Implement device enumeration for PPB_VideoCapture_Dev.

ppapi/cpp/dev/video_capture_dev.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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.
 
 #ifndef PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_
 #define PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_
 
+#include <vector>
+
 #include "ppapi/c/dev/pp_video_capture_dev.h"
 #include "ppapi/cpp/resource.h"
 
 namespace pp {
 
+class CompletionCallback;
+class DeviceRef_Dev;
 class Instance;
 
 class VideoCapture_Dev : public Resource {
  public:
   explicit VideoCapture_Dev(const Instance& instance);
   VideoCapture_Dev(PP_Resource resource);
   VideoCapture_Dev(const VideoCapture_Dev& other);
 
   // Returns true if the required interface is available.
   static bool IsAvailable();
 
-  int32_t StartCapture(const PP_VideoCaptureDeviceInfo_Dev& requested_info,
+  int32_t EnumerateDevices(const CompletionCallback& callback);
+  void GetDevices(std::vector<DeviceRef_Dev>* devices);

[brettw, 2012/02/06 21:51:52]

My previous suggestion about combining these two functions opens up some
questions about what to do here. If we want to keep returning a std::vector<>, I
think we'll need to have a wrapper completion callback.

I just tried to write such a wrapper to see how it would work, and it came out
excessively complicated. For now, let's just use a PP_Resource* out param and
force the caller to handle this (it should be straightforward). We can enhance
the wrapper in the future if think it would be helpful.

[yzshen1, 2012/02/06 22:42:56]

Do you mean you was trying to write a completion callback wrapper that will have
more flexible input parameters, such as
    void callback_func(int32_t result, const std::vector<DeviceRef_Dev>&
devices)?

Comparing with a raw PP_Resource* out param, how about
int32_t EnumerateDevices(std::vector<DeviceRef_Dev>* devices, const
CompletionCallback& callback)?

[yzshen1, 2012/02/10 07:10:44]

I finally decided to write into a std::vector<> out param, and make sure that we
don't write into it once the VideoCapture_Dev object dies. This is easier for
plugin developers.

It looks a little bit messy. As we discussed, I think in the future we could
extend CompletionCallback&CallbackFactory to handle the ownership of out params.

On 2012/02/06 21:51:52, brettw wrote:

+  // If |device_ref| is null (i.e., is_null() returns true), the default device
+  // will be used.
+  int32_t StartCapture(const DeviceRef_Dev& device_ref,
+                       const PP_VideoCaptureDeviceInfo_Dev& requested_info,
                        uint32_t buffer_count);
   int32_t ReuseBuffer(uint32_t buffer);
   int32_t StopCapture();
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_VIDEO_CAPTURE_DEV_H_