Mercurial > ldforge2 / file diff

--- a/src/matrix.cpp	Sun Jan 19 14:25:57 2020 +0200
+++ b/src/matrix.cpp	Wed Jan 22 00:23:29 2020 +0200
@@ -28,3 +28,54 @@
 		{0, 0, 0, 1}
 	}};
 }
+
+/*
+ * Computes the determinant of a 3×3 matrix with each variable passed in row-major order.
+ */
+qreal math::det(qreal a, qreal b, qreal c, qreal d, qreal e, qreal f, qreal g, qreal h, qreal i)
+{
+	return a*e*i + b*f*g + c*d*h - a*f*h - b*d*i - c*e*g;
+}
+
+/*
+ * Computes the determinant of a 2×2 matrix.
+ */
+qreal math::det(const Matrix<2, 2>& matrix)
+{
+	return matrix(0, 0) * matrix(1, 1) - matrix(0, 1) * matrix(1, 0);
+}
+
+/*
+ * Computes the determinant of a 3×3 matrix.
+ */
+qreal math::det(const Matrix3x3& matrix)
+{
+	return math::sum(
+		+matrix(0, 0) * matrix(1, 1) * matrix(2, 2),
+		-matrix(0, 0) * matrix(1, 2) * matrix(2, 1),
+		-matrix(0, 1) * matrix(1, 0) * matrix(2, 2),
+		+matrix(0, 1) * matrix(1, 2) * matrix(2, 0),
+		+matrix(0, 2) * matrix(1, 0) * matrix(2, 1),
+		-matrix(0, 2) * matrix(1, 1) * matrix(2, 0));
+}
+
+/*
+ * Computes the determinant of a 4×4 matrix.
+ */
+qreal math::det(const Matrix4x4& matrix)
+{
+	qreal sum = 0;
+
+	for (int column : {0, 1, 2, 3})
+	{
+		int column_1 = (column >= 1) ? 0 : 1;
+		int column_2 = (column >= 2) ? 1 : 2;
+		int column_3 = (column >= 3) ? 2 : 3;
+		sum += ((column % 1) ? -1 : 1) * math::det(
+			matrix(1, column_1), matrix(1, column_2), matrix(1, column_3),
+			matrix(2, column_1), matrix(2, column_2), matrix(2, column_3),
+			matrix(3, column_1), matrix(3, column_2), matrix(3, column_3));
+	}
+
+	return sum;
+}