v4l/libv4l: allow opening device by name

- Allows using non-default device names such as /dev/v4l/by-path/pci-0000:00:1d.0-usb-0:1.1:1.0-video-index0

modules/videoio/src/cap.cpp

@@ -292,6 +292,11 @@ CV_IMPL CvCapture * cvCreateFileCaptureWithPreference (const char * filename, in
             result = cvCreateFileCapture_VFW (filename);
         if (apiPreference) break;
 #endif
+#if defined HAVE_LIBV4L || defined HAVE_CAMV4L || defined HAVE_CAMV4L2 || defined HAVE_VIDEOIO
+        if (!result)
+            result = cvCreateCameraCapture_V4L(filename);
+        if (apiPreference) break;
+#endif
 
     case CV_CAP_MSMF:
 #ifdef HAVE_MSMF

modules/videoio/src/cap_libv4l.cpp

@@ -350,6 +350,7 @@ typedef struct CvCaptureCAM_V4L
 }
 CvCaptureCAM_V4L;
 
+static CvCaptureCAM_V4L * icvCaptureFromCAM_V4L (const char* deviceName);
 static void icvCloseCAM_V4L( CvCaptureCAM_V4L* capture );
 
 static int icvGrabFrameCAM_V4L( CvCaptureCAM_V4L* capture );
@@ -416,7 +417,7 @@ static void icvInitCapture_V4L() {
 }; /* End icvInitCapture_V4L */
 
 
-static int try_init_v4l(CvCaptureCAM_V4L* capture, char *deviceName)
+static int try_init_v4l(CvCaptureCAM_V4L* capture, const char *deviceName)
 
 {
 
@@ -460,7 +461,7 @@ static int try_init_v4l(CvCaptureCAM_V4L* capture, char *deviceName)
 }
 
 
-static int try_init_v4l2(CvCaptureCAM_V4L* capture, char *deviceName)
+static int try_init_v4l2(CvCaptureCAM_V4L* capture, const char *deviceName)
 {
 
   // if detect = -1 then unable to open device
@@ -662,7 +663,7 @@ static inline int channels_for_mode(int mode)
     }
 }
 
-static int _capture_V4L2 (CvCaptureCAM_V4L *capture, char *deviceName)
+static int _capture_V4L2 (CvCaptureCAM_V4L *capture, const char *deviceName)
 {
    int detect_v4l2 = 0;
 
@@ -870,7 +871,7 @@ static int _capture_V4L2 (CvCaptureCAM_V4L *capture, char *deviceName)
 }; /* End _capture_V4L2 */
 
 
-static int _capture_V4L (CvCaptureCAM_V4L *capture, char *deviceName)
+static int _capture_V4L (CvCaptureCAM_V4L *capture, const char *deviceName)
 {
    int detect_v4l = 0;
 
@@ -1041,17 +1042,6 @@ static CvCaptureCAM_V4L * icvCaptureFromCAM_V4L (int index)
      fprintf( stderr, "VIDEOIO ERROR: V4L: index %d is not correct!\n",index);
      return NULL; /* Did someone ask for not correct video source number? */
    }
-   /* Allocate memory for this humongus CvCaptureCAM_V4L structure that contains ALL
-      the handles for V4L processing */
-   CvCaptureCAM_V4L * capture = (CvCaptureCAM_V4L*)cvAlloc(sizeof(CvCaptureCAM_V4L));
-   if (!capture) {
-      fprintf( stderr, "VIDEOIO ERROR: V4L: Could not allocate memory for capture process.\n");
-      return NULL;
-   }
-
-#ifdef USE_TEMP_BUFFER
-   capture->buffers[MAX_V4L_BUFFERS].start = NULL;
-#endif
 
