Checking in filter factory code.

Read the comments in media/base/factory.h for details.

Review URL: http://codereview.chromium.org/17257

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@8071 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 140 insertions, 0 deletions

diff --git a/media/base/factory.h b/media/base/factory.h
new file mode 100644
index 0000000..f735fe1
--- /dev/null
+++ b/media/base/factory.h
@@ -0,0 +1,136 @@
+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// A filter factory handles the creation of filters given a FilterType (i.e.,
+// FILTER_AUDIO_DECODER) and a MediaFormat.  Generally a filter factory handles
+// creating a single type of filter, with multiple factories combined into a
+// FilterFactoryCollection.  We use some template tricks to enforce type-safety
+// and eliminate casting for callers.
+//
+// The majority of applications will only use FilterFactoryCollection since
+// filter factory classes can be created from templates:
+//   FilterFactoryCollection filter_factory = new FilterFactoryCollection();
+//   filter_factory->AddFactory(new TypeFilterFactory<YourAudioDecoder>());
+//   filter_factory->AddFactory(new TypeFilterFactory<YourAudioRenderer>());
+//   etc...
+//   AudioDecoderInterface* filter;
+//   if (filter_factory->Create<AudioDecoderInterface>(media_format, &filter) {
+//     do stuff with the filter...
+//   }
+//
+// The only requirement is that your filter implementation provide a static
+// Create method with the following signature:
+//
+//   Returns true and assigns |filter_out| if the filter was created, false
+//   and assigns NULL otherwise.
+//   static bool Create(MediaFormat* media_format, YourFilterType** filter_out);
+//
+
+#ifndef MEDIA_BASE_FACTORY_H_
+#define MEDIA_BASE_FACTORY_H_
+
+#include <vector>
+
+#include "base/ref_counted.h"
+#include "media/base/filters.h"
+
+namespace media {
+
+class FilterFactoryCollection;
+
+class FilterFactory : base::RefCountedThreadSafe<FilterFactory> {
+ public:
+  // Creates a filter implementing the specified interface.  Hides the casting
+  // and FilterType constants from the callers and produces cleaner code:
+  //   AudioDecoderInterface* filter = NULL;
+  //   bool success = Create<AudioDecoderInterface>(media_format, &filter);
+  template <class T>
+  bool Create(const MediaFormat* media_format, T** filter_out) {
+    return Create(T::kFilterType, media_format,
+                  reinterpret_cast<MediaFilterInterface**>(filter_out));
+  }
+
+ protected:
+  // For accessing the protected version of Create.
+  friend class FilterFactoryCollection;
+
+  // Attempt to create a filter of the given type using the information stored
+  // in |media_format|.  If successful, the filter is assigned to |filter_out|
+  // and the method returns true.  If the filter cannot be created for any
+  // reason, |filter_out| is assigned NULL and false it returned.
+  //
+  // It is assumed that |filter_out| can be safely casted to the corresponding
+  // interface type (i.e., FILTER_AUDIO_DECODER -> AudioDecoderInterface).
+  virtual bool Create(FilterType filter_type, const MediaFormat* media_format,
+                      MediaFilterInterface** filter_out) = 0;
+
+  friend class base::RefCountedThreadSafe<FilterFactory>;
+  virtual ~FilterFactory() {}
+};
+
+
+// Helper template class for implementing trivial filter factories.  If your
+// filter does not require any special handling during creation, you can create
+// a factory for it using this class.  It requires the following static method:
+//   bool Create(MediaFormat* media_format, YourFilterType** filter_out)
+//
+// You can create the filter factory like so:
+//   new TypeFilterFactory<YourFilterType>()
+template <class T>
+class TypeFilterFactory : public FilterFactory {
+ public:
+  TypeFilterFactory() {}
+
+ protected:
+  // Attempts to create a filter of the template type.  Assumes a static method
+  // Create is declared.
+  virtual bool Create(FilterType filter_type, const MediaFormat* media_format,
+                      MediaFilterInterface** filter_out) {
+    T* typed_out;
+    if (T::kFilterType == filter_type && T::Create(media_format, &typed_out)) {
+      *filter_out = typed_out;
+      return true;
+    }
+    return false;
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TypeFilterFactory);
+};
+
+
+// Maintains a collection of FilterFactories.
+class FilterFactoryCollection : public FilterFactory {
+ public:
+  FilterFactoryCollection() {}
+
+  // Adds a factory to the end of the collection.
+  void AddFactory(FilterFactory* factory) {
+    factories_.push_back(factory);
+  }
+
+ protected:
+  // Attempts to create a filter by walking down the list of filter factories.
+  bool Create(FilterType filter_type, const MediaFormat* media_format,
+              MediaFilterInterface** filter_out) {
+    for (FactoryVector::iterator factory = factories_.begin();
+         factory != factories_.end();
+         ++factory) {
+      if ((*factory)->Create(filter_type, media_format, filter_out)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+ private:
+  typedef std::vector< scoped_refptr<FilterFactory> > FactoryVector;
+  FactoryVector factories_;
+
+  DISALLOW_COPY_AND_ASSIGN(FilterFactoryCollection);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_FACTORY_H_
diff --git a/media/build/media.vcproj b/media/build/media.vcproj
index 9b4ad5f..36d944d 100644
--- a/media/build/media.vcproj
+++ b/media/build/media.vcproj
@@ -137,6 +137,10 @@
 				>
 			</File>
 			<File
+				RelativePath="..\base\factory.h"
+				>
+			</File>
+			<File
 				RelativePath="..\base\filter_host.h"
 				>
 			</File>