Sketch splitting SkPicture into an interface and SkBigPicture.

src/core/SkMiniRecorder.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 SkMiniRecorder_DEFINED
+#define SkMiniRecorder_DEFINED
+
+#include "SkRecords.h"
+#include "SkScalar.h"
+#include "SkTypes.h"
+class SkCanvas;
+
+// Records small pictures, but only a limited subset of the canvas API, and may fail.
+class SkMiniRecorder : SkNoncopyable {
+public:
+    SkMiniRecorder();
+    ~SkMiniRecorder();
+
+    // Try to record an op.  Returns false on failure.
+    bool drawRect(const SkRect&, const SkPaint&);
+    bool drawPath(const SkPath&, const SkPaint&);
+    bool drawTextBlob(const SkTextBlob*, SkScalar x, SkScalar y, const SkPaint&);
+
+    // Detach anything we've recorded as a picture, resetting this SkMiniRecorder.
+    SkPicture* detachAsPicture(const SkRect& cull);
+
+private:
+    enum class State { kEmpty, kDrawRect, kDrawPath, kDrawTextBlob };
+
+    State fState;
+    SkAlignedSStorage<sizeof(SkRecords::DrawPath)> fBuffer;

[jbroman, 2015/05/07 19:38:25]

Lacking constexpr std::max, maybe a trick like this:

template <typename... Records>
struct MaxSize {};

template <typename Record, typename... Records>
struct MaxSize<Record, Records...> {
  static const size_t value = sizeof(Record) >= MaxSize<Records...>::value ?
sizeof(Record) : MaxSize<Records...>::value;
};

template <>
struct MaxSize<> {
  static const size_t value = 0;
};

SkAlignedSStorage<MaxSize<SkRecords::DrawPath, SkRecords::DrawRect,
SkRecords::DrawTextBlob>::value> fBuffer;

+
+    static_assert(sizeof(SkRecords::DrawRect)     <= sizeof(SkRecords::DrawPath), "");
+    static_assert(sizeof(SkRecords::DrawTextBlob) <= sizeof(SkRecords::DrawPath), "");
+};
+
+#endif//SkMiniRecorder_DEFINED