OpenNI 1.5.4: Capture.cpp file


Capture.cpp file

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  • Capture.cpp

This file contains the code for capturing frames from the OpenNI generator nodes.

Global Type Declarations for Capture.cpp

The Capture.cpp file's global type declarations comprise four type definitions, which are directly connected. The relationship between these four types is presented by by the following summary, with the key components only shown.

            typedef enum { NOT_CAPTURING, ...   } CapturingState;
            typedef enum { CAPTURE_DEPTH_NODE,..., CAPTURE_NODE_COUNT } CaptureNodeType;
            typedef struct NodeCapturingData {  ... } NodeCapturingData;            
            typedef struct CapturingData
                NodeCapturingData nodes[CAPTURE_NODE_COUNT];
                CapturingState State;
            } CapturingData;
            // --------------------------------
            // Global Variables
            // --------------------------------
            CapturingData g_Capture;    

In summary, the major data type is the CapturingData structure, for which a single run-time data instance, g_Capture, is defined, as above, and is used extensively throughout the Capture.cpp module.

As shown above, g_Capture includes the nodes array, containing an entry of type NodeCapturingData for one each of the (four - CAPTURE_NODE_COUNT) types of generator nodes, Depth, Image, IR, and Audio generators. A key data field of NodeCapturingData is pGenerator, for pointing to one of the above generators.

These structures are described separately and in some detail in the subsections further below.

Type definition: CapturingState enum

The CapturingState type is defined as below. It defines a field in the CapturingData structure. It is used as the state controller in the getCaptureMessage() state machine.

                typedef enum
                } CapturingState;

Type definition: CaptureNodeType enum

This type contains enum items for specifying esch of the generator nodes.

                typedef enum
                } CaptureNodeType;

The CaptureNodeType type itself is not currently directly used.

Type definition: NodeCapturingData structure

The NodeCapturingData type is defined as below. It defines a field in the CapturingData structure. It is used as the state controller in the getCaptureMessage() state machine.

                typedef struct NodeCapturingData
                    XnCodecID captureFormat;
                    XnUInt32 nCapturedFrames;
                    bool bRecording;
                    xn::Generator* pGenerator;
                } NodeCapturingData;

captureFormat: For containing the current codec enum ID of a generator node. Note that later in this file (in Function: captureInit() - Initializes the Primary Stream and the Resolutions) all of the codec text names and enum IDs for each node type area stored (in g_DepthFormat.pValues[] and g_DepthFormat.pIndexToName[nIndex]).

Type definition: CapturingData struct

                typedef struct CapturingData
                    NodeCapturingData nodes[CAPTURE_NODE_COUNT];
                    Recorder* pRecorder;
                    char csFileName[XN_FILE_MAX_PATH];
                    XnUInt32 nStartOn; // time to start, in seconds
                    bool bSkipFirstFrame;
                    CapturingState State;
                    XnUInt32 nCapturedFrameUniqueID;
                    char csDisplayMessage[500];
                } CapturingData;            

Global Variable Declarations for Capture.cpp

The Capture.cpp file's global variable declarations includes the central g_Capture variable and a format variable of NodeCodec type for each of the four generator nodes - see the declaration block below. NodeCodec is defined in Device.h. It contains codec definitions for all the codecs of each generator node.

            // --------------------------------
            // Global Variables
            // --------------------------------
            CapturingData g_Capture;

            NodeCodec g_DepthFormat;
            NodeCodec g_ImageFormat;
            NodeCodec g_IRFormat;
            NodeCodec g_AudioFormat;

Function: captureInit() - Initializes the Primary Stream and the Resolutions

This function initializes the main g_Capture variable and the NodeCodec structures, for example, g_DepthFormat.

