dotnet/wpf · error · ArgumentException

SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo…

Error message

SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, GlyphCount)

What it means

When no clusterMap is provided, GlyphRun.Initialize requires an exact 1:1 correspondence: GlyphCount must equal characters.Count. The message states the collection must have exactly GlyphCount elements, thrown as ArgumentException on the clusterMap parameter.

Solutions

  1. Provide a proper clusterMap instead of relying on the 1:1 assumption
  2. Shape the text so glyph count matches character count for simple scripts
  3. Filter/expand characters so counts align before constructing the run

Example fix

// before: glyphs.Count==1 for 'é' composed as 2 chars, no clusterMap
// after
new GlyphRun(tf, 0, false, 12, glyphs, chars, new int[]{0,0}, null, null, null, false); // clusterMap given
Defensive patterns

Strategy: validation

Validate before calling

if ((clusterMap == null || clusterMap.Length == 0) && glyphIndices.Count != characters.Count)
    throw new InvalidOperationException("1:1 runs require equal counts; otherwise pass a clusterMap");

Type guard

static bool NeedsClusterMap(char[] chars, ushort[] glyphs) => chars.Length != glyphs.Length;

Try / catch

try { var run = new GlyphRun(...); }
catch (ArgumentException ex) when (ex.ParamName == "clusterMap") { /* build clusterMap */ }

Prevention

When it happens

Trigger: Calling the GlyphRun constructor, TryCreate, or EndInit with clusterMap null/empty and glyphIndices.Count != characters.Count — common with ligatures, surrogate pairs, or combining sequences.

Common situations: Mapping Unicode text directly to glyphs without shaping; text containing emoji or CJK surrogate pairs where character count exceeds glyph count assumptions.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/8341b81a5197d973. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/GlyphRun.cs:404

                                        if (clusterMap[i] >= GlyphCount)
                                            throw new ArgumentException(SR.ClusterMapEntryShouldPointWithinGlyphIndices, nameof(clusterMap));
                                    }
                                }
                            }
                            else
                            {
                                throw new ArgumentException(SR.ClusterMapFirstEntryMustBeZero, nameof(clusterMap));
                            }
                        }
                        else
                        {
                            throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, characters.Count), nameof(clusterMap));
                        }
                    }
                    else
                    {
                        if (GlyphCount != characters.Count)
                            throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, GlyphCount), nameof(clusterMap));
                    }
                }

                if (caretStops != null && caretStops.Count != 0)
                {
                    if (caretStops.Count != CodepointCount + 1)
                        throw new ArgumentException(SR.Format(SR.CollectionNumberOfElementsShouldBeEqualTo, CodepointCount + 1), nameof(caretStops));
                }

                if (isSideways && (bidiLevel & 1) != 0)
                    throw new ArgumentException(SR.SidewaysRTLTextIsNotSupported);

                // NOTE:  In previous versions this function would estimate the size
                // of this glyph run's bitmaps and compare it against the theoretical
                // maximum size allowed before rendering falls back to using geometry.
                // This was done in order to produce a managed exception where we might
                // hit overflow or memory allocation issues in native code.
                // We no longer own the code the produces these bitmaps so we can't reliably

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