Decompiler

The decompiler walks an existing UMaterial or UMaterialFunction node graph and writes an equivalent DreamShaderLang source file. It is how you move a material that already exists into the language without rebuilding it by hand.

Invoking it

Both editor routes require exactly one selected asset, write the file, and then open it in your preferred editor — see Editor Tools. The headless route is on Commandlet.

A progress dialog appears after a 0.25 s delay, titled Decompiling Material '{Asset}'... or Decompiling Material Function '{Asset}'..., with one frame per visited node. It is suppressed in commandlet runs.

Where the file goes

<SourceDirectory> is the Source Directory project setting, DShader by default. Layers and layer blends get their own directories, and the class test is ordered blend-first, so a layer blend never lands in Layers.

Inside the category directory the asset's package path becomes the relative file path, one directory per package segment:

/Game/Materials/Metal/M_Steel
  →  <Project>/DShader/Decompiled/Materials/Game/Materials/Metal/M_Steel.dsm

Passing -Out= to the commandlet overrides the whole computation and writes exactly where told (after path normalization). The editor routes never take an override.

The name inside the file

The Name= written inside the file is not the file path. It is Decompiled/<Category>/<package segments>, with \ / . : replaced by _ in each segment:

/Game/Materials/Metal/M_Steel
  →  Shader(Name="Decompiled/Materials/Game/Materials/Metal/M_Steel")

File layout

// Decompiled from <full object path>
[// Warning: <text>]…

[<VirtualFunction declaration>]…

{ Shader | ShaderFunction | ShaderLayer | ShaderLayerBlend }(Name="<generated name>")
{
    [Properties = { … }]
    [Inputs     = { … }]   // function kinds only
    [Settings   = { … }]   // Shader only
    [Outputs    = { … }]
    [Graph      = { … }]
    [Layout     = { … }]
}

The Settings block of a decompiled Shader always begins with Domain, ShadingModel and BlendMode, emitted unconditionally. Every other setting is emitted only when it differs from the UMaterial class default; the round-trip set is on Material Settings. When a Base.FrontMaterial binding was decompiled the shading model is forced to Substrate, because a Substrate material's own shading-model enum does not describe its surface.

Outputs declares one variable per connected material property and binds it, in this fixed order:

EmissiveColor, BaseColor, Metallic, Specular, Roughness, Anisotropy, Opacity, OpacityMask,
Normal, Tangent, WorldPositionOffset, SubsurfaceColor, CustomData0, CustomData1,
AmbientOcclusion, Refraction, PixelDepthOffset, MaterialAttributes,
FrontMaterial        (UE 5.4 and newer only)

Unconnected properties are skipped entirely.

What round-trips faithfully

The node walker has a curated case for each class below. Everything else falls through to the generic fallback.

Emitted as DreamShaderLang syntax

Unconnected operand pins fall back to the node's own constant property when it has one — Min, Max, LinearInterpolate, Power and Clamp all read their Const* values — otherwise to a literal 0.0.

Emitted as a property declaration

These become entries in the Properties section and are referenced by name in the Graph. Names are uniquified, and a ParameterName= metadata entry is added whenever the DreamShaderLang identifier had to differ from the asset's parameter name.

A TextureSampleParameter2D with any connected input pin is emitted as a curated UE.Expression instead, carrying its parameter arguments and its sampler arguments together since 1.3.7. Its RGBA output is emitted once into a named temporary; every other pin becomes a swizzle of it.

Emitted as a curated UE.Expression

These keep a hand-written argument list rather than a reflection dump, so only the properties that actually differ from the node default appear.

The UE.Expression fallback

Any class without a case above is exported as a generic UE.Expression call, and the decompiler records a warning for it.

The argument list is built in two passes:

1. Every connected input pin, named after the pin, in pin order.
2. Every reflected literal property whose value differs from the class default since 1.3.7.

A property is exported in pass 2 only when all of these hold:

Names are compared after normalization, so bTwoSided and Two Sided collide.

OutputType is always emitted, resolved from the real output index. When a named output selector (Output= / OutputName=) is present, OutputIndex is suppressed, because the generator rejects a call carrying both. Calls with more than three arguments, or longer than 120 characters, are emitted across multiple lines.

Layout export

Controlled by the Export Decompiled Layout project setting, default on. When on, the file gets a Layout section:

Comment boxes whose text begins with DreamShader: are skipped — those are generated markers, not authored comments.

Independently of the setting, each expression is also assigned to the smallest comment box that encloses it, and those assignments become #Region / #EndRegion directives around the corresponding Graph statements. Turning layout export off removes the Layout block but not the regions. See Layout and #Region.

Diagnostics

Runtime substitutions are written {Placeholder}.

Warnings written into the file

Each is emitted once, as a // Warning: … comment under the // Decompiled from … header line. None of them fails the export.

Export failures

Editor toasts

Logs: Exported Material '{Asset}' to DSM '{File}'. at Display, and Failed to export Material '{Asset}' to DSM: {Error} at Warning.

Known gaps

Verified behaviour of 1.5.0. Every row is something the exported file will not reproduce. Check the ones that apply to your asset before treating the source file as the truth.

Example

Export /Game/Materials/M_Steel headlessly, then inspect the result:

& "$Engine\Binaries\Win64\UnrealEditor-Cmd.exe" "I:\Project\Project.uproject" `
    -run=DreamShader decompile -Asset="/Game/Materials/M_Steel" `
    -unattended -nopause -nosplash -stdout -log

DreamShader decompiled '/Game/Materials/M_Steel.M_Steel' to
'I:/Project/DShader/Decompiled/Materials/Game/Materials/M_Steel.dsm'.

The written file:

// Decompiled from /Game/Materials/M_Steel.M_Steel
Shader(Name="Decompiled/Materials/Game/Materials/M_Steel")
{
    Properties = {
        ScalarParameter Roughness_0 = 0.35 [ParameterName="Roughness"];
        VectorParameter Tint = float4(0.8, 0.8, 0.82, 1.0);
    }
    Settings = {
        Domain = "Surface";
        ShadingModel = "DefaultLit";
        BlendMode = "Opaque";
    }

    Outputs = {
        float3 BaseColor;
        float Metallic;
        float Roughness;

        Base.BaseColor = BaseColor;
        Base.Metallic  = Metallic;
        Base.Roughness = Roughness;
    }

    Graph = {
        BaseColor = Tint.rgb;
        Metallic  = 1.0;
        Roughness = saturate(Roughness_0);
    }

    Layout = {
        Node(Var="Tint", X=-640, Y=-208);
        Node(Var="Roughness_0", X=-640, Y=48);
    }
}

Note ParameterName="Roughness" on the first property. The asset's parameter is called Roughness, but that identifier was already taken in this file, so the declaration was uniquified to Roughness_0 and the real parameter name preserved as metadata — otherwise the regenerated material would expose a parameter under the wrong name. See Metadata and Groups.

Where next