Return the right type and error when opening VideoCapture fails

When opening a video capture OpenCV signals an error when open() fails,
however we are ignoring this error and not setting it when returning
from Go bindings functions.

Furthermore open() function returns bool. We are returning the open()
error as integeer, which is ok in C/C++ world as it's implicitly cast
into particular bool value - we want to make this explicit in GoCV so we
are returning bool now as per OpenCV.

videoio.cpp

@@ -9,11 +9,11 @@ void VideoCapture_Close(VideoCapture v) {
     delete v;
 }
 
-int VideoCapture_Open(VideoCapture v, const char* uri) {
+bool VideoCapture_Open(VideoCapture v, const char* uri) {
     return v->open(uri);
 }
 
-int VideoCapture_OpenDevice(VideoCapture v, int device) {
+bool VideoCapture_OpenDevice(VideoCapture v, int device) {
     return v->open(device);
 }
 

videoio.go

@@ -169,15 +169,22 @@ func VideoCaptureFile(uri string) (vc *VideoCapture, err error) {
 	cURI := C.CString(uri)
 	defer C.free(unsafe.Pointer(cURI))
 
-	C.VideoCapture_Open(vc.p, cURI)
+	if !C.VideoCapture_Open(vc.p, cURI) {
+		err = fmt.Errorf("Error opening file: %s", uri)
+	}
+
 	return
 }
 
 // VideoCaptureDevice opens a VideoCapture from a device and prepares
 // to start capturing.
 func VideoCaptureDevice(device int) (vc *VideoCapture, err error) {
 	vc = &VideoCapture{p: C.VideoCapture_New()}
-	C.VideoCapture_OpenDevice(vc.p, C.int(device))
+
+	if !C.VideoCapture_OpenDevice(vc.p, C.int(device)) {
+		err = fmt.Errorf("Error opening device: %d", device)
+	}
+
 	return
 }
 

videoio.h

@@ -19,8 +19,8 @@ typedef void* VideoWriter;
 // VideoCapture
 VideoCapture VideoCapture_New();
 void VideoCapture_Close(VideoCapture v);
-int VideoCapture_Open(VideoCapture v, const char* uri);
-int VideoCapture_OpenDevice(VideoCapture v, int device);
+bool VideoCapture_Open(VideoCapture v, const char* uri);
+bool VideoCapture_OpenDevice(VideoCapture v, int device);
 void VideoCapture_Set(VideoCapture v, int prop, double param);
 double VideoCapture_Get(VideoCapture v, int prop);
 int VideoCapture_IsOpened(VideoCapture v);

videoio_test.go

@@ -37,9 +37,13 @@ func TestVideoCaptureInvalid(t *testing.T) {
 }
 
 func TestVideoCaptureFile(t *testing.T) {
-	vc, _ := VideoCaptureFile("images/small.mp4")
+	vc, err := VideoCaptureFile("images/small.mp4")
 	defer vc.Close()
 
+	if err != nil {
+		t.Errorf("%s", err)
+	}
+
 	if !vc.IsOpened() {
 		t.Error("Unable to open VideoCaptureFile")
 	}
@@ -62,6 +66,13 @@ func TestVideoCaptureFile(t *testing.T) {
 	if img.Empty() {
 		t.Error("Unable to read VideoCaptureFile")
 	}
+
+	vc2, err := VideoCaptureFile("nonexistent.mp4")
+	defer vc2.Close()
+
+	if err == nil {
+		t.Errorf("Expected error when opening invalid file")
+	}
 }
 
 func TestVideoWriterFile(t *testing.T) {