---
name: "rtcIntersect1"
section: "3embree4"
platform: "linux"
package: "embree"
version: "4.4.1-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/rtcIntersect1/3embree4"
---

# rtcIntersect1(3embree4)

### NAME

-

  ```
  rtcIntersect1 - finds the closest hit for a single ray
  ```

### SYNOPSIS

-

  ```
  #include <embree4/rtcore.h>
  void rtcIntersect1(
    RTCScene scene,
    struct RTCRayHit* rayhit
    struct RTCIntersectArguments* args = NULL
  );
  ```

### DESCRIPTION

The `rtcIntersect1` function finds the closest hit of a single ray (`rayhit` argument) with the scene (`scene` argument). The provided ray/hit structure contains the ray to intersect and some hit output fields that are filled when a hit is found. The passed optional arguments struct (`args` argument) can get used for advanced use cases, see section \[rtcInitIntersectArguments\] for more details.

To trace a ray, the user has to initialize the ray origin (`org` ray member), ray direction (`dir` ray member), ray segment (`tnear`, `tfar` ray members), ray mask (`mask` ray member), and set the ray flags to `0` (`flags` ray member). The ray time (`time` ray member) must be initialized to a value in the range $\[0, 1\]. The ray segment has to be in the range \[0, ∞\], thus ranges that start behind the ray origin are not valid, but ranges can reach to infinity. See Section \[RTCRay\] for the ray layout description.

The geometry ID (`geomID` hit member) of the hit data must be initialized to `RTC_INVALID_GEOMETRY_ID` (-1).

When no intersection is found, the ray/hit data is not updated. When an intersection is found, the hit distance is written into the `tfar` member of the ray and all hit data is set, such as unnormalized geometry normal in object space (`Ng` hit member), local hit coordinates (`u`, `v` hit member), instance ID stack (`instID` hit member), geometry ID (`geomID` hit member), and primitive ID (`primID` hit member). See Section \[RTCHit\] for the hit layout description.

If the instance ID stack has a prefix of values not equal to `RTC_INVALID_GEOMETRY_ID`, the instance ID on each level corresponds to the geometry ID of the hit instance of the higher-level scene, the geometry ID corresponds to the hit geometry inside the hit instanced scene, and the primitive ID corresponds to the n-th primitive of that geometry.

If level 0 of the instance ID stack is equal to `RTC_INVALID_GEOMETRY_ID`, the geometry ID corresponds to the hit geometry inside the top-level scene, and the primitive ID corresponds to the n-th primitive of that geometry.

The implementation makes no guarantees that primitives whose hit distance is exactly at (or very close to) `tnear` or `tfar` are hit or missed. If you want to exclude intersections at `tnear` just pass a slightly enlarged `tnear`, and if you want to include intersections at `tfar` pass a slightly enlarged `tfar`.

-

  ```

  ```

The ray/hit structure must be aligned to 16 bytes.

### EXIT STATUS

For performance reasons this function does not do any error checks, thus will not set any error flags on failure.

### SEE ALSO

\[rtcOccluded1\], \[rtcIntersect4/8/16\], \[RTCRayHit\], \[rtcInitIntersectArguments\]