    /* Select camera, or rather, V4L video source */
    if (index<0) { // Asking for the first device available
@@ -1065,9 +1055,26 @@ static CvCaptureCAM_V4L * icvCaptureFromCAM_V4L (int index)
    }
    /* Print the CameraNumber at the end of the string with a width of one character */
    sprintf(deviceName, "/dev/video%1d", index);
+   return icvCaptureFromCAM_V4L(deviceName);
+}
+
+static CvCaptureCAM_V4L * icvCaptureFromCAM_V4L (const char* deviceName)
+{
+   /* Allocate memory for this humongus CvCaptureCAM_V4L structure that contains ALL
+      the handles for V4L processing */
+   CvCaptureCAM_V4L * capture = (CvCaptureCAM_V4L*)cvAlloc(sizeof(CvCaptureCAM_V4L));
+   if (!capture) {
+      fprintf( stderr, "VIDEOIO ERROR: V4L: Could not allocate memory for capture process.\n");
+      return NULL;
+   }
+
+#ifdef USE_TEMP_BUFFER
+   capture->buffers[MAX_V4L_BUFFERS].start = NULL;
+#endif
 
    /* w/o memset some parts  arent initialized - AKA: Fill it with zeros so it is clean */
    memset(capture,0,sizeof(CvCaptureCAM_V4L));
+
    /* Present the routines needed for V4L funtionality.  They are inserted as part of
       the standard set of cv calls promoting transparency.  "Vector Table" insertion. */
    capture->FirstCapture = 1;
@@ -1905,6 +1912,7 @@ public:
     virtual ~CvCaptureCAM_V4L_CPP() { close(); }
 
     virtual bool open( int index );
+    virtual bool open( const char* deviceName );
     virtual void close();
 
     virtual double getProperty(int) const;
@@ -1923,6 +1931,13 @@ bool CvCaptureCAM_V4L_CPP::open( int index )
     return captureV4L != 0;
 }
 
+bool CvCaptureCAM_V4L_CPP::open( const char* deviceName )
+{
+    close();
+    captureV4L = icvCaptureFromCAM_V4L(deviceName);
+    return captureV4L != 0;
+}
+
 void CvCaptureCAM_V4L_CPP::close()
 {
     if( captureV4L )
@@ -1963,4 +1978,15 @@ CvCapture* cvCreateCameraCapture_V4L( int index )
     return 0;
 }
 
+CvCapture* cvCreateCameraCapture_V4L( const char * deviceName )
+{
+    CvCaptureCAM_V4L_CPP* capture = new CvCaptureCAM_V4L_CPP;
+
+    if( capture->open( deviceName ))
+        return (CvCapture*)capture;
+
+    delete capture;
+    return 0;
+}
+
 #endif

modules/videoio/src/cap_v4l.cpp

@@ -270,12 +270,12 @@ struct CvCaptureCAM_V4L : public CvCapture
     int deviceHandle;
     int bufferIndex;
     int FirstCapture;
+    String deviceName;
 
     char *memoryMap;
     IplImage frame;
 
    __u32 palette;
-   int index;
    int width, height;
    __u32 fps;
    bool convert_rgb;
@@ -298,6 +298,7 @@ struct CvCaptureCAM_V4L : public CvCapture
    Range focus, brightness, contrast, saturation, hue, gain, exposure;
 
    bool open(int _index);
+   bool open(const char* deviceName);
 
    virtual double getProperty(int) const;
    virtual bool setProperty(int, double);
@@ -392,7 +393,7 @@ static bool try_palette_v4l2(CvCaptureCAM_V4L* capture)
   return capture->palette == capture->form.fmt.pix.pixelformat;
 }
 
-static int try_init_v4l2(CvCaptureCAM_V4L* capture, char *deviceName)
+static int try_init_v4l2(CvCaptureCAM_V4L* capture, const char *deviceName)
 {
   // Test device for V4L2 compability
   // Return value:
@@ -600,10 +601,7 @@ static void v4l2_create_frame(CvCaptureCAM_V4L *capture) {
 
 static int _capture_V4L2 (CvCaptureCAM_V4L *capture)
 {
-   char deviceName[MAX_DEVICE_DRIVER_NAME];
-   /* Print the CameraNumber at the end of the string with a width of one character */
-   sprintf(deviceName, "/dev/video%1d", capture->index);
-
+   const char* deviceName = capture->deviceName.c_str();
    if (try_init_v4l2(capture, deviceName) != 1) {
        /* init of the v4l2 device is not OK */
        return -1;
@@ -761,17 +759,16 @@ static int _capture_V4L2 (CvCaptureCAM_V4L *capture)
  * this also causes buffers to be reallocated if the frame size was changed.
  */
 static bool v4l2_reset( CvCaptureCAM_V4L* capture) {
-    int index = capture->index;
+    String deviceName = capture->deviceName;
     icvCloseCAM_V4L(capture);
-    capture->index = index;
+    capture->deviceName = deviceName;
     return _capture_V4L2(capture) == 1;
 }
 
 bool CvCaptureCAM_V4L::open(int _index)
 {
    int autoindex = 0;
-
-   index = -1; // set the capture to closed state
+   char _deviceName[MAX_DEVICE_DRIVER_NAME];
 
    if (!numCameras)
       icvInitCapture_V4L(); /* Havent called icvInitCapture yet - do it now! */
@@ -796,14 +793,21 @@ bool CvCaptureCAM_V4L::open(int _index)
      autoindex++;// i can recall icvOpenCAM_V4l with index=-1 for next camera
    }
 
-   index = _index;
-   FirstCapture = 1;
-   width = DEFAULT_V4L_WIDTH;
-   height = DEFAULT_V4L_HEIGHT;
-   fps = DEFAULT_V4L_FPS;
-   convert_rgb = true;
+   /* Print the CameraNumber at the end of the string with a width of one character */
+   sprintf(_deviceName, "/dev/video%1d", _index);
+   return open(_deviceName);
+}
 
-   return _capture_V4L2(this) == 1;
+bool CvCaptureCAM_V4L::open(const char* _deviceName)
+{
+    FirstCapture = 1;
+    width = DEFAULT_V4L_WIDTH;
+    height = DEFAULT_V4L_HEIGHT;
+    fps = DEFAULT_V4L_FPS;
+    convert_rgb = true;
+    deviceName = _deviceName;
+
+    return _capture_V4L2(this) == 1;
 }
 
 static int read_frame_v4l2(CvCaptureCAM_V4L* capture) {
@@ -1753,7 +1757,7 @@ static int icvSetPropertyCAM_V4L( CvCaptureCAM_V4L* capture,
 static void icvCloseCAM_V4L( CvCaptureCAM_V4L* capture ){
    /* Deallocate space - Hopefully, no leaks */
 
-   if (capture->index > -1)
+   if (!capture->deviceName.empty())
    {
        if (capture->deviceHandle != -1)
        {
@@ -1782,7 +1786,7 @@ static void icvCloseCAM_V4L( CvCaptureCAM_V4L* capture ){
      if (capture->frame.imageData)
          cvFree(&capture->frame.imageData);
 
-     capture->index = -1; // flag that the capture is closed
+     capture->deviceName.clear(); // flag that the capture is closed
    }
 };
 
@@ -1819,4 +1823,15 @@ CvCapture* cvCreateCameraCapture_V4L( int index )
     return NULL;
 }
 
+CvCapture* cvCreateCameraCapture_V4L( const char * deviceName )
+{
+    cv::CvCaptureCAM_V4L* capture = new cv::CvCaptureCAM_V4L();
+
+    if(capture->open( deviceName ))
+        return capture;
+
+    delete capture;
+    return NULL;
+}
+
 #endif

modules/videoio/src/precomp.hpp

@@ -102,6 +102,7 @@ struct CvVideoWriter
 };
 
 CvCapture * cvCreateCameraCapture_V4L( int index );
+CvCapture * cvCreateCameraCapture_V4L( const char* deviceName );
 CvCapture * cvCreateCameraCapture_DC1394( int index );
 CvCapture * cvCreateCameraCapture_DC1394_2( int index );
 CvCapture* cvCreateCameraCapture_MIL( int index );