/** Now, this is a bit complicated. Once you understand the follwing code, you will
* understand the Tao of SkypeKit video transport.
*/
internal bool GetFrame()
{
// At this point, we already have fresh control struct in our memory.
// This is because we have just called IsNewFrameAvailable and that
// used GetControlData() to fetch in new data.
// The following will deterime, which buffer is available for reading,
// and write the new states back into the control struct. The struct
// will not be sent back to the shared memory until the end of this method.
int bufferState = (controlStruct.bufferstates & 0x03);
if (!haveFrame & bufferState == 0x01) { return false; }
if (!haveFrame) haveFrame = true;
if (bufferState == 0x00) controlStruct.bufferstates |= 0x02;
if (bufferState == 0x03) controlStruct.bufferstates &= ~0x02;
bufferState = (controlStruct.bufferstates & 0x03);
// Now we map ourselves to either buffer1 or buffer2
FrameChannelStruct buffer;
SharedMemoryChannel channel;
if (bufferState == 0x1)
{
buffer = controlStruct.buffer1;
channel = frameChannel1;
}
else if (bufferState == 0x2)
{
buffer = controlStruct.buffer2;
channel = frameChannel2;
}
else throw new Exception("Error: unexpected video control buffer state");
// If there was no frame buffer channel opened for this buffer, we open it.
if (channel == null)
{
channel = new SharedMemoryChannel();
bool success = channel.OpenMapping(buffer.bufid);
if (!success) throw new Exception("Unable to map frame bitmap channel.");
};
// If there was an open channel, we check if the IDs match
if (channel != null)
{
if (channel.key != buffer.bufid)
{
return false;
//throw new Exception("Error: video control buffer ID and frame buffer ID mismatch");
};
};
// Calculating the video frame size
width = buffer.width;
height = buffer.height;
int bytesPerPixel = buffer.bitsperpixel >> 3;
int newFrameSize = width * height * bytesPerPixel;
// If it mismatches with our previous frame size, we need to reallocate buffers.
if (newFrameSize != bitmapDataSize)
{
bitmapData = null;
bitmapDataSize = newFrameSize;
bitmapData = new byte[bitmapDataSize];
}
// And now we marshal the frame into our bitmapData
Marshal.Copy(channel.data, bitmapData, 0, bitmapDataSize);
if (bufferState == 0x1)
{
controlStruct.buffer1 = buffer;
frameChannel1 = channel;
}
else if (bufferState == 0x2)
{
controlStruct.buffer2 = buffer;
frameChannel2 = channel;
}
// And finally, sending the modified control struct back to the shared memory.
// Remember - we modified the buffer states at the behinning of this method.
// We now need to let the other side know that we have finished with current
// buffer and are basically ready for the next one.
SendControlData();
return true;
}
public FrameTransport()
{
sharedInfoSize = (uint)Marshal.SizeOf((Type)typeof(ControlChannelStruct));
haveFrame = false;
bitmapData = null;
bitmapDataSize = 0;
frameChannel1 = null;
frameChannel2 = null;
controlStruct = new ControlChannelStruct();
controlStruct.bufferstates = 1;
controlStruct.buffer1.bufid = -1;
controlStruct.buffer2.bufid = -1;
controlStruct.buffer1.clientpointer = 1;
controlStruct.buffer2.clientpointer = 2;
controlStruct.fourcccount = 0;
controlStruct.buftype = BufferType.WinBuffers;
// Mapping the control channel
controlChannel = new SharedMemoryChannel();
bool success = controlChannel.CreateMapping(sharedInfoSize);
if (!success) throw new Exception("Unable to create memory mapping for video frame transport");
// Opening the control channel for read-write
controlChannel.OpenMapping(controlChannel.key);
int error = Win32.GetLastError();
if (error != 0) throw new Exception("Unable to map memory for video frame transport");
}