From 9a2eb878a2acc4b4f9bb304109de7c66db11cfa8 Mon Sep 17 00:00:00 2001
From: Kumikaya <3411015214@qq.com>
Date: Sun, 25 Aug 2024 22:13:23 +0800
Subject: [PATCH] Fix underflow panic in `InitTriInfo` (#14893)

# Objective

- Fix #14874

## Solution

- Change the place where a panic occurs from `t < iNrTrianglesIn - 1` to
`t + 1 < iNrTrianglesIn`.

## Testing

- After the fix, the following code runs successfully without any panic.

```rust
use bevy::prelude::Mesh;
use bevy_render::{
    mesh::{Indices, PrimitiveTopology},
    render_asset::RenderAssetUsages,
};

const POSITIONS: &[[f32; 3]] = &[[0.0, 1.0, 0.0], [0.0, 0.0, 0.0], [0.0, 1.0, 0.0]];

const NORMALS: &[[f32; 3]] = &[[0.0, 0.0, 0.0], [0.0, 0.0, 0.0], [0.0, 0.0, 0.0]];

const INDICES: &[u32] = &[0, 1, 2];

const UVS: &[[f32; 2]] = &[[0.0, 1.0], [0.0, 0.0], [0.0, 1.0]];

fn main() {
    let mut mesh = Mesh::new(
        PrimitiveTopology::TriangleList,
        RenderAssetUsages::default(),
    );

    mesh.insert_attribute(Mesh::ATTRIBUTE_POSITION, POSITIONS.to_vec());
    mesh.insert_attribute(Mesh::ATTRIBUTE_UV_0, UVS.to_vec());
    mesh.insert_attribute(Mesh::ATTRIBUTE_NORMAL, NORMALS.to_vec());
    mesh.insert_indices(Indices::U32(INDICES.to_vec()));
    mesh.generate_tangents().ok();

}

```

## Migration Guide

- No breaking changes introduced.
---
 crates/bevy_mikktspace/src/generated.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/bevy_mikktspace/src/generated.rs b/crates/bevy_mikktspace/src/generated.rs
index 592e1679e5..2589e3930b 100644
--- a/crates/bevy_mikktspace/src/generated.rs
+++ b/crates/bevy_mikktspace/src/generated.rs
@@ -253,6 +253,10 @@ pub unsafe fn genTangSpace<I: Geometry>(geometry: &mut I, fAngularThreshold: f32
         t += 1
     }
     iNrTrianglesIn = iTotTris - iDegenTriangles;
+
+    if iNrTrianglesIn <= 0 {
+        return false;
+    }
     DegenPrologue(
         pTriInfos.as_mut_ptr(),
         piTriListIn.as_mut_ptr(),
@@ -1030,7 +1034,7 @@ unsafe fn InitTriInfo<I: Geometry>(
         }
         f += 1
     }
-    while t < iNrTrianglesIn - 1 {
+    while t + 1 < iNrTrianglesIn {
         let iFO_a: i32 = (*pTriInfos.offset(t as isize)).iOrgFaceNumber;
         let iFO_b: i32 = (*pTriInfos.offset((t + 1) as isize)).iOrgFaceNumber;
         if iFO_a == iFO_b {