move SkPath direction-as-computed into SkPathPriv

src/core/SkPathPriv.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkPathPriv_DEFINED
+#define SkPathPriv_DEFINED
+
+#include "SkPath.h"
+
+class SkPathPriv {
+public:
+    enum FirstDirection {
+        kCW_FirstDirection,         // == SkPath::kCW_Direction

[bsalomon, 2015/06/11 01:37:08]

why not just uncomment this? or static assert?

[robertphillips, 2015/06/15 15:22:35]

I second the static asserts

+        kCCW_FirstDirection,        // == SkPath::kCCW_Direction
+        kUnknown_FirstDirection,
+    };
+
+    static FirstDirection AsFirstDirection(SkPath::Direction dir) {
+        // since we agree numerically for the values in Direction, we can just cast.
+        return (FirstDirection)dir;
+    }
+
+    /**
+     *  Return the opposite of the specified direction. kUnknown is its own
+     *  opposite.
+     */
+    static FirstDirection OppositeFirstDirection(FirstDirection dir) {
+        static const FirstDirection gOppositeDir[] = {
+            kCCW_FirstDirection, kCW_FirstDirection, kUnknown_FirstDirection, 
+        };
+        return gOppositeDir[dir];
+    }
+
+    /**
+     *  Tries to quickly compute the direction of the first non-degenerate
+     *  contour. If it can be computed, return true and set dir to that
+     *  direction. If it cannot be (quickly) determined, return false and ignore
+     *  the dir parameter. If the direction was determined, it is cached to make
+     *  subsequent calls return quickly.
+     */
+    static bool CheapComputeFirstDirection(const SkPath&, FirstDirection* dir);
+
+    /**
+     *  Returns true if the path's direction can be computed via
+     *  cheapComputDirection() and if that computed direction matches the
+     *  specified direction. If dir is kUnknown, returns true if the direction
+     *  cannot be computed.
+     */
+    static bool CheapIsFirstDirection(const SkPath& path, FirstDirection dir) {
+        FirstDirection computedDir = kUnknown_FirstDirection;
+        (void)CheapComputeFirstDirection(path, &computedDir);
+        return computedDir == dir;
+    }
+
+};
+
+#endif