CompositionAnimation fixes

[zxbmmmmmmmmm]

What does the pull request do?

This pull request removes the Scalar variant type from the composition expression system and standardizes all scalar numeric values to use the Double type. It also introduces a centralized ExpressionKeywords class for managing expression keywords, which improves maintainability and consistency across the codebase. The changes simplify arithmetic and comparison operations, update type mappings, and ensure correct handling of tracked objects and references.

Type System Simplification

• Removed the Scalar variant from ExpressionVariant, consolidating all scalar numeric values under the Double type. This change affects implicit conversions, arithmetic, and comparison operations, which now exclusively use Double for scalar math.
• Updated the type mapping in DelegateExpressionFfi to map float to VariantType.Double instead of the removed Scalar type.

Arithmetic and Comparison Operation Updates

• Refactored arithmetic and comparison operators in ExpressionVariant to remove all logic related to the Scalar type and ensure operations involving scalars use Double. This includes addition, subtraction, multiplication, division, modulus, and comparison operators.

• Fixed a bug in vector division where previously right.Scalar was used; now correctly uses right.Double.

Expression Keyword Centralization

• Introduced the ExpressionKeywords class to centralize keyword constants, replacing scattered string literals throughout the expression parsing and evaluation code.

• Updated ExpressionParser and reference collection logic to use the new ExpressionKeywords class for improved maintainability and consistency. [1] [2]

Object Tracking and Parameter Handling

• Updated object tracking logic in AnimationInstanceBase to correctly handle the this.target keyword using the new centralized keyword class, ensuring the correct object is tracked for target expressions.

Type Casting Logic

• Modified type casting logic in DelegateExpressionFfi to remove support for casting between Double and the removed Scalar type, ensuring only valid type casts are allowed.

What is the current behavior?

First, nothing is written to s_dynamicRegistry(CompositionProperty.cs), thus all composition properties seem not correctly registered. Thus, GetPropertyAnimation method(ServerObjectAnimation.cs) always return default, making ExpressionAnimation completely broken.

Second, VariantPropertyTypes (Generator.cs) does not contain Vector type, so it always generate null for GetVariant parameter .

The last and trickiest, constants like '0.5' are parsed as Scalar, and when we do operations with double values(e.g. Vector3D.X), it will return Invalid value as they're different ExpressionVarient types.

These problems made CompositionAnimation (especially ExpressionAnimation) hard to work properly.

What is the updated/expected behavior with this PR?

20260319-1307-42.2557921.mp4

How was the solution implemented (if it's not obvious)?

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Obsoletions / Deprecations

Fixed issues

#16774
#18784

[Copilot]

Pull request overview

This PR addresses broken composition expression animations by simplifying the expression numeric type system (removing the Scalar variant and standardizing on Double), fixing property lookup for server objects during animation evaluation, and centralizing expression keyword strings to reduce duplication and inconsistencies.

Changes:

• Removed VariantType.Scalar usage paths and updated tests/operators/FFI mappings to use VariantType.Double for scalar math.
• Reworked server-side composition property lookup to rely on ServerObject.GetCompositionProperty(...) instead of a global registry/dictionary path.
• Introduced ExpressionKeywords constants and updated parsing/reference tracking, including special handling for this.target.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/Avalonia.Base.UnitTests/Composition/CompositionAnimationTests.cs	Updates assertions to validate scalar results via .Double instead of .Scalar.
tests/Avalonia.Base.UnitTests/Composition/CompositionAnimationParserTests.cs	Removes Scalar-type branching and expects expression results as Double.
src/tools/DevGenerators/CompositionGenerator/Generator.cs	Expands variant-capable property types to include double and Vector.
src/Avalonia.Base/Rendering/Composition/Server/ServerObjectAnimations.cs	Switches animation property lookup to GetCompositionProperty on the owner.
src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs	Uses GetCompositionProperty for expression property access when not animated.
src/Avalonia.Base/Rendering/Composition/Server/CompositionProperty.cs	Removes the dynamic registry implementation and leaves a simplified registration path.
src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionVariant.cs	Removes Scalar representation and refactors operators/casting accordingly.
src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionParser.cs	Uses centralized ExpressionKeywords for keyword parsing.
src/Avalonia.Base/Rendering/Composition/Expressions/Expression.cs	Adds ExpressionKeywords and updates reference collection for this.target.
src/Avalonia.Base/Rendering/Composition/Expressions/DelegateExpressionFfi.cs	Maps float to VariantType.Double and removes Scalar-related casts.
src/Avalonia.Base/Rendering/Composition/Animations/AnimationInstanceBase.cs	Tracks this.target references by mapping them to the animation’s TargetObject.

Comments suppressed due to low confidence (2)

src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionVariant.cs:441

• Now that scalar literals are VariantType.Double, operator * no longer handles scalar scaling for most vector/matrix/quaternion types. For example, Vector2 * Double / Vector3 * Double / Vector4 * Double will currently return default (invalid) because only Vector * Double is implemented. Please add the missing * Double branches (casting to float where required) for the types that previously supported * Scalar.

            if (left.Type == VariantType.Vector2 && right.Type == VariantType.Vector2)
                return left.Vector2 * right.Vector2;

            if (left.Type == VariantType.Vector && right.Type == VariantType.Vector)
                return Vector.Multiply(left.Vector, right.Vector);
            
            if (left.Type == VariantType.Vector && right.Type == VariantType.Double)
                return left.Vector * right.Double;

src/Avalonia.Base/Rendering/Composition/Expressions/DelegateExpressionFfi.cs:118

• Mapping float to VariantType.Double makes float and double FFI overloads indistinguishable at runtime. The registry will then pick the first matching record based on insertion order, and can also force double values to be cast down to float inside delegates. This is observable with existing built-ins like Vector2(float,float) and Vector2(double,double) / Vector3(float,float,float) and Vector3(double,double,double) which will now share the same signature. Consider normalizing built-in scalar signatures to double (or rejecting duplicate registrations) to avoid order-dependent behavior and precision loss.

        static readonly Dictionary<Type, VariantType> TypeMap = new Dictionary<Type, VariantType>
        {
            [typeof(bool)] = VariantType.Boolean,
            [typeof(float)] = VariantType.Double,
            [typeof(double)] = VariantType.Double,
            [typeof(Vector2)] = VariantType.Vector2,
            [typeof(Vector)] = VariantType.Vector,
            [typeof(Vector3)] = VariantType.Vector3,
            [typeof(Vector3D)] = VariantType.Vector3D,

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Pull request overview

This PR fixes broken Composition/Expression animations by simplifying the expression numeric type system (removing the Scalar variant and standardizing on Double), centralizing expression keyword strings, and adjusting composition property lookup/tracking so expression dependencies and property resolution work correctly.

Changes:

• Remove VariantType.Scalar and migrate scalar parsing/math/casting to VariantType.Double.
• Centralize expression keyword literals via ExpressionKeywords and update parsing/reference collection/tracking (including this.Target).
• Switch composition property lookup to ServerObject.GetCompositionProperty, update generator type support (double, Vector), and add/adjust unit tests.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/Avalonia.Base.UnitTests/Composition/CompositionAnimationTests.cs	Updates scalar assertions to Double and adds new coverage for property lookup + expression tracking.
tests/Avalonia.Base.UnitTests/Composition/CompositionAnimationParserTests.cs	Updates parser test to expect only Double results for scalars.
src/tools/DevGenerators/CompositionGenerator/Generator.cs	Extends variant get-property generation to include double and Vector.
src/Avalonia.Base/Rendering/Composition/Server/ServerObjectAnimations.cs	Uses GetCompositionProperty for animation property resolution; improves subscription invalidation behavior.
src/Avalonia.Base/Rendering/Composition/Server/ServerObject.cs	Routes expression property access through GetCompositionProperty.
src/Avalonia.Base/Rendering/Composition/Server/CompositionProperty.cs	Removes the old global per-type registry mechanics, keeping property creation only.
src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionVariant.cs	Removes Scalar, updates arithmetic/comparison/casting, and standardizes scalar behavior on Double.
src/Avalonia.Base/Rendering/Composition/Expressions/ExpressionParser.cs	Replaces keyword literals with ExpressionKeywords.
src/Avalonia.Base/Rendering/Composition/Expressions/Expression.cs	Introduces ExpressionKeywords and updates reference collection for this.Target.
src/Avalonia.Base/Rendering/Composition/Expressions/DelegateExpressionFfi.cs	Updates type mapping (float → Double) and removes Scalar cast logic.
src/Avalonia.Base/Rendering/Composition/Animations/AnimationInstanceBase.cs	Special-cases reference tracking for this.Target so target object dependencies are subscribed correctly.

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