From 43ade068c9ab55936ccecd877ec83d8580823f72 Mon Sep 17 00:00:00 2001
From: Stephen Seo <seo.disparate@gmail.com>
Date: Thu, 2 May 2024 13:13:43 +0900
Subject: [PATCH] Fix internal getting-normals function

Translation could have caused errors getting the three normals for the
sides of a box. The internal normals-fetching function was therefore
made more robust.
---
 src/sc_sacd.cpp | 86 ++++++++++++++++++++++++++++++++++++++-----------
 src/test.cpp    | 23 +++++++++++++
 2 files changed, 91 insertions(+), 18 deletions(-)

diff --git a/src/sc_sacd.cpp b/src/sc_sacd.cpp
index 52d7066..337b466 100644
--- a/src/sc_sacd.cpp
+++ b/src/sc_sacd.cpp
@@ -63,34 +63,84 @@ SC_SACD_Vec3 operator*(const SC_SACD_Mat4 &mat, const SC_SACD_Vec3 &vec) {
 std::vector<SC_SACD_Vec3> SC_SACD_Get_Box_Normals(
     const SC_SACD_Generic_Box *box) {
   std::vector<SC_SACD_Vec3> normals;
+  SC_SACD_Vec3 a, b, c;
 
-  normals.emplace_back(SC_SACD_Vec3{1.0F, 0.0F, 0.0F});
-  normals.back() = box->transform * normals.back();
+  // Facing positive x-axis.
+  a.x = 0.0F;
+  a.y = 0.0F;
+  a.z = 0.0F;
 
-  normals.emplace_back(SC_SACD_Vec3{0.0F, 1.0F, 0.0F});
-  normals.back() = box->transform * normals.back();
+  b.x = 0.0F;
+  b.y = 1.0F;
+  b.z = 0.0F;
 
-  normals.emplace_back(SC_SACD_Vec3{0.0F, 0.0F, 1.0F});
-  normals.back() = box->transform * normals.back();
+  c.x = 0.0F;
+  c.y = 0.0F;
+  c.z = 1.0F;
+
+  a = box->transform * a;
+  b = box->transform * b;
+  c = box->transform * c;
+
+  b = b - a;
+  c = c - a;
+
+  normals.push_back(SC_SACD_Cross_Product(b, c));
+
+  // Facing positive y-axis.
+  a.x = 0.0F;
+  a.y = 0.0F;
+  a.z = 0.0F;
+
+  b.x = 1.0F;
+  b.y = 0.0F;
+  b.z = 0.0F;
+
+  c.x = 0.0F;
+  c.y = 0.0F;
+  c.z = -1.0F;
+
+  a = box->transform * a;
+  b = box->transform * b;
+  c = box->transform * c;
+
+  b = b - a;
+  c = c - a;
+
+  normals.push_back(SC_SACD_Cross_Product(b, c));
+
+  // Facing positive z-axis.
+  a.x = 0.0F;
+  a.y = 0.0F;
+  a.z = 0.0F;
+
+  b.x = 0.0F;
+  b.y = 1.0F;
+  b.z = 0.0F;
+
+  c.x = -1.0F;
+  c.y = 0.0F;
+  c.z = 0.0F;
+
+  a = box->transform * a;
+  b = box->transform * b;
+  c = box->transform * c;
+
+  b = b - a;
+  c = c - a;
+
+  normals.push_back(SC_SACD_Cross_Product(b, c));
 
   return normals;
 }
 
 std::vector<SC_SACD_Vec3> SC_SACD_Get_Box_Normals_Normalized(
     const SC_SACD_Generic_Box *box) {
-  std::vector<SC_SACD_Vec3> normals;
+  std::vector<SC_SACD_Vec3> normals = SC_SACD_Get_Box_Normals(box);
 
-  normals.emplace_back(SC_SACD_Vec3{1.0F, 0.0F, 0.0F});
-  normals.back() = box->transform * normals.back();
-  normals.back() = normals.back() / SC_SACD_Vec3_Length(normals.back());
-
-  normals.emplace_back(SC_SACD_Vec3{0.0F, 1.0F, 0.0F});
-  normals.back() = box->transform * normals.back();
-  normals.back() = normals.back() / SC_SACD_Vec3_Length(normals.back());
-
-  normals.emplace_back(SC_SACD_Vec3{0.0F, 0.0F, 1.0F});
-  normals.back() = box->transform * normals.back();
-  normals.back() = normals.back() / SC_SACD_Vec3_Length(normals.back());
+  for (auto &normal : normals) {
+    normal = normal / std::sqrt(SC_SACD_Dot_Product(normal, normal));
+  }
 
   return normals;
 }
diff --git a/src/test.cpp b/src/test.cpp
index bebaccc..77acd62 100644
--- a/src/test.cpp
+++ b/src/test.cpp
@@ -568,6 +568,29 @@ int main() {
       CHECK_FLOAT(result.y, std::sqrt(2.0F));
     }
   }
+
+  // Box collision with transform that has translation.
+  {
+    SC_SACD_Generic_Box a = SC_SACD_Generic_Box_Default();
+    SC_SACD_Generic_Box b = SC_SACD_Generic_Box_Default();
+
+    a.width = 1.1F;
+    a.height = 1.1F;
+    b.width = 1.1F;
+    b.height = 1.1F;
+    a.transform = SC_SACD_Translate_Mat4(-1.0F, 0.0F, 0.0F);
+    b.transform = SC_SACD_Translate_Mat4(0.0F, -1.0F, 0.0F);
+
+    CHECK_TRUE(SC_SACD_Generic_Box_Collision(&a, &b));
+
+    a.width = 0.9F;
+    a.height = 0.9F;
+    b.width = 0.9F;
+    b.height = 0.9F;
+
+    CHECK_FALSE(SC_SACD_Generic_Box_Collision(&a, &b));
+  }
+
   std::cout << "Checks checked: " << checks_checked << '\n'
             << "Checks passed:  " << checks_passed << '\n';