1
2/*
3 * Copyright 2011 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8#include "SkMatrix.h"
9
10// FIXME: needs to be in a header
11bool SkSetPoly3To3(SkMatrix* matrix, const SkPoint src[3], const SkPoint dst[3]);
12
13static void computeOuterProduct(SkScalar op[4],
14                                const SkPoint pts0[3], const SkPoint& ave0,
15                                const SkPoint pts1[3], const SkPoint& ave1) {
16    sk_bzero(op, 4 * sizeof(op[0]));
17    for (int i = 0; i < 3; i++) {
18        SkScalar x0 = pts0[i].fX - ave0.fX;
19        SkScalar y0 = pts0[i].fY - ave0.fY;
20        SkScalar x1 = pts1[i].fX - ave1.fX;
21        SkScalar y1 = pts1[i].fY - ave1.fY;
22        op[0] += SkScalarMul(x0, x1);
23        op[1] += SkScalarMul(x0, y1);
24        op[2] += SkScalarMul(y0, x1);
25        op[3] += SkScalarMul(y0, y1);
26    }
27}
28
29static SkScalar dot(SkScalar ax, SkScalar ay, SkScalar bx, SkScalar by) {
30    return SkScalarMul(ax, bx) + SkScalarMul(ay, by);
31}
32
33bool SkSetPoly3To3(SkMatrix* matrix, const SkPoint src[3], const SkPoint dst[3]) {
34    const SkPoint& srcAve = src[0];
35    const SkPoint& dstAve = dst[0];
36
37    SkScalar srcOP[4], dstOP[4];
38
39    computeOuterProduct(srcOP, src, srcAve, src, srcAve);
40    computeOuterProduct(dstOP, src, srcAve, dst, dstAve);
41
42    SkScalar det = SkScalarMul(srcOP[0], srcOP[3]) - SkScalarMul(srcOP[1], srcOP[2]);
43
44    // need SkScalarNearlyZeroSquared for this (to match Chrome's fix)
45    if (SkScalarNearlyZero(det)) {
46        return false;
47    }
48
49    SkScalar invDet = SkScalarInvert(det);
50
51    // now compute invDet * [srcOP]T * [dstOP]
52
53    // scale and transpose
54    const SkScalar srcOP0 = SkScalarMul( srcOP[3], invDet);
55    const SkScalar srcOP1 = SkScalarMul(-srcOP[1], invDet);
56    const SkScalar srcOP2 = SkScalarMul(-srcOP[2], invDet);
57    const SkScalar srcOP3 = SkScalarMul( srcOP[0], invDet);
58
59    matrix->reset();
60    matrix->setScaleX(dot(srcOP0, srcOP1, dstOP[0], dstOP[2]));
61    matrix->setSkewX( dot(srcOP2, srcOP3, dstOP[0], dstOP[2]));
62    matrix->setSkewY (dot(srcOP0, srcOP1, dstOP[1], dstOP[3]));
63    matrix->setScaleY(dot(srcOP2, srcOP3, dstOP[1], dstOP[3]));
64    matrix->setTranslateX(dstAve.fX - dot(srcAve.fX, srcAve.fY,
65                                    matrix->getScaleX(), matrix->getSkewX()));
66    matrix->setTranslateY(dstAve.fY - dot(srcAve.fX, srcAve.fY,
67                                    matrix->getSkewY(), matrix->getScaleY()));
68    return true;
69}
70