Fix the rendering error of SkDraw::drawVertices in gpu path for solid color

include/core/SkVertState.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkVertState_DEFINED
+#define SkVertState_DEFINED
+
+#include "SkCanvas.h"
+
+/** \struct VertState
+    It chooses an appropriate function to traverse the vertices according to

[bsalomon, 2014/05/29 18:27:04]

This is a helper for drawVertices(). It is used to iterate over the triangles
that are to be rendered based on an SkCanvas::VertexMode and (optionally) an
index array. It does not copy the index array and the client must ensure it
remains valid for the lifetime of the VertState object.

+    SkCanvas::VertexMode. For example, given vertice indices{0, 1, 2, 3, 4, 5},
+    it returns vertice indices{0, 1, 2; 3, 4, 5} for kTriangles_VertexMode, but
+    returns {0, 1, 2; 0, 2, 3; 0, 3, 4; 0, 4, 5} for kTriangleFan_VertexMode.
+
+    This struct can help to draw the skeleton for a mesh.
+*/
+
+struct VertState {
+    int f0, f1, f2;
+
+    /**
+     *  Pass the indices ptr and index count to construct VertState. Otherwise,

[bsalomon, 2014/05/29 18:27:04]

Construct a VertState from a vertex count, index array, and index count. If the
vertices are unindexed pass NULL for indices.

+     *  Pass the vertex count to the constructor, then the indices will be
+     *  thought as {0, 1, ..., vertex count - 1}.
+     */
+    VertState(int vCount, const uint16_t indices[], int indexCount)
+            : fIndices(indices) {
+        fCurrIndex = 0;
+        if (indices) {
+            fCount = indexCount;
+        } else {
+            fCount = vCount;
+        }
+    }
+
+    typedef bool (*Proc)(VertState*);
+
+    /**
+     *  Choose an appropriate function to traverse the vertices.
+     *  @param mode    Specifies the SkCanvas::VertexMode.
+     */
+    Proc chooseProc(SkCanvas::VertexMode mode);
+
+private:
+    int             fCount;
+    int             fCurrIndex;
+    const uint16_t* fIndices;
+
+    static bool Triangles(VertState*);
+    static bool TrianglesX(VertState*);
+    static bool TriangleStrip(VertState*);
+    static bool TriangleStripX(VertState*);
+    static bool TriangleFan(VertState*);
+    static bool TriangleFanX(VertState*);
+};
+
+#endif