What causes "Assign back to matrix swizzle is not implemented yet" in stride3d/stride?

Rewrite the shader to assign matrix rows/elements individually instead of via swizzle

stride3d/stride · error · NotImplementedException

Assign back to matrix swizzle is not implemented yet

Error message

Assign back to matrix swizzle is not implemented yet

What it means

During SPIR-V codegen of an assignment, the compiler pattern-matches the assignment target. When the target is a matrix swizzle (e.g. m._m00_m11 = v) it has no implementation, so it throws NotImplementedException — matrix swizzle write-back is simply not yet supported by this SDSL compiler stage.

Solutions

Rewrite the shader to assign matrix rows/elements individually instead of via swizzle
Use a temporary: compute the swizzled result into locals, then assign each element
Express the operation with matrix constructors or index assignment
Implement the missing codegen case in Expression.cs if you control the compiler

Example fix

// before
m._m00_m11 = vec2(a, b);
// after
m[0][0] = a;
m[1][1] = b;

Defensive patterns

Strategy: fallback

Validate before calling

static bool AssignableViaSwizzle(object target) => target is VectorType or ScalarType or PointerType;

Type guard

bool IsMatrixSwizzleTarget(Identifier id, MatrixType t) => id.IsMatrixSwizzle(t, out _);

Try / catch

try { EmitAssignment(target, value); } catch (NotImplementedException e) when (e.Message.Contains("matrix swizzle")) { EmitElementWiseAssignment(target, value); }

Prevention

Avoid assigning through matrix swizzles in SDSL shaders
Assign matrix elements individually or via row/column constructors
Track Stride releases for matrix-swizzle write-back support

When it happens

Trigger: Assigning to a matrix swizzle lvalue (pattern: target is MatrixType or pointer-to-matrix with an identifier that IsMatrixSwizzle) inside an SDSL shader being translated to SPIR-V.

Common situations: Writing GLSL-style code like mat._11_22 = ... ported from other shading languages; auto-translated shaders that assume swizzle assignment works for matrices.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/53d7ee158502dc88. Report an issue: GitHub.

Appendix: source

Thrown at sources/shaders/Stride.Shaders.Parsers/Parsing/SDSL/AST/Expression.cs:792

                        var bufferValue = builder.Convert(context, rvalue, resultType);
                        builder.Insert(new OpImageWrite(buffer.Id, location.Id, bufferValue.Id, null, []));
                        // We stop there
                        return;
                    }
                // ImageWrite
                case (PointerType { BaseType: TextureType textureType }, IndexerExpression indexer):
                    {
                        var resultType = textureType.ReturnType;
                        var image = builder.AsValue(context, lvalueBase);

                        var imageCoordValue = ConvertTexCoord(context, builder, textureType, indexer.Index.CompileAsValue(table, compiler), ScalarType.Int);
                        var texelValue = builder.Convert(context, rvalue, resultType);
                        builder.Insert(new OpImageWrite(image.Id, imageCoordValue.Id, texelValue.Id, null, []));
                        // We stop there
                        return;
                    }
                case (PointerType { BaseType: MatrixType } or MatrixType, Identifier { Name: var swizzle } id) when id.IsMatrixSwizzle((MatrixType)currentValueType.GetValueType(), out var swizzles):
                    throw new NotImplementedException("Assign back to matrix swizzle is not implemented yet");
                case (PointerType { BaseType: VectorType or ScalarType } or VectorType or ScalarType, Identifier { Name: var swizzle } id) when id.IsVectorSwizzle():
                    // Swizzle: we transform the value to assign accordingly

                    // We load the original value (if pointer)
                    var lvalueType = currentValueType;
                    if (lvalueType is PointerType p)
                    {
                        lvalueBase = new(builder.InsertData(new OpLoad(context.GetOrRegister(p.BaseType), context.Bound++, lvalueBase.Id, null, [])));
                        lvalueType = p.BaseType;
                    }

                    // Shuffle with new data
                    switch (lvalueType)
                    {
                        case VectorType v:
                            var shuffleIndices = shuffleBuffer[..v.Size];
                            // Default: lvalue
                            for (int j = 0; j < v.Size; ++j)

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