grab from latest android
git-svn-id: http://skia.googlecode.com/svn/trunk@27 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/experimental/SkSetPoly3To3.cpp b/experimental/SkSetPoly3To3.cpp
new file mode 100644
index 0000000..1420eba
--- /dev/null
+++ b/experimental/SkSetPoly3To3.cpp
@@ -0,0 +1,60 @@
+#include "SkMatrix.h"
+
+static void computeOuterProduct(SkScalar op[4],
+ const SkPoint pts0[3], const SkPoint& ave0,
+ const SkPoint pts1[3], const SkPoint& ave1) {
+ 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] += SkScalarMul(x0, x1);
+ op[1] += SkScalarMul(x0, y1);
+ op[2] += SkScalarMul(y0, x1);
+ op[3] += SkScalarMul(y0, y1);
+ }
+}
+
+static SkScalar dot(SkScalar ax, SkScalar ay, SkScalar bx, SkScalar by) {
+ return SkScalarMul(ax, bx) + SkScalarMul(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 = SkScalarMul(srcOP[0], srcOP[3]) - SkScalarMul(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 = SkScalarMul( srcOP[3], invDet);
+ const SkScalar srcOP1 = SkScalarMul(-srcOP[1], invDet);
+ const SkScalar srcOP2 = SkScalarMul(-srcOP[2], invDet);
+ const SkScalar srcOP3 = SkScalarMul( 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;
+}
+