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1 /*
2  * Copyright 2014 Google Inc.
3  *
4  * Use of this source code is governed by a BSD-style license that can be
5  * found in the LICENSE file.
6  */
7 
8 #ifndef SkMatrix22_DEFINED
9 #define SkMatrix22_DEFINED
10 
11 #include "SkPoint.h"
12 
13 class SkMatrix;
14 
15 /** Find the Givens matrix G, which is the rotational matrix
16  *  that rotates the vector h to the positive hoizontal axis.
17  *  G * h = [hypot(h), 0]
18  *
19  *  This is equivalent to
20  *
21  *  SkScalar r = h.length();
22  *  SkScalar r_inv = r ? SkScalarInvert(r) : 0;
23  *  h.scale(r_inv);
24  *  G->setSinCos(-h.fY, h.fX);
25  *
26  *  but has better numerical stability by using (partial) hypot,
27  *  and saves a multiply by not computing r.
28  */
29 void SkComputeGivensRotation(const SkVector& h, SkMatrix* G);
30 
31 #endif
32