qemu-usb: reduce cpu load by webcam model

if no new frame is available for capturing

Fixes #4078 #4196

repos/libports/src/lib/qemu-usb/dev-webcam.c

@@ -42,6 +42,7 @@ typedef struct USBWebcamState {
 	uint8_t    frame_toggle_bit;
 	bool       delay_packet;
 	bool       capture;
+	bool       timer_active;
 	uint8_t    watchdog;
 	uint8_t   *frame_pixel;
 } USBWebcamState;
@@ -202,8 +203,8 @@ static struct {
 	uint8_t  bpp;
 	uint16_t width;
 	uint16_t height;
-	uint32_t interval; /* dwFrameInterval */
-	void (*capture)(void *);
+	uint32_t interval; /* dwFrameInterval in 100ns units */
+	bool (*capture)(void *);
 } formats [2];
 
 static unsigned active_format()
@@ -400,7 +401,8 @@ static Property webcam_properties[] = {
 
 static void webcam_start_timer(USBWebcamState * const state)
 {
-	int64_t const now_ns = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+	state->timer_active = true;
+	uint64_t const now_ns = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 	timer_mod(state->timer, now_ns + 100ull * formats[active_format()].interval);
 }
 
@@ -420,6 +422,7 @@ static void usb_webcam_init_state(USBWebcamState *state)
 	state->delay_packet     = false;
 	state->capture          = false;
 	state->watchdog         = 0;
+	state->timer_active     = false;
 }
 
 static void usb_webcam_handle_reset(USBDevice *dev)
@@ -448,7 +451,6 @@ static void usb_webcam_setup_packet(USBWebcamState * const state, USBPacket * co
 {
 	unsigned packet_size           = vs_commit_state.dwMaxPayLoadTransferSize;
 	struct   payload_header header = { .length = 0, .bfh = 0 };
-	bool     start_timer           = !state->bytes_frame;
 
 	if (p->iov.size < packet_size)
 		packet_size = p->iov.size;
@@ -470,19 +472,16 @@ static void usb_webcam_setup_packet(USBWebcamState * const state, USBPacket * co
 	}
 
 	/* reset capture watchdog */
-	if (state->watchdog) {
+	if (state->watchdog)
 		state->watchdog = 0;
-		start_timer     = true;
-	}
 
 	/* check for capture state change */
 	if (!state->capture) {
 		state->capture = true;
-		start_timer    = true;
 		usb_webcam_capture_state_changed(state->capture);
 	}
 
-	if (start_timer)
+	if (!state->timer_active)
 		webcam_start_timer(state);
 
 	/* payload header */
@@ -533,6 +532,8 @@ static void webcam_timeout(void *opague)
 	USBDevice      *dev   = (USBDevice *)opague;
 	USBWebcamState *state = USB_WEBCAM(opague);
 
+	state->timer_active = false;
+
 	if (!state->capture)
 		return;
 
@@ -550,14 +551,18 @@ static void webcam_timeout(void *opague)
 		return;
 	}
 
+	/* start timer before requesting new frame to account the cpu time */
+	webcam_start_timer(state);
+
+	/* request next frame pixel buffer */
+	if (!formats[active_format()].capture(state->frame_pixel))
+		return;
+
 	USBPacket *p = state->delayed_packet;
 
 	state->delayed_packet = 0;
 	state->delay_packet   = false;
 
-	/* request next frame pixel buffer */
-	formats[active_format()].capture(state->frame_pixel);
-
 	/* continue usb transmission with new frame */
 	usb_webcam_setup_packet(state, p);
 	if (p->status == USB_RET_SUCCESS)

repos/libports/src/lib/qemu-usb/webcam-backend.h

@@ -18,8 +18,8 @@ struct webcam_config {
 };
 
 extern void webcam_backend_config(struct webcam_config *);
-extern void capture_bgr_frame(void * pixel);
-extern void capture_yuv_frame(void * pixel);
+extern bool capture_bgr_frame(void * pixel);
+extern bool capture_yuv_frame(void * pixel);
 extern void capture_state_changed(bool on, char const * format);
 
 #endif /* _WEBCAM_BACKEND_H_ */

repos/libports/src/lib/qemu-usb/webcam.cc

@@ -34,6 +34,7 @@ struct Capture_webcam
 	Gui::Area            const  _area;
 	bool                 const  _vflip;
 	uint8_t              const  _fps;
+	bool                        _force_update { false };
 	Attached_dataspace          _ds { _env.rm(), _capture.dataspace() };
 	Constructible<Reporter>     _reporter { };
 
@@ -54,9 +55,18 @@ struct Capture_webcam
 		return area;
 	}
 
-	void update_yuv(void *frame)
+
+	bool update_yuv(void *frame)
 	{
-		_capture.capture_at(Capture::Point(0, 0));
+		if (!_area.valid())
+			return false;
+
+		bool changed = _force_update;
+		_capture.capture_at(Capture::Point(0, 0)).for_each_rect([&](auto) {
+			changed = true; });
+
+		if (!changed)
+			return false;
 
 		int const src_stride_argb = _area.w() * 4;
 		int const dst_stride_yuy2 = _area.w() * 2;
@@ -64,30 +74,55 @@ struct Capture_webcam
 		libyuv::ARGBToYUY2(_ds.local_addr<uint8_t>(), src_stride_argb,
 		                   reinterpret_cast<uint8_t*>(frame), dst_stride_yuy2,
 		                   _area.w(), _area.h());
+
+		if (_force_update)
+			_force_update = false;
+
+		return true;
 	}
 
-	void update_bgr(void *frame)
+	bool update_bgr(void *frