MathLib: added bound box transform function

2 files changed, 68 insertions, 0 deletions

diff --git a/Common/interface/AdvancedMath.hpp b/Common/interface/AdvancedMath.hpp
index 21a633cc..b48da1bc 100644
--- a/Common/interface/AdvancedMath.hpp
+++ b/Common/interface/AdvancedMath.hpp
@@ -175,6 +175,38 @@ struct BoundBox
 {
     float3 Min;
     float3 Max;
+
+    // Computes new bounding box by applying transform matrix m to the box
+    BoundBox Transform(const float4x4& m) const
+    {
+        BoundBox NewBB;
+        NewBB.Min = float3::MakeVector(m[3]);
+        NewBB.Max = NewBB.Min;
+        float3 v0, v1;
+
+        float3 right = float3::MakeVector(m[0]);
+
+        v0 = right * Min.x;
+        v1 = right * Max.x;
+        NewBB.Min += std::min(v0, v1);
+        NewBB.Max += std::max(v0, v1);
+
+        float3 up = float3::MakeVector(m[1]);
+
+        v0 = up * Min.y;
+        v1 = up * Max.y;
+        NewBB.Min += std::min(v0, v1);
+        NewBB.Max += std::max(v0, v1);
+
+        float3 back = float3::MakeVector(m[2]);
+
+        v0 = back * Min.z;
+        v1 = back * Max.z;
+        NewBB.Min += std::min(v0, v1);
+        NewBB.Max += std::max(v0, v1);
+
+        return NewBB;
+    }
 };
 
 enum class BoxVisibility
diff --git a/Tests/DiligentCoreTest/src/Common/MathLibTest.cpp b/Tests/DiligentCoreTest/src/Common/MathLibTest.cpp
index 35456966..dcf1cfbb 100644
--- a/Tests/DiligentCoreTest/src/Common/MathLibTest.cpp
+++ b/Tests/DiligentCoreTest/src/Common/MathLibTest.cpp
@@ -1910,4 +1910,40 @@ TEST(Common_AdvancedMath, RasterizeTriangle)
     }
 }
 
+TEST(Common_AdvancedMath, TransformBoundBox)
+{
+    BoundBox BB;
+    BB.Min = float3{1, 2, 3};
+    BB.Max = float3{2, 4, 6};
+
+    {
+        float3 Offset{2.5f, 3.125f, -7.25f};
+        auto   TransformedBB = BB.Transform(float4x4::Translation(Offset));
+        EXPECT_EQ(TransformedBB.Min, BB.Min + Offset);
+        EXPECT_EQ(TransformedBB.Max, BB.Max + Offset);
+    }
+
+    {
+        float3 Scale{0.5f, 2.125f, 1.25f};
+        auto   TransformedBB = BB.Transform(float4x4::Scale(Scale));
+        EXPECT_EQ(TransformedBB.Min, BB.Min * Scale);
+        EXPECT_EQ(TransformedBB.Max, BB.Max * Scale);
+    }
+
+    {
+        // clang-format off
+        float4x4 Rotation
+        {
+            0,  1,  0,  0,
+            0,  0,  1,  0,
+           -1,  0,  0,  0,
+            0,  0,  0,  1
+        };
+        // clang-format on
+        auto TransformedBB = BB.Transform(Rotation);
+        EXPECT_EQ(TransformedBB.Min, float3(-6, 1, 2));
+        EXPECT_EQ(TransformedBB.Max, float3(-3, 2, 4));
+    }
+}
+
 } // namespace