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diff --git a/src/display/nr-3dutils.h b/src/display/nr-3dutils.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef SEEN_NR_3DUTILS_H
+#define SEEN_NR_3DUTILS_H
+
+/*
+ * 3D utils. Definition of gdouble vectors of dimension 3 and of some basic
+ * functions.
+ *   This looks redundant, why not just use Geom::Point for this?
+ *
+ * Authors:
+ *   Jean-Rene Reinhard <jr@komite.net>
+ *
+ * Copyright (C) 2007 authors
+ *
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#include <2geom/forward.h>
+
+namespace NR {
+
+#define X_3D 0
+#define Y_3D 1
+#define Z_3D 2
+
+/**
+ * a type of 3 gdouble components vectors
+ */
+struct Fvector {
+    Fvector() {
+        v[0] = v[1] = v[2] = 0.0;
+    }
+    Fvector(double x, double y, double z) {
+        v[0] = x;
+        v[1] = y;
+        v[2] = z;
+    }
+    double v[3];
+    double &operator[](unsigned i) { return v[i]; }
+    double operator[](unsigned i) const { return v[i]; }
+};
+
+/**
+ * The eye vector
+ */
+const static Fvector EYE_VECTOR(0, 0, 1);
+
+/**
+ * returns the euclidean norm of the vector v
+ *
+ * \param v a reference to a vector with double components
+ * \return the euclidean norm of v
+ */
+double norm(const Fvector &v);
+
+/**
+ * Normalizes a vector
+ *
+ * \param v a reference to a vector to normalize
+ */
+void normalize_vector(Fvector &v);
+
+/**
+ * Computes the scalar product between two Fvectors
+ *
+ * \param a a Fvector reference
+ * \param b a Fvector reference
+ * \return the scalar product of a and b
+ */
+double scalar_product(const Fvector &a, const Fvector &b);
+
+/**
+ * Computes the normalized sum of two Fvectors
+ *
+ * \param r a Fvector reference where we store the result
+ * \param a a Fvector reference
+ * \param b a Fvector reference
+ */
+void normalized_sum(Fvector &r, const Fvector &a, const Fvector &b);
+
+/**
+ * Applies the transformation matrix to (x, y, z). This function assumes that
+ * trans[0] = trans[3]. x and y are transformed according to trans, z is
+ * multiplied by trans[0].
+ *
+ * \param x a reference to a x coordinate
+ * \param y a reference to a y coordinate
+ * \param z a reference to a z coordinate
+ * \param z a reference to a transformation matrix
+ */
+void convert_coord(double &x, double &y, double &z, Geom::Affine const &trans);
+
+} /* namespace NR */
+
+#endif /* __NR_3DUTILS_H__ */
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :