/*
?*?--Sparse?Optical?Flow?Demo?Program--
?*?Written?by?David?Stavens?（david.stavens@ai.stanford.edu）
?*/
#include?
#include?
#include?
#include?

static?const?double?pi?=?3.14159265358979323846;

inline?static?double?square（int?a）
{
	return?a?*?a;
}

/*?This?is?just?an?inline?that?allocates?images.??I?did?this?to?reduce?clutter?in?the
?*?actual?computer?vision?algorithmic?code.??Basically?it?allocates?the?requested?image
?*?unless?that?image?is?already?non-NULL.??It?always?leaves?a?non-NULL?image?as-is?even
?*?if?that?image‘s?size?depth?and/or?channels?are?different?than?the?request.
?*/
inline?static?void?allocateOnDemand（?IplImage?**img?CvSize?size?int?depth?int?channels?）
{
	if?（?*img?!=?NULL?）	return;

	*img?=?cvCreateImage（?size?depth?channels?）;
	if?（?*img?==?NULL?）
	{
		fprintf（stderr?“Error:?Couldn‘t?allocate?image.??Out?of?memory?\n“）;
		exit（-1）;
	}
}

int?main（void）
{
	/*?Create?an?object?that?decodes?the?input?video?stream.?*/
	CvCapture?*input_video?=?cvCaptureFromFile（
		“E:\\optical_flow_demo\\18_01.avi“
		）;
	if?（input_video?==?NULL）
	{
		/*?Either?the?video?didn‘t?exist?OR?it?uses?a?codec?OpenCV
		?*?doesn‘t?support.
		?*/
		fprintf（stderr?“Error:?Can‘t?open?video.\n“）;
		return?-1;
	}

	/*?Read?the?video‘s?frame?size?out?of?the?AVI.?*/
	CvSize?frame_size;
	frame_size.height?=
		（int）?cvGetCaptureProperty（?input_video?CV_CAP_PROP_frame_HEIGHT?）;
	frame_size.width?=
		（int）?cvGetCaptureProperty（?input_video?CV_CAP_PROP_frame_WIDTH?）;

	/*?Determine?the?number?of?frames?in?the?AVI.?*/
	long?number_of_frames;
	/*?Go?to?the?end?of?the?AVI?（ie:?the?fraction?is?“1“）?*/
	cvSetCaptureProperty（?input_video?CV_CAP_PROP_POS_AVI_RATIO?1.?）;
	/*?Now?that?we‘re?at?the?end?read?the?AVI?position?in?frames?*/
	number_of_frames?=?（int）?cvGetCaptureProperty（?input_video?CV_CAP_PROP_POS_frameS?）;
	/*?Return?to?the?beginning?*/
	cvSetCaptureProperty（?input_video?CV_CAP_PROP_POS_frameS?0.?）;

	/*?Create?a?windows?called?“Optical?Flow“?for?visualizing?the?output.
	?*?Have?the?window?automatically?change?its?size?to?match?the?output.
	?*/
	cvNamedWindow（“Optical?Flow“?CV_WINDOW_AUTOSIZE）;

	long?current_frame?=?0;
	while（true）
	{
		static?IplImage?*frame?=?NULL?*frame1?=?NULL?*frame1_1C?=?NULL?*frame2_1C?=?NULL?*eig_image?=?NULL?*temp_image?=?NULL?*pyramid1?=?NULL?*pyramid2?=?NULL;

		/*?Go?to?the?frame?we?want.??Important?if?multiple?frames?are?queried?in
		?*?the?loop?which?they?of?course?are?for?optical?flow.??Note?that?the?very
		?*?first?call?to?this?is?actually?not?needed.?（Because?the?correct?position
		?*?is?set?outsite?the?for（）?loop.）
		?*/
		cvSetCaptureProperty（?input_video?CV_CAP_PROP_POS_frameS?current_frame?）;

		/*?Get?the?next?frame?of?the?video.
		?*?IMPORTANT!??cvQueryframe（）?always?returns?a?pointer?to?the?_same_
		?*?memory?location.??So?successive?calls:
		?*?frame1?=?cvQueryframe（）;