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// Copyright (c) 2006-2009 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...
// AudioDecoder* filter;
// if (filter_factory->Create<AudioDecoder>(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 : public base::RefCountedThreadSafe<FilterFactory> {
public:
// Creates a filter implementing the specified interface. Hides the casting
// and FilterType constants from the callers and produces cleaner code:
// socped_refptr<MyAudioDecoder> d = Create<MyAudioDecoder>(media_format);
// If the factory does not support the specific filter type or does not
// support the |media_format| then NULL is returned.
template <class Filter>
Filter* Create(const MediaFormat* media_format) {
return reinterpret_cast<Filter*>(Create(Filter::filter_type(),
media_format));
}
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 returned. If the filter
// cannot be created for any reason, NULL is returned.
//
// It is assumed that the MediaFilter interface can be safely cast to the
// corresponding interface type (i.e., FILTER_AUDIO_DECODER -> AudioDecoder).
virtual MediaFilter* Create(FilterType filter_type,
const MediaFormat* media_format) = 0;
friend class base::RefCountedThreadSafe<FilterFactory>;
virtual ~FilterFactory() {}
};
// 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.
MediaFilter* Create(FilterType filter_type, const MediaFormat* media_format) {
MediaFilter* filter = NULL;
for (FactoryVector::iterator factory = factories_.begin();
!filter && factory != factories_.end();
++factory) {
filter = (*factory)->Create(filter_type, media_format);
}
return filter;
}
private:
typedef std::vector< scoped_refptr<FilterFactory> > FactoryVector;
FactoryVector factories_;
DISALLOW_COPY_AND_ASSIGN(FilterFactoryCollection);
};
//-----------------------------------------------------------------------------
// This template is used by classes to implement a type-safe filter factory.
// If the derived class needs to examine the |media_format| passed to the
// Create method then they should implement the static method
// IsMediaFormatSupported. Classes should implement their contructor as private
// and make FilterFactoryImpl<MyClass> a friend class.
template <class Filter>
class FilterFactoryImpl0 : public FilterFactory {
public:
FilterFactoryImpl0() {}
protected:
virtual MediaFilter* Create(FilterType filter_type,
const MediaFormat* media_format) {
Filter* filter = NULL;
if (Filter::filter_type() == filter_type &&
Filter::IsMediaFormatSupported(media_format)) {
filter = new Filter();
}
return filter;
}
private:
DISALLOW_COPY_AND_ASSIGN(FilterFactoryImpl0);
};
// This template can be used by classes that need to be constructed with a
// parameter that needs to be used in the construction of the actual filter.
// This would usually be a "parent" object which the instantiated filter needs
// to communicate with. The class's CreateFactory method would look like:
// static FilterFactory* CreateFactory(MyRequiredParentClass* parent) {
// return new FilterFactoryImpl1<MyClass>(parent);
// }
// The class would be constructed with the same pointer passed to the
// CreateFactory method.
template <class Filter, class A>
class FilterFactoryImpl1 : public FilterFactory {
public:
explicit FilterFactoryImpl1(A a) : a_(a) {}
protected:
virtual MediaFilter* Create(FilterType filter_type,
const MediaFormat* media_format) {
Filter* filter = NULL;
if (Filter::filter_type() == filter_type &&
Filter::IsMediaFormatSupported(media_format)) {
filter = new Filter(a_);
}
return filter;
}
private:
A const a_;
DISALLOW_COPY_AND_ASSIGN(FilterFactoryImpl1);
};
//------------------------------------------------------------------------------
// This specialized factory is typically used by test programs that create
// a filter instance, and want to return that specific instance of the test
// filter to the pipeline. It takes an already created filter in the
// constructor, and then hands that instance out when the Create method is
// called. The factory makes sure to only return a single copy of the
// filter. The normal patern of use for this factory is:
// scoped_refptr<MyTestFilter> my_test_filter = new MyTestFilter();
// filter_factory_collection->AddFactory(
// new InstanceFilterFactory<MyTestFilter>(my_test_filter));
template <class Filter>
class InstanceFilterFactory : public FilterFactory {
public:
explicit InstanceFilterFactory(Filter* filter)
: filter_(filter),
create_called_(false) {
}
protected:
virtual MediaFilter* Create(FilterType filter_type,
const MediaFormat* media_format) {
if (Filter::filter_type() == filter_type &&
Filter::IsMediaFormatSupported(media_format)) {
if (!create_called_) {
create_called_ = true;
return filter_;
} else {
NOTREACHED();
}
}
return NULL;
}
private:
scoped_refptr<Filter> filter_;
bool create_called_;
DISALLOW_COPY_AND_ASSIGN(InstanceFilterFactory);
};
} // namespace media
#endif // MEDIA_BASE_FACTORY_H_
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