qvec: add 3x3 matrix inverse, row major factory method

common/qvec.cc

@@ -137,6 +137,27 @@ qmat4x4f qv::inverse(const qmat4x4f &input)
     return qmat4x4f(qv::inverse(qmat4x4d(input)));
 }
 
+qmat3x3f qv::inverse(const qmat3x3f &m)
+{
+    qmat4x4d temp {};
+    for (int r = 0; r < 3; ++r) {
+        for (int c = 0; c < 3; ++c) {
+            temp.at(r,c) = m.at(r,c);
+        }
+    }
+
+    temp = qv::inverse(temp);
+
+    // return the upper-left 3x3 matrix
+    qmat3x3f result;
+    for (int r = 0; r < 3; ++r) {
+        for (int c = 0; c < 3; ++c) {
+            result.at(r,c) = temp.at(r,c);
+        }
+    }
+    return result;
+}
+
 qmat2x2f qv::inverse(const qmat2x2f &m)
 {
     // http://www.mathwords.com/i/inverse_of_a_matrix.htm

include/common/qvec.hh

@@ -909,6 +909,19 @@ public:
         std::copy(list.begin(), list.end(), m_values.begin());
     }
 
+    // static factory, row-major order
+    static qmat row_major(std::initializer_list<T> list) {
+        assert(list.size() == NRow * NCol);
+
+        qmat result;
+        for (size_t i = 0; i < NRow; i++) { // for each row
+            for (size_t j = 0; j < NCol; j++) { // for each col
+                result.at(i, j) = *(list.begin() + (i*NCol + j));
+            }
+        }
+        return result;
+    }
+
     // Sort support
     [[nodiscard]] constexpr bool operator<(const qmat &other) const { return m_values < other.m_values; }
     [[nodiscard]] constexpr bool operator<=(const qmat &other) const { return m_values <= other.m_values; }
@@ -1043,6 +1056,7 @@ namespace qv
 [[nodiscard]] qmat4x4d inverse(const qmat4x4d &input);
 
 [[nodiscard]] qmat2x2f inverse(const qmat2x2f &input);
+[[nodiscard]] qmat3x3f inverse(const qmat3x3f &input);
 }; // namespace qv
 
 // returns the normalized direction from `start` to `stop` in the `dir` param

tests/test_light.cc

@@ -871,6 +871,32 @@ TEST_CASE("matrix2x2inv")
     REQUIRE(std::isnan(nanMat.at(0, 0)));
 }
 
+TEST_CASE("matrix3x3inv")
+{
+    std::mt19937 engine(0);
+    std::uniform_real_distribution<float> dis(-4096, 4096);
+
+    qmat3x3f randMat;
+    for (int i = 0; i < 3; i++)
+        for (int j = 0; j < 3; j++)
+            randMat.at(i, j) = dis(engine);
+
+    qmat3x3f randInv = qv::inverse(randMat);
+    REQUIRE_FALSE(std::isnan(randInv.at(0, 0)));
+
+    qmat3x3f prod = randMat * randInv;
+    for (int i = 0; i < 3; i++) {
+        for (int j = 0; j < 3; j++) {
+            float exp = (i == j) ? 1.0f : 0.0f;
+            REQUIRE(fabs(exp - prod.at(i, j)) < 0.001);
+        }
+    }
+
+    // check non-invertible gives nan
+    qmat3x3f nanMat = qv::inverse(qmat3x3f(0));
+    REQUIRE(std::isnan(nanMat.at(0, 0)));
+}
+
 TEST_CASE("matrix4x4inv")
 {
     std::mt19937 engine(0);
@@ -897,6 +923,19 @@ TEST_CASE("matrix4x4inv")
     REQUIRE(std::isnan(nanMat.at(0, 0)));
 }
 
+TEST_CASE("qmat_construct_initialize") {
+    const qmat2x2f test{1,2,3,4}; // column major
+
+    CHECK(qvec2f{1,3} == test.row(0));
+    CHECK(qvec2f{2,4} == test.row(1));
+}
+
+TEST_CASE("qmat_construct_row_major") {
+    const qmat2x2f test = qmat2x2f::row_major({1, 2, 3, 4});
+
+    CHECK(qvec2f{1,2} == test.row(0));
+    CHECK(qvec2f{3,4} == test.row(1));
+}
 }
 TEST_SUITE("trace") {