Following are examples of NodeCodec structures. Note that for each Generator node there can be a number of codes defined. For example, in the code sample below, for the DepthGenerator node there are defined the codecs XN_CODEC_16Z_EMB_TABLES and XN_CODEC_UNCOMPRESSED.

            void captureInit()
                // Depth Formats
                int nIndex = 0;

                g_DepthFormat.pValues[nIndex] = XN_CODEC_16Z_EMB_TABLES;
                g_DepthFormat.pIndexToName[nIndex] = "PS Compression (16z ET)";

                g_DepthFormat.pValues[nIndex] = XN_CODEC_UNCOMPRESSED;
                g_DepthFormat.pIndexToName[nIndex] = "Uncompressed";

Each entry in the g_DepthFormat.pValues[] array specifies a codec ID, e.g., xn::XN_CODEC_16Z_EMB_TABLES. Each entry in the g_DepthFormat.pIndexToName[] array specifies a human readable text name for the codec, e.g., "<code>PS Compression (16z ET)</code>".

The g_Capture data structure variable is initialized as follows.

            g_Capture.csFileName[0] = 0;
            g_Capture.State = NOT_CAPTURING;
            g_Capture.nCapturedFrameUniqueID = 0;
            g_Capture.csDisplayMessage[0] = '\0';
            g_Capture.bSkipFirstFrame = false;

            g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat = XN_CODEC_16Z_EMB_TABLES;
            g_Capture.nodes[CAPTURE_IMAGE_NODE].captureFormat = XN_CODEC_JPEG;
            g_Capture.nodes[CAPTURE_IR_NODE].captureFormat = XN_CODEC_UNCOMPRESSED;
            g_Capture.nodes[CAPTURE_AUDIO_NODE].captureFormat = XN_CODEC_UNCOMPRESSED;

Note in the above initializations:

  • Capture State -- in g_Capture.State -- is initialized to NOT_CAPTURING.
  • g_Capture.nodes[] is a list of captureFormat structures and it is initialized to contain the current codecs to be used for each Generator node. Note that earlier in this function all of the codecs for each node type have been stored in g_DepthFormat.pValues[] and g_DepthFormat.pIndexToName[nIndex].

Function: isCapturing() - Are the Generator nodes in Capturing State

Returns whther the generator nodes are currently attempting to capture frames.

            bool isCapturing()
                return (g_Capture.State != NOT_CAPTURING);

Function: captureOpenWriteDevice() - Open a Write Device

The following code block calls EnumerateProductionTrees to list all available Recorder production nodes and returns a full list of the matching production nodes. The chosen pointer picks the first in the list, and to select the NodeInfo information of a Recorder node for recording a data generation session.

            NodeInfoList recordersList;
            nRetVal = g_Context.EnumerateProductionTrees(XN_NODE_TYPE_RECORDER, NULL, recordersList);
            NodeInfo chosen = *recordersList.Begin();

The following code block creates a production graph for the selected Recorder node. A pointer to the Recorder is held to the g_Capture variable.

            g_Capture.pRecorder = new Recorder;
            nRetVal = g_Context.CreateProductionTree(chosen, *g_Capture.pRecorder);
            START_CAPTURE_CHECK_RC(nRetVal, "Create recorder");

Finally, the destnation file or the recording is set, as follows.

            nRetVal = g_Capture.pRecorder->SetDestination(XN_RECORD_MEDIUM_FILE, g_Capture.csFileName);         

Function: captureBrowse() - Opens a Write Device

This function opens the write device.

as we waited for user input, it's probably better to discard first frame (especially if an accumulating stream is on, like audio).

Function: captureStart() - Starts the Capturing Process

This function starts capturing process. The important features are that it sets the tiem for starting capturing by assigning the current time to g_Capture weit an added delay; and then it sets the Capture state to SHOULD_CAPTURE, indicating taht a future time has been set for starting capturing. This is shown below.

            XnUInt64 nNow;
            nNow /= 1000;
            g_Capture.nStartOn = (XnUInt32)nNow + nDelay;
            g_Capture.State = SHOULD_CAPTURE;

Function: captureCloseWriteDevice() - Closes a Write Device

This function closes a write device. Among the 'close' operations, it calls Release() to Unreference a production node. This decreases its reference count by 1. If the reference count reaches zero, the node will be destroyed.

            if (g_Capture.pRecorder != NULL)
                delete g_Capture.pRecorder;
                g_Capture.pRecorder = NULL;

Function: captureRestart() - Restarts the Recording Process

This function restarts the recording module. It simply uses the captureCloseWriteDevice() defined just above to close the recording device. This function then reopens the recording module by using the captureOpenWriteDevice() defined further above. g_Capture.State remains at it current state.

Function: captureStop() - Stops the Recording Process

This function stops the recording module, i.e., it puts it into NOT_CAPTURING state. Thus, for this purpose CAPTURING state and SHOULD_CAPTURE state are both defined as 'capturing state'. This function simply uses the captureCloseWriteDevice() defined just above to close the recording device.

Function: captureFrame() - Main State Machine for Capturing Frames from Generator Nodes

This function is the main state machine for capturing frames from generator nodes. This function processes two states: CAPTURING state and SHOULD_CAPTURE state.


In this state, this function add nodes to the recording.

This function first checks if the capture time has been reached. (This time delay was set in the captureStart() function.)

                if (g_Capture.State == SHOULD_CAPTURE)
                    XnUInt64 nNow;
                    nNow /= 1000;

                    // check if time has arrived
                    if (nNow >= g_Capture.nStartOn)         

Once the capture time and started and this function starts to capture, it performs some initialization and sets the Capturing state to CAPTURING state.

                g_Capture.State = CAPTURING;

The following 'if' statement adds a valid device node to the recorder. This is for recording raw input data from the device.

                if (getDevice() != NULL)
                    nRetVal = g_Capture.pRecorder->AddNodeToRecording(*getDevice(), XN_CODEC_UNCOMPRESSED);
                    START_CAPTURE_CHECK_RC(nRetVal, "add device node");

The xn::Recorder::AddNodeToRecording() adds a node to the recording setup, and starts recording data that the node generates. This method must be called for each node to be recorded with this recorder. The call passes as parameters a pointer to the node and the enum ID of the codec to be used.

The following sequence of 'if' statements adds nodes to the recorder. A node is added to the recorder only if:

  • the node is 'On' (e.g., g_bIsDepthOn=true for a DepthGenerator node), and
  • the node's captureFormat is defined (i.e., captureFormat!= CODEC_DONT_CAPTURE As an example, the following code block shows the code for the DepthGenerator node.
                    if (isDepthOn() && (g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat != CODEC_DONT_CAPTURE))
                        nRetVal = g_Capture.pRecorder->AddNodeToRecording(*getDepthGenerator(), g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat);
                        START_CAPTURE_CHECK_RC(nRetVal, "add depth node");
                        g_Capture.nodes[CAPTURE_DEPTH_NODE].bRecording = TRUE;
                        g_Capture.nodes[CAPTURE_DEPTH_NODE].pGenerator = getDepthGenerator();

In the above, the code saves in g_Capture a pointer to the DepthGenerator node by assigning the return result of getDepthGenerator().


In this state, this function starts recording data generated from the nodes.

Once all required nodes are added, the application can read data from the nodes and record it. Recording of data can be achieved either by explicitly calling the xn::Recorder::Record() method, or by using one of the 'Update All' functions. This function demonstrates using the Record() method.

                if (g_Capture.State == CAPTURING)
                    nRetVal = g_Capture.pRecorder->Record();

There isn't a real need to call Record() here, as the WaitXUpdateAll() call from IdleCallback() in the NiView.cpp file already makes sure that recording is performed.

The following loop counts recorded frames. It uses the xn::Generator::IsDataNew() method to test of a generate nodfe has actually generated new data. the IsDataNew() method returns whether the node's frame data was updated by the most recent call to any 'WaitXUpdateAll' function (e.g., xn::Context::WaitAndUpdateAll()).

                for (int i = 0; i < CAPTURE_NODE_COUNT; ++i)
                    if (g_Capture.nodes[i].bRecording && g_Capture.nodes[i].pGenerator->IsDataNew())

Function: captureSetFormat() - Selects a New Codec for Recording

This function is used by a number of individual 'Set Format' functions (e.g., captureSetDepthFormat() - described further below) to select a new codec for recording.


pMember: the old format
newFormat: the new format
node: ProductionNode specifier

If a state change is being requested, i.e., from 'not capture' to 'capture', or the reverse, then the node is added to or removed from the Recorder, accordingly.

If a codec change is being requested, then the node removed from the Recorder and then added again, this time with the new codec.

Function group: 'Set Format' for each Production Node

All functions in this group call the captureSetFormat() described above. For example:

            void captureSetDepthFormat(int format)
                captureSetFormat(&g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat, format, *getDepthGenerator());

Function: getCodecName() - Gets Text Name of Node's Current Codec

This function gets the text name of the current codec being used for a specific node.

This function is used by a number of individual 'GetDepthFormatName' functions (e.g., captureGetImageFormatName() - described further below) to get the text name of a specified codec from the list of all possible codecs for a specific node.


pNodeCodec: a specific generator node's list of all codec ID info (text name and ID enum), e.g., this function is called with g_DepthFormat passed as this parameter

codecID: the enum ID of the codec currently being used for the specific generator node

            for (int i = 0; i < pNodeCodec->nValuesCount; i++)
                if (pNodeCodec->pValues[i] == codecID)
                    return pNodeCodec->pIndexToName[i];

Function group: 'getCodecName' for each Generator node

All functions in this group call the getCodecName() described above. For example:

            const char* captureGetDepthFormatName()
                return getCodecName(&g_DepthFormat, g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat);

Function: 'getCaptureMessage()'

This function builds a capture message according to the current Capture State.

In this function, there is one OpenNI method of note - the xn::NodeWrapper::GetName() method - see the 'case' block below.

            case CAPTURING:
                int nChars = sprintf(pMessage, "* Recording! Press any key or use menu to stop *\nRecorded Frames: ");
                for (int i = 0; i < CAPTURE_NODE_COUNT; ++i)
                    if (g_Capture.nodes[i].bRecording)
                        nChars += sprintf(pMessage + nChars, "%s-%d ", g_Capture.nodes[i].pGenerator->GetName(), g_Capture.nodes[i].nCapturedFrames);

The GetName() method gets the instance name of a node. Unless the application made a specific request for a specific name, the name will be of the form: "Depth1", "Image2", etc.

GetName() is a member of the NodeWrapper class. The NodeWrapper class is the base class for all OpenNI node classes in C++, for example, the xn::ProductionNode class and the xn::Generator class.

Function group: 'Get File Name' - Build a file name for each Generator node

All functions in this group build a file name (from a path and ID number) for saving a captured data frame. For example:

            const char* captureGetDepthFormatName()
                return getCodecName(&g_DepthFormat, g_Capture.nodes[CAPTURE_DEPTH_NODE].captureFormat);

This unique file name is later to save a captured data frame to a file for storage.

All the functions in this group are called from the findUniqueFileName() function (described immediately below)

Function: findUniqueFileName() - Builds a Unique File Name for Saving a Captured Data Frame

This function builds a unique file name for saving a captured data frame.

The purpose of this function is straightforward and there are no OpenNI specific operations in this function.

Function: captureSingleFrame() - Captures a Single Frame

This function captures a single data frame from each generator node.

The function first builds for each generator node a unique file name for saving the data frame.

Then the function gets a frame object for each generator node. A "frame object" is a data frame and associated configuration information saved from a generator node. For example,

            const ImageMetaData* pImageMD = getImageMetaData();
            if (pImageMD != NULL)
                xnOSSaveFile(csImageFileName, pImageMD->Data(), pImageMD->DataSize());

In this sample program, the frame objects are stored as metadata objects in the readFrame() function in the Device.cpp file of this program sample. getImageMetaData() is also a function in this sample program for simply getting the frame object that was already saved.

Generated on Wed May 16 2012 10:16:06 for OpenNI 1.5.4 by   doxygen