What Is PxLess in NVIDIA PhysX?

PxLess is a templated struct defined within the NVIDIA PhysX SDK, located in the header PxBasicTemplates.h. It provides a simple yet essential function: an inline comparator that evaluates whether one object a is less than another object b, using the operator() syntax in C++

To break it down:

• “PxLess” is not a standalone type, but a generic comparator—patterned like std::less—used throughout the PhysX engine’s internal operations.

• Its signature looks like this:

  template<typename A>
struct PxLess {
inline bool operator()(const A &a, const A &b) const;
};


This enables template-based comparisons, offering flexibility across different data types.

Inner Workings of the PxLess Template

At its core, PxLess implements a simple yet powerful mechanism via its operator():

• Accepts two const references—a and b—of the same template type A.

• Returns a boolean result indicating whether a is less than b.

Under the hood, it relies entirely on the definition of the < operator for the type A. This means it can be used for any data type that supports less-than comparisons, whether built-in primitives (like int or float) or user-defined classes that overload <.

In practice, PxLess acts very much like:

Although PhysX’s internal implementation may vary slightly, the behavior remains consistent with this pattern

Use Cases of PxLess within PhysX

PxLess is employed in several common scenarios in the PhysX SDK to aid internal data structuring and logic:

1. Sorting and Ordered Data Structures

PhysX frequently uses sorted arrays, sets, and other containers that require comparators to maintain order. PxLess provides a lightweight, type-agnostic way to compare elements for sorting algorithms and data structure invariants.

2. Algorithmic Operations

Algorithms such as binary searches, unique filtering, or other comparisons often rely on generic comparator templates—PxLess fits seamlessly into these operations.

3. Template-Based API Consistency

By offering a templated comparator, PhysX maintains consistent behavior across object types without manual duplication, embracing DRY (Don’t Repeat Yourself) principles.

Benefits and Advantages of Using PxLess

Here’s why PxLess matters:

1. Type Agnosticism

As a template, PxLess works with any type A that supports <, offering immense flexibility.

2. Performance

Being inline, PxLess eliminates function-call overhead. The compiler optimizes the comparison at compile time, resulting in zero runtime cost for simple comparisons.

3. Clean Abstraction

Developers can rely on a consistent comparator across the PhysX framework instead of writing multiple variations manually.

4. Maintains Consistency

Using a single struct ensures predictable behavior, especially with user-defined types that only implement <.

Evolution of PxLess Across PhysX SDK Versions

PxLess has remained a stable component in multiple versions of the PhysX SDK. I reviewed documentation from:

• PhysX 5.1.2

• PhysX 5.3.0

• PhysX 5.4.1

Across these versions, PxLess is consistently defined in the include/foundation/PxBasicTemplates.h file with the same templated signature and behavior. This underscores the struct’s stability and backward compatibility—a hallmark of a well-architected library component.

Notably:

• PhysX 5.1.2 (last updated Dec 12, 2022) includes PxLess

• PhysX 5.3.0 documentation (updated Nov 1, 2023) continues to include PxLess

• PhysX 5.4.1 (updated Jul 23, 2024) still defines PxLess identically

This continuity highlights NVIDIA’s commitment to maintaining core utility templates across releases.

Best Practices & Recommendations for Developers

1. Use PxLess for Default Comparisons

When implementing custom containers or algorithms within PhysX, prefer PxLess for comparator functionality—this ensures consistency with the engine’s native behavior.

2. Override Only When Necessary

If comparing complex user-defined types where the default < operator doesn’t capture your intention, override < in your class or write a custom comparator struct—but do so consciously.

3. Keep Inlining in Mind

PxLess is designed as inline, making it ideal for high-performance, repeatedly-invoked operations without overhead. Always review your compiler’s optimization settings to ensure inlining is preserved.

4. Leverage Templates Safely

Avoid using PxLess on types without a defined < operator—this will result in compile-time errors. Confirm your types are comparable.

5. Stay Aware of Future Changes

While PxLess has been stable historically, always reference the latest documentation when updating or migrating your project to ensure API consistency.

Conclusion

PxLess is a small, yet powerful templated comparator inside NVIDIA’s PhysX SDK—a structural mimic of std::less, but tailored for PhysX’s needs. Defined consistently across multiple SDK versions (5.1.2, 5.3.0, and 5.4.1), it provides a lightweight, inline, and generic solution for comparison operations across varied types

By understanding and correctly using PxLess, developers ensure standardized, performant comparisons aligned with PhysX’s core architecture—reinforcing both consistency and efficiency within their physics-driven projects.

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