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/*
* Copyright 2011 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkMatrix.h"
#include "SkMalloc.h"
// FIXME: needs to be in a header
bool SkSetPoly3To3(SkMatrix* matrix, const SkPoint src[3], const SkPoint dst[3]);
static void computeOuterProduct(SkScalar op[4],
const SkPoint pts0[3], const SkPoint& ave0,
const SkPoint pts1[3], const SkPoint& ave1) {
sk_bzero(op, 4 * sizeof(op[0]));
for (int i = 0; i < 3; i++) {
SkScalar x0 = pts0[i].fX - ave0.fX;
SkScalar y0 = pts0[i].fY - ave0.fY;
SkScalar x1 = pts1[i].fX - ave1.fX;
SkScalar y1 = pts1[i].fY - ave1.fY;
op[0] += x0 * x1;
op[1] += x0 * y1;
op[2] += y0 * x1;
op[3] += y0 * y1;
}
}
static SkScalar dot(SkScalar ax, SkScalar ay, SkScalar bx, SkScalar by) {
return ax * bx + ay * by;
}
bool SkSetPoly3To3(SkMatrix* matrix, const SkPoint src[3], const SkPoint dst[3]) {
const SkPoint& srcAve = src[0];
const SkPoint& dstAve = dst[0];
SkScalar srcOP[4], dstOP[4];
computeOuterProduct(srcOP, src, srcAve, src, srcAve);
computeOuterProduct(dstOP, src, srcAve, dst, dstAve);
SkScalar det = srcOP[0] * srcOP[3] - srcOP[1] * srcOP[2];
// need SkScalarNearlyZeroSquared for this (to match Chrome's fix)
if (SkScalarNearlyZero(det)) {
return false;
}
SkScalar invDet = SkScalarInvert(det);
// now compute invDet * [srcOP]T * [dstOP]
// scale and transpose
const SkScalar srcOP0 = srcOP[3] * invDet;
const SkScalar srcOP1 = -srcOP[1] * invDet;
const SkScalar srcOP2 = -srcOP[2] * invDet;
const SkScalar srcOP3 = srcOP[0] * invDet;
matrix->reset();
matrix->setScaleX(dot(srcOP0, srcOP1, dstOP[0], dstOP[2]));
matrix->setSkewX( dot(srcOP2, srcOP3, dstOP[0], dstOP[2]));
matrix->setSkewY (dot(srcOP0, srcOP1, dstOP[1], dstOP[3]));
matrix->setScaleY(dot(srcOP2, srcOP3, dstOP[1], dstOP[3]));
matrix->setTranslateX(dstAve.fX - dot(srcAve.fX, srcAve.fY,
matrix->getScaleX(), matrix->getSkewX()));
matrix->setTranslateY(dstAve.fY - dot(srcAve.fX, srcAve.fY,
matrix->getSkewY(), matrix->getScaleY()));
return true;
}
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