# simd_insphere Tests if a single-precision point lies inside, on, or outside a sphere. ``` static float simd_insphere(simd_float3 __x, simd_float3 __a, simd_float3 __b, simd_float3 __c, simd_float3 __d); ``` ## Parameters `__x` The point that the function tests. `__a` The first point that determines the sphere. `__b` The second point that determines the sphere. `__c` The third point that determines the sphere. `__d` The fourth point that determines the sphere. ## Return Value A value that indicates whether the point lies inside, on, or outside the specified sphere. ## Discussion If the points `a`, `b`, `c`, and `d` describe a positively-oriented sphere (that is, the sphere’s normals point away from its center), the function returns: - A positive value if `x` is inside the sphere - Zero if `x` is on the sphere - A negative value if `x` is outside the sphere The function flips sign of the return value if the sphere is negatively-oriented (that is, the sphere’s normals point towards its center). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)