RTCHitN(3)

💖 RTCHitN 💖

okay bestie, so this one is RTCHitN from the Embree Ray Tracing Kernels 4 manual, section 3 (the library functions girlies 🫶). she's a hit packet of runtime size and she is literally the moment. let's get into it ✨

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🌸 NAME 🌸

RTCHitN — hit packet of runtime size 💅

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✨ SYNOPSIS ✨

#include <embree4/rtcore.h>

struct HitN;

float& RTCHitN_Ng_x(RTCHitN* hit, unsigned int N, unsigned int i);
float& RTCHitN_Ng_y(RTCHitN* hit, unsigned int N, unsigned int i);
float& RTCHitN_Ng_z(RTCHitN* hit, unsigned int N, unsigned int i);

float& RTCHitN_u(RTCHitN* hit, unsigned int N, unsigned int i);
float& RTCHitN_v(RTCHitN* hit, unsigned int N, unsigned int i);

unsigned& RTCHitN_primID(RTCHitN* hit, unsigned int N, unsigned int i);
unsigned& RTCHitN_geomID(RTCHitN* hit, unsigned int N, unsigned int i);
unsigned& RTCHitN_instID(RTCHitN* hit, unsigned int N, unsigned int i, unsigned int level);

look at her. she's serving function signatures 🎀 every single one returns a reference, not a copy, so you can write right back into the packet. iykyk.

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🦋 DESCRIPTION 🦋

so here's the tea ☕ sometimes you don't know your hit packet size at compile time. like, at all. the big one: when Embree hands you back a hit packet inside the RTCFilterFuncN callback function — surprise, bestie, runtime vibes only 🙈

that's exactly when Embree pulls out the RTCHitN type for hit packets. that's her whole job. main character energy.

⚠️ okay important: these hit packets can only have sizes of 1, 4, 8, or 16. no other packet size will be used. periodt. don't come at her with a 3, she will not answer the phone 💀

now, you've got two whole routes and both are valid, pick your fighter:

1. implement different special code paths for each of those possible packet sizes, and cast the hit to the appropriate hit packet type 👑
2. implement one general code path that uses the RTCHitN_XXX helper functions to access hit packet components 🌈

and those helper functions? they're so simple it's giving wholesome. each one takes:

• a pointer to the hit packet — that's the hit argument 🎀
• the packet size — that's the N argument 🌸

and it returns a reference to a component (like, say, the x component of Ng ✨) of the i-th hit of the packet — that's the i argument 💖

so: hit, N, i. pointer, size, index. that's the whole recipe. slay.

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💀 EXIT STATUS 💀

nothing here bestie 😭 this section is literally empty in the original. she said "no exit status, we return references, we don't do exits." iconic behaviour honestly 💅

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🎀 SEE ALSO 🎀

• [RTCRayN]

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and that's the page, fr fr 🦋 this was section 3 of the Embree Ray Tracing Kernels 4 manual — RTCHitN(3) — so go forth, check your N, and only ever pass 1, 4, 8, or 16 💖✨🎀 no cap.