its outline is null. With no enclosing outline, holes cannot be merged. The comment in source explains this happens when contour simplification settings are too aggressive, causing a region's outline to become self-overlapping and disappear.

Source

Thrown at Packages/cn.etetet.recast/Scripts/Core/Share/Recast/RecastContour.cs:953

                    }

                    // Finally merge each regions holes into the outline.
                    for (int i = 0; i < nregions; i++)
                    {
                        RcContourRegion reg = regions[i];
                        if (reg.nholes == 0)
                            continue;

                        if (reg.outline != null)
                        {
                            MergeRegionHoles(ctx, reg);
                        }
                        else
                        {
                            // The region does not have an outline.
                            // This can happen if the contour becaomes selfoverlapping because of
                            // too aggressive simplification settings.
                            throw new Exception("rcBuildContours: Bad outline for region " + i
                                                                                           + ", contour simplification is likely too aggressive.");
                        }
                    }
                }
            }

            return cset;
        }
    }
}

View on GitHub (pinned to 5cab01f7a8)

Solutions

Lower maxSimplificationError to preserve outline fidelity.
Reduce maxEdgeLength so outline edges are not over-merged.
Raise minRegionArea to eliminate tiny hole-bearing regions.
Switch region partitioning strategy if the geometry persistently produces bad outlines.

Example fix

// before
cfg.maxSimplificationError = 2.5f;
cfg.maxEdgeLength = 200;

// after
cfg.maxSimplificationError = 1.1f;
cfg.maxEdgeLength = 20;

Defensive patterns

Strategy: validation

Validate before calling

if (cfg.maxSimplificationError > 2.0f) Debug.LogWarning("Aggressive simplification may erase outlines leaving holes");
if (cfg.maxEdgeLength > 100) Debug.LogWarning("Large maxEdgeLength may collapse outlines");

Try / catch

try { var cset = RecastContour.BuildContours(ctx, chf, maxError, maxEdge, buildFlags); }
catch (Exception e) when (e.Message.Contains("Bad outline"))
{ /* lower maxSimplificationError / maxEdgeLength, retry */ }

Prevention

Keep maxSimplificationError modest (< 1.5) for complex geometry.
Limit maxEdgeLength to prevent outline collapse.
Raise minRegionArea to remove hole-bearing micro-regions.
Switch partitioning strategy if outlines persistently degrade.

When it happens

Trigger: High maxSimplificationError collapsing a region's outline while its holes survive; maxEdgeLength too large merging outline edges into degenerate paths; very small/thin regions.

Common situations: Tuning maxSimplificationError up for fewer vertices until outlines self-intersect; aggressive contour settings on intricate geometry.

Related errors

AI-assisted analysis of egametang/ET@5cab01f7a8 (2026-08-13). Data as JSON: /api/errors/537d6d3220e4b146. Report an issue: GitHub.