From 3fcd45a23625ae8d6dabf27e1fc610c816cded6b Mon Sep 17 00:00:00 2001
From: Bradley Austin Davis <bdavis@saintandreas.org>
Date: Thu, 8 Dec 2016 10:59:14 -0800
Subject: [PATCH] Optimized method for transforming axis aligned bounding boxes

---
 libraries/shared/src/AABox.cpp | 52 +++++++++-------------------------
 1 file changed, 13 insertions(+), 39 deletions(-)

diff --git a/libraries/shared/src/AABox.cpp b/libraries/shared/src/AABox.cpp
index a3afa220c9..82b815b006 100644
--- a/libraries/shared/src/AABox.cpp
+++ b/libraries/shared/src/AABox.cpp
@@ -568,46 +568,20 @@ void AABox::transform(const Transform& transform) {
     translate(transform.getTranslation());
 }
 
+// Logic based on http://clb.demon.fi/MathGeoLib/nightly/docs/AABB.cpp_code.html#471
 void AABox::transform(const glm::mat4& matrix) {
-    auto minimum = _corner;
-    auto maximum = _corner + _scale;
+    auto halfSize = _scale * 0.5f;
+    auto center = _corner + halfSize;
+    halfSize = abs(halfSize);
+    auto newCenter = transformPoint(matrix, center);
 
-    glm::vec3 bottomLeftNear(minimum.x, minimum.y, minimum.z);
-    glm::vec3 bottomRightNear(maximum.x, minimum.y, minimum.z);
-    glm::vec3 bottomLeftFar(minimum.x, minimum.y, maximum.z);
-    glm::vec3 bottomRightFar(maximum.x, minimum.y, maximum.z);
-    glm::vec3 topLeftNear(minimum.x, maximum.y, minimum.z);
-    glm::vec3 topRightNear(maximum.x, maximum.y, minimum.z);
-    glm::vec3 topLeftFar(minimum.x, maximum.y, maximum.z);
-    glm::vec3 topRightFar(maximum.x, maximum.y, maximum.z);
+    auto mm = glm::transpose(glm::mat3(matrix));
+    vec3 newDir = vec3(
+        glm::dot(glm::abs(vec3(mm[0])), halfSize),
+        glm::dot(glm::abs(vec3(mm[1])), halfSize),
+        glm::dot(glm::abs(vec3(mm[2])), halfSize)
+    );
 
-    glm::vec3 bottomLeftNearTransformed = transformPoint(matrix, bottomLeftNear);
-    glm::vec3 bottomRightNearTransformed = transformPoint(matrix, bottomRightNear);
-    glm::vec3 bottomLeftFarTransformed = transformPoint(matrix, bottomLeftFar);
-    glm::vec3 bottomRightFarTransformed = transformPoint(matrix, bottomRightFar);
-    glm::vec3 topLeftNearTransformed = transformPoint(matrix, topLeftNear);
-    glm::vec3 topRightNearTransformed = transformPoint(matrix, topRightNear);
-    glm::vec3 topLeftFarTransformed = transformPoint(matrix, topLeftFar);
-    glm::vec3 topRightFarTransformed = transformPoint(matrix, topRightFar);
-
-    minimum = glm::min(bottomLeftNearTransformed,
-        glm::min(bottomRightNearTransformed,
-        glm::min(bottomLeftFarTransformed,
-        glm::min(bottomRightFarTransformed,
-        glm::min(topLeftNearTransformed,
-        glm::min(topRightNearTransformed,
-        glm::min(topLeftFarTransformed,
-        topRightFarTransformed)))))));
-
-    maximum = glm::max(bottomLeftNearTransformed,
-        glm::max(bottomRightNearTransformed,
-        glm::max(bottomLeftFarTransformed,
-        glm::max(bottomRightFarTransformed,
-        glm::max(topLeftNearTransformed,
-        glm::max(topRightNearTransformed,
-        glm::max(topLeftFarTransformed,
-        topRightFarTransformed)))))));
-
-    _corner = minimum;
-    _scale = maximum - minimum;
+    _corner = newCenter - newDir;
+    _scale = newDir * 2.0f;
 }