XMVectorATan2Est function (directxmath.h)

Article
02/22/2024

Estimates the arctangent of Y/X.

Syntax

XMVECTOR XM_CALLCONV XMVectorATan2Est(
  [in] FXMVECTOR Y,
  [in] FXMVECTOR X
) noexcept;

Parameters

[in] Y

First vector.

[in] X

Second vector.

Return value

Returns a vector. Each component is an estimate of the arctangent of the corresponding Y component divided by the corresponding X component. Each component is in the range (-PI/2, PI/2).

XMVectorATan2Est returns the following values for the specified special input values.

Input Value	Return Value
Y == 0 and X < 0	Pi with the same sign as Y
Y == 0 and X > 0	0 with the same sign as Y
Y != 0 and X == 0	Pi / 2 with the same sign as Y
X == -Infinity and Y is finite	Pi with the same sign as Y
X == +Infinity and Y is finite	0 with the same sign as Y
Y == Infinity and X is finite	Pi / 2 with the same sign as Y
Y == Infinity and X == -Infinity	3Pi / 4 with the same sign as Y
Y == Infinity and X == +Infinity	Pi / 4 with the same sign as Y

Remarks

Est functions offer increased performance at the expense of reduced accuracy. Est functions are appropriate for non-critical calculations where accuracy can be sacrificed for speed. The exact amount of lost accuracy and speed increase are platform dependent.

This function uses a 9-degree minimax approximation.

Platform Requirements

Microsoft Visual Studio 2010 or Microsoft Visual Studio 2012 with the Windows SDK for Windows 8. Supported for Win32 desktop apps, Windows Store apps, and Windows Phone 8 apps.

Requirements

Requirement	Value
Target Platform	Windows
Header	directxmath.h (include DirectXMath.h)