Simplify flattening to just write enough to call the factory

include/core/SkFlattenable.h

-
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-
 #ifndef SkFlattenable_DEFINED
 #define SkFlattenable_DEFINED
 
 #include "SkRefCnt.h"
 
 class SkReadBuffer;
 class SkWriteBuffer;
 
-#define SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(flattenable) \
-        SkFlattenable::Registrar(#flattenable, flattenable::CreateProc, \
-                                 flattenable::GetFlattenableType());
+#define SK_SUPPORT_LEGACY_DEEPFLATTENING
+
+/*
+ *  Flattening is straight-forward:
+ *      1. call getFactory() so we have a function-ptr to recreate the subclass
+ *      2. call flatten(buffer) to write out enough data for the factory to read
+ *
+ *  Unflattening is easy for the caller: new_instance = factory(buffer)
+ *
+ *  The complexity of supporting this is as follows.
+ *
+ *  If your subclass wants to control unflattening, use this macro in your declaration:
+ *      SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS
+ *  This will provide a getFactory(), and require that the subclass implements CreateProc.
+ *
+ *  For older buffers (before the DEEPFLATTENING change, the macros below declare
+ *  a thin factory DeepCreateProc. It checks the version of the buffer, and if it is pre-deep,
+ *  then it calls through to a (usually protected) constructor, passing the buffer.
+ *  If the buffer is newer, then it directly calls the "real" factory: CreateProc.
+ */
 
 #define SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP() static void InitializeFlattenables();
 
 #define SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(flattenable) \
     void flattenable::InitializeFlattenables() {
 
 #define SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END \
     }
 
 #define SK_DECLARE_UNFLATTENABLE_OBJECT() \
     virtual Factory getFactory() const SK_OVERRIDE { return NULL; }
 
-#define SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(flattenable) \
-    virtual Factory getFactory() const SK_OVERRIDE { return CreateProc; } \
-    static SkFlattenable* CreateProc(SkReadBuffer& buffer) { \
-        return SkNEW_ARGS(flattenable, (buffer)); \
-    }
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+#define SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(flattenable) \
+    SkFlattenable::Registrar(#flattenable, flattenable::DeepCreateProc, \
+                             flattenable::GetFlattenableType());
+
+#define SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(flattenable)    \
+    private:                                                                \
+    static SkFlattenable* CreateProc(SkReadBuffer&);                        \
+    static SkFlattenable* DeepCreateProc(SkReadBuffer& buffer) {            \
+        if (NeedsDeepUnflatten(buffer)) {                                   \
+            return SkNEW_ARGS(flattenable, (buffer));                       \
+        }                                                                   \
+        return CreateProc(buffer);                                          \
+    }                                                                       \
+    friend class SkPrivateEffectInitializer;                                \
+    public:                                                                 \
+    virtual Factory getFactory() const SK_OVERRIDE {return DeepCreateProc;}
+#else
+#define SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(flattenable) \
+    SkFlattenable::Registrar(#flattenable, flattenable::CreateProc, \
+                             flattenable::GetFlattenableType());
+
+#define SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(flattenable)    \
+    private:                                                                \
+    static SkFlattenable* CreateProc(SkReadBuffer&);                        \
+    friend class SkPrivateEffectInitializer;                                \
+    public:                                                                 \
+    virtual Factory getFactory() const SK_OVERRIDE { return CreateProc; }
+#endif
+
+// If your subclass will *never* need to be unflattened, declare this.
+#define SK_DECLARE_NOT_FLATTENABLE_PROCS(flattenable)   \
+    virtual Factory getFactory() const SK_OVERRIDE { return ReturnNullCreateProc; }
 
 /** For SkFlattenable derived objects with a valid type
     This macro should only be used in base class objects in core
   */
 #define SK_DEFINE_FLATTENABLE_TYPE(flattenable) \
     static Type GetFlattenableType() { \
         return k##flattenable##_Type; \
     }
 
 /** \class SkFlattenable
@@ skipping 39 matching lines @@
 
     static void Register(const char name[], Factory, Type);
 
     class Registrar {
     public:
         Registrar(const char name[], Factory factory, Type type) {
             SkFlattenable::Register(name, factory, type);
         }
     };
 
-    /** Override this to write data specific to your subclass into the buffer,
-     being sure to call your super-class' version first. This data will later
-     be passed to your Factory function, returned by getFactory().
+    /**
+     *  Override this if your subclass needs to record data that it will need to recreate itself
+     *  from its CreateProc (returned by getFactory()).
      */
-    virtual void flatten(SkWriteBuffer&) const;
+    virtual void flatten(SkWriteBuffer&) const {}
 
 protected:
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+    static bool NeedsDeepUnflatten(const SkReadBuffer&);
     SkFlattenable(SkReadBuffer&) {}
+#endif
+
+    static SkFlattenable* ReturnNullCreateProc(SkReadBuffer&) {
+        return NULL;
+    }
 
 private:
     static void InitializeFlattenablesIfNeeded();
 
     friend class SkGraphics;
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif