C + OpenCV: IplImage with circular buffer - c

Question

I'm trying to implement a circular buffer for use as a frame buffer with OpenCV (using C).
I've shamelessly stolen the circular buffer implementation from this post to save reinventing the wheel:
EDIT: OK, so I've redefined a few things. Namely I implemented my own circular buffer. Now I'm getting errors which don't make sense.
Here is the circular buffer implementation I'm using:
#define BUFFER_SIZE 100
typedef struct
{
IplImage* queue[BUFFER_SIZE];
IplImage *in;
IplImage *out;
int num_frames;
int in_ctr;
int out_ctr;
int update_flag;
} frame_buffer;
Here is the get function:
IplImage* buff_get()
{
IplImage* nextfr;
if(frbuff.num_frames == 0)
{
return NULL;
}
nextfr = frbuff.out++;
if(++frbuff.out_ctr == BUFFER_SIZE)
{
frbuff.out = &frbuff.queue[0];
frbuff.out_ctr = 0;
}
--frbuff.num_frames;
return nextfr;
}
Here is the put function:
int buff_put(IplImage* nextfr)
{
if(++frbuff.num_frames > BUFFER_SIZE)
{
return 0;
}
frbuff.in++;
frbuff.in = nextfr;
if(++frbuff.in_ctr == BUFFER_SIZE)
{
frbuff.in = &frbuff.queue[0];
frbuff.in_ctr = 0;
}
return 1;
}
Everything seems to go OK. Frames appear on the buffer, which I know because I can print the size out. But it all goes bad when I try to show the image that's on the buffer.
If I then try to do this:
IplImage* curr_frame = cvCreateImage(cvSize(640,480),8,3);
cvNamedWindow("proc_window",CV_WINDOW_AUTOSIZE);
cvShowImage("proc_window",curr_frame);
while(1)
{
if(buff_size() > 0)
{
if(buff_flag_check()) curr_frame = buff_get();
if(curr_frame != NULL)
{
cvShowImage("proc_window",curr_frame);
}
}
I recieve the following error upon calling cvShowImage():
OpenCV Error: Bad flag (parameter or structure field) (Unrecognized or unsupported array type) in cvGetMat, file /home/fagg/src/OpenCV-2.3.1/modules/core/src/array.cpp, line 2482
terminate called after throwing an instance of 'cv::Exception'
what(): /home/fagg/src/OpenCV-2.3.1/modules/core/src/array.cpp:2482: error: (-206) Unrecognized or unsupported array type in function cvGetMat
I'm quite confused as to what's going on here. Hopefully someone with fresher eyes than myself can see what's going on...

Answer 1

The snippet of code you provided won't compile as cb_init() takes a pointer to a circular_buffer as first argument.
and if you get a segfault in cb_init() it is because malloc() fails to return the requested size and the implementation in the link does not handle errors.
void cb_init(circular_buffer *cb, size_t capacity, size_t sz)
{
cb->buffer = malloc(capacity * sz);
if(cb->buffer == NULL)
// handle error
cb->buffer_end = (char *)cb->buffer + capacity * sz;//segfault when using cb->buffer which is null in case of malloc() failure
cb->capacity = capacity;
cb->count = 0;
cb->sz = sz;
cb->head = cb->buffer;
cb->tail = cb->buffer;
}