1 files changed, 60 insertions, 0 deletions
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;
+}
+