stride3d/stride · error · ArgumentException

Could not parse semantic index from the semantic name

Error message

Could not parse semantic index from the semantic name

What it means

VertexElement's string-based constructor parses an optional numeric index out of the semantic name (e.g. "TEXCOORD0"). If the name matches a pattern with a trailing/numeric component that fails uint.TryParse, the library cannot extract the semantic index and throws ArgumentException.

Solutions

Use a valid semantic name with an integer index suffix, e.g. "TEXCOORD0"
Drop the suffix entirely if no index is needed (index defaults to 0)
Use the explicit-index constructor overload with a plain semantic name like "TEXCOORD" and semanticIndex: 1

Example fix

// before
new VertexElement("TEXCOORDu", PixelFormat.R32G32_Float)
// after
new VertexElement("TEXCOORD0", PixelFormat.R32G32_Float)
// or
new VertexElement("TEXCOORD", 0, PixelFormat.R32G32_Float)

Defensive patterns

Strategy: validation

Validate before calling

static readonly Regex ok = new Regex(@"^(?<name>[A-Za-z]+)(?<idx>\d*)$");
bool IsValidSemantic(string s) { var m = ok.Match(s); return m.Success && (m.Groups["idx"].Value == "" || uint.TryParse(m.Groups["idx"].Value, out _)); }

Try / catch

try { var e = new VertexElement(name, format); } catch (ArgumentException) { useExplicitIndexConstructor(); }

Prevention

Only use integer suffixes on semantic names
Prefer the explicit (name, index, format) constructor to avoid string parsing
Uppercase-only semantic names without extra annotations

When it happens

Trigger: Constructing VertexElement with a semantic name containing a non-numeric index part, e.g. "POSITION_" or "TEXCOORDX" or "COLOR#1".

Common situations: Hand-editing shader semantic names; copying semantics from HLSL with suffixed annotations; typos like "NORMAL01a".

Understand the failure class

Background: "invalid id" errors: invalid identifier format — why libraries reject IDs before lookup, and how to fix them — this error's family across 37 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/0e7fe99cee0a8f0f. Report an issue: GitHub.

Appendix: source

Thrown at sources/engine/Stride.Graphics/VertexElement.cs:100

    ///   <paramref name="semanticName"/> is <see langword="null"/> or an empty <see langword="string"/>.
    /// </exception>
    public VertexElement(string semanticName, PixelFormat format)
        : this()
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(semanticName);

        // All semantics will be upper case
        semanticName = semanticName.ToUpperInvariant();

        var match = MatchSemanticIndex.Match(semanticName);
        if (match.Success)
        {
            // Convert to singleton string in order to speed up things
            // TODO: Stale comment? Use string.Intern?
            this.semanticName = match.Groups[1].Value;

            if (!uint.TryParse(match.Groups[2].Value, out var semanticIndex))
                throw new ArgumentException("Could not parse semantic index from the semantic name", nameof(semanticName));

            this.semanticIndex = (int) semanticIndex;
        }
        else this.semanticName = semanticName;

        this.format = format;
        alignedByteOffset = AppendAligned;

        // Precalculate hashcode
        hashCode = ComputeHashCode();
    }

    /// <summary>
    ///   Initializes a new instance of the <see cref="VertexElement" /> structure.
    /// </summary>
    /// <param name="semanticName">
    ///   The semantic name associated with this element, such as <c>"POSITION"</c>, <c>"TEXCOORD"</c>, or <c>"NORMAL"</c>.
    /// </param>

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