Simplify flattening to just write enough to call the factory

include/core/SkImageFilter.h

Index: include/core/SkImageFilter.h
diff --git a/include/core/SkImageFilter.h b/include/core/SkImageFilter.h
index d4930c4975935801a26b2e03fd59da3cdb3b62f8..94894514df9cdb66988cce310c603bf658ec2fcc 100644
--- a/include/core/SkImageFilter.h
+++ b/include/core/SkImageFilter.h
@@ -205,13 +205,23 @@ protected:
         Common() {}
         ~Common();
 
+        /**
+         *  Attempt to unflatten the cropRect and the expected number of input filters.
+         *  If any number of input filters is valid, pass -1.
+         *  If this fails (i.e. corrupt buffer or contents) then return false and common will
+         *  be left uninitialized.
+         *  If this returns true, then inputCount() is the number of found input filters, each
+         *  of which may be NULL or a valid imagefilter.
+         */
         bool unflatten(SkReadBuffer&, int expectedInputs = -1);
 
-        CropRect        cropRect() const { return fCropRect; }
+        const CropRect& cropRect() const { return fCropRect; }
         int             inputCount() const { return fInputs.count(); }
         SkImageFilter** inputs() const { return fInputs.get(); }
         uint32_t        uniqueID() const { return fUniqueID; }
 
+        SkImageFilter*  inputAt(int index) const { return fInputs[index]; }
+
         // If the caller wants a copy of the inputs, call this and it will transfer ownership
         // of the unflattened input filters to the caller. This is just a short-cut for copying
         // the inputs, calling ref() on each, and then waiting for Common's destructor to call
@@ -240,7 +250,7 @@ protected:
      */
     explicit SkImageFilter(int inputCount, SkReadBuffer& rb);
 
-    virtual void flatten(SkWriteBuffer& wb) const SK_OVERRIDE;
+    virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
     /**
      *  This is the virtual which should be overridden by the derived class
@@ -320,4 +330,15 @@ private:
     uint32_t fUniqueID; // Globally unique
 };
 
+/**
+ *  Helper to unflatten the common data, and return NULL if we fail.
+ */
+#define SK_IMAGEFILTER_UNFLATTEN_COMMON(localVar, expectedCount)    \
+    Common localVar;                                                \
+    do {                                                            \
+        if (!localVar.unflatten(buffer, expectedCount)) {           \
+            return NULL;                                            \
+        }                                                           \
+    } while (0)

[sugoi1, 2014/08/19 18:46:16]

I understand the use of do { ... } while(0) by itself in a macro, but since you
also have "Common localVar;" at the beginning of this macro, I don't think this
would allow you to do more than just a regular scope { }, since writing
something like:

if (condition)
  SK_IMAGEFILTER_UNFLATTEN_COMMON(...);
else

would fail anyway. Maybe there's another reason for using "do { ... } while(0)"
that you know.

[reed1, 2014/08/19 19:58:05]

True, the presence of the localVar may obviate the need for the do/while.

+
 #endif