add SkMatrixPriv for specialized helpers

src/core/SkMatrixPriv.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkMatrixPriv_DEFINE
+#define SkMatrixPriv_DEFINE
+
+#include "SkMatrix.h"
+#include "SkNx.h"
+
+class SkMatrixPriv {
+public:
+    /**
+     *  Attempt to map the rect through the inverse of the matrix. If it is not invertible,
+     *  then this returns false and dst is unchanged.
+     */
+    static bool SK_WARN_UNUSED_RESULT InverseMapRect(const SkMatrix& mx,
+                                                     SkRect* dst, const SkRect& src) {
+        if (mx.getType() <= SkMatrix::kTranslate_Mask) {
+            SkScalar tx = mx.getTranslateX();
+            SkScalar ty = mx.getTranslateY();
+            Sk4f trans(tx, ty, tx, ty);
+            (Sk4f::Load(&src.fLeft) - trans).store(&dst->fLeft);
+            return true;
+        }
+        // Insert other special-cases here (e.g. scale+translate)
+        
+        // general case
+        SkMatrix inverse;
+        if (mx.invert(&inverse)) {
+            inverse.mapRect(dst, src);
+            return true;
+        }
+        return false;
+    }
+
+    static void MapPointsWithStride(const SkMatrix& mx, SkPoint pts[], size_t stride, int count) {
+        SkASSERT(stride >= sizeof(SkPoint));
+        SkASSERT(0 == stride % sizeof(SkScalar));
+
+        SkMatrix::TypeMask tm = mx.getType();
+        
+        if (SkMatrix::kIdentity_Mask == tm) {
+            return;
+        }
+        if (SkMatrix::kTranslate_Mask == tm) {
+            const SkScalar tx = mx.getTranslateX();
+            const SkScalar ty = mx.getTranslateY();
+            Sk2s trans(tx, ty);
+            for (int i = 0; i < count; ++i) {
+                (Sk2s::Load(&pts->fX) + trans).store(&pts->fX);
+                pts = (SkPoint*)((intptr_t)pts + stride);
+            }
+            return;
+        }
+        // Insert other special-cases here (e.g. scale+translate)
+        
+        // general case
+        SkMatrix::MapXYProc proc = mx.getMapXYProc();
+        for (int i = 0; i < count; ++i) {
+            proc(mx, pts->fX, pts->fY, pts);
+            pts = (SkPoint*)((intptr_t)pts + stride);
+        }
+    }
+};
+
+#endif