screen capture using CGDisplayStreamCreateWithDispatchQueue

#include <sstream>
	#include <Cocoa/Cocoa.h>
	#include <CoreFoundation/CoreFoundation.h>
	#include <screencapture/mac/ScreenCaptureDisplayStream.h>
	namespace sc {
	ScreenCaptureDisplayStream::ScreenCaptureDisplayStream()
	:Base()
	,stream_ref(NULL)
	{
	dq = dispatch_queue_create("com.roxlu.screengrabber", DISPATCH_QUEUE_SERIAL);
	}
	int ScreenCaptureDisplayStream::init() {
	/* Fill our cached list of displays. */
	CGDirectDisplayID display_ids[10];
	uint32_t found_displays = 0;
	CGError err = CGGetActiveDisplayList(10, display_ids, &found_displays);
	if (kCGErrorSuccess != err) {
	printf("Error: failed to retrieve a list of active displays in `ScreenCaptureDisplayStream`.\n");
	return -1;
	}
	if (0 == found_displays) {
	printf("Error: we didn't find any active display.\n");
	return -2;
	}
	for (uint32_t i = 0; i < found_displays; ++i) {
	Display* display = new Display();
	ScreenCaptureDisplayStreamDisplayInfo* info = new ScreenCaptureDisplayStreamDisplayInfo();
	std::stringstream ss;
	ss << "Monitor " << i;
	info->id = display_ids[i];
	display->info = (void*)info;
	display->name = ss.str();
	displays.push_back(display);
	}
	return 0;
	}
	int ScreenCaptureDisplayStream::shutdown() {
	/* Release the stream. */
	if (NULL != stream_ref) {
	CFRelease(stream_ref);
	stream_ref = NULL;
	}
	/* Clear our cached list of displays. */
	for (size_t i = 0; i < displays.size(); ++i) {
	ScreenCaptureDisplayStreamDisplayInfo* info = static_cast<ScreenCaptureDisplayStreamDisplayInfo*>(displays[i]->info);
	if (NULL == info) {
	printf("Error: failed to cast back to `ScreenCaptureDisplayStreamDisplayInfo` in `ScreenCaptureDisplayStream`. Not supposed to happen. Leaking memory");
	}
	else {
	delete info;
	info = NULL;
	}
	delete displays[i];
	displays[i] = NULL;
	}
	displays.clear();
	return 0;
	}
	int ScreenCaptureDisplayStream::configure(Settings settings) {
	/* Get the implementation specific display id. */
	ScreenCaptureDisplayStreamDisplayInfo* info = static_cast<ScreenCaptureDisplayStreamDisplayInfo*>(displays[settings.display]->info);
	if (NULL == info) {
	printf("Error: failed to cast the display info of stream screen capture. Failed to setup\n");
	return -1;
	}
	/* Already a stream? Reset. */
	if (NULL != stream_ref) {
	if (0 == isStarted()) {
	if (0 != stop()) {
	printf("We're reconfiguring/setupping the display stream but we were captureing; stopping failed. Not supposed to happen; and you may leak memory here. We continue capturing though.\n");
	}
	}
	state &= ~SC_STATE_STARTED;
	state |= SC_STATE_STOPPED;
	CFRelease(stream_ref);
	stream_ref = NULL;
	}
	uint32_t pixel_format = 0;
	switch (settings.pixel_format) {
	case SC_420F: {
	pixel_format = '420f';
	break;
	}
	case SC_420V: {
	pixel_format = '420v';
	break;
	}
	case SC_BGRA: {
	pixel_format = 'BGRA';
	break;
	}
	case SC_L10R: {
	pixel_format = 'l10r';
	break;
	}
	default: {
	printf("Error: unsupported pixel format; cannot configure display stream.\n");
	return -2;
	}
	}
	__block PixelBuffer pixel_buffer;
	if (0 != pixel_buffer.init(settings.output_width, settings.output_height, settings.pixel_format)) {
	printf("Error: failed to setup the the pixel format.\n");
	return -3;
	}
	/* @todo > WE DON'T WANT TO MAKE THIS THE RESPONSIBILITY OF AN IMPLEMENTATION! */
	pixel_buffer.user = user;
	/* @todo make some settings available through API. */
	void* keys[2];
	void* values[2];
	CFDictionaryRef opts;
	keys[0] = (void *) kCGDisplayStreamShowCursor;
	values[0] = (void *) kCFBooleanTrue;
	opts = CFDictionaryCreate(kCFAllocatorDefault, (const void **) keys, (const void **) values, 1, NULL, NULL);
	/*
	UPDATE USING THIS CLEAN CODE: https://gist.github.com/roxlu/60f2f635347863d6384d
	TEST IF UPDATING THE CHANGED RECTS ONLY IS FASTER
	*/
	stream_ref = CGDisplayStreamCreateWithDispatchQueue(info->id,
	settings.output_width,
	settings.output_height,
	pixel_format,
	opts,
	dq,
	^(CGDisplayStreamFrameStatus status, /* kCGDisplayStreamFrameComplete, *FrameIdle, *FrameBlank, *Stopped */
	uint64_t time, /* Mach absolute time when the event occurred. */
	IOSurfaceRef frame, /* opaque pixel buffer, can be backed by GL, CL, etc.. This may be NULL in some cases. See the docs if you want to keep access to this. */
	CGDisplayStreamUpdateRef ref)
	{
	if (kCGDisplayStreamFrameStatusFrameComplete == status
	&& NULL != frame)
	{
	/*
	n.b. when the user needs to handle the pixel buffer after the call, it needs to make
	a copy. CGDisplayStream* supports a feature where you can increment the in-use-count, see
	the documention: https://developer.apple.com/library/mac/documentation/GraphicsImaging/Reference/Quartz_Services_Ref/index.html#//apple_ref/doc/c_ref/CGDisplayStreamFrameAvailableHandler
	*/
	IOSurfaceLock(frame, kIOSurfaceLockReadOnly, NULL);
	size_t plane_count = IOSurfaceGetPlaneCount(frame);
	if (2 == plane_count) {
	pixel_buffer.plane[0] = (uint8_t*)IOSurfaceGetBaseAddressOfPlane(frame, 0);
	pixel_buffer.stride[0] = IOSurfaceGetBytesPerRowOfPlane(frame, 0);
	pixel_buffer.plane[1] = (uint8_t*)IOSurfaceGetBaseAddressOfPlane(frame, 1);
	pixel_buffer.stride[1] = IOSurfaceGetBytesPerRowOfPlane(frame, 1);
	}
	else if (0 == plane_count) {
	pixel_buffer.plane[0] = (uint8_t*)IOSurfaceGetBaseAddress(frame);
	pixel_buffer.stride[0] = IOSurfaceGetBytesPerRow(frame);
	}
	else {
	printf("Error: unsupported plane count in the displaystream capture. Cannot setup the pixel buffer. Exiting now.\n");
	exit(EXIT_FAILURE);
	}
	callback(pixel_buffer);
	IOSurfaceUnlock(frame, kIOSurfaceLockReadOnly, NULL);
	}
	}
	);
	if (NULL == stream_ref) {
	printf("Error: failed to create a display stream that we use to capture the screen.\n");
	return -4;
	}
	return 0;
	}
	int ScreenCaptureDisplayStream::start() {
	CGError err = CGDisplayStreamStart(stream_ref);
	if (kCGErrorSuccess != err) {
	printf("Error: failed to start the display stream capturer. CGDisplayStreamStart failed: %d .\n", err);
	return -1;
	}
	return 0;
	}
	int ScreenCaptureDisplayStream::stop() {
	CGError err = CGDisplayStreamStop(stream_ref);
	if (kCGErrorSuccess != err) {
	printf("Error: failed to stop the display stream capturer. CGDisplayStreamStart failed: %d .\n", err);
	return -1;
	}
	return 0;
	}
	int ScreenCaptureDisplayStream::getDisplays(std::vector<Display*>& result) {
	result = displays;
	return 0;
	}
	int ScreenCaptureDisplayStream::getPixelFormats(std::vector<int>& formats) {
	formats.clear();
	formats.push_back(SC_420V);
	formats.push_back(SC_420F);
	formats.push_back(SC_BGRA);
	formats.push_back(SC_L10R);
	return 0;
	}
	}; /* namespace sc */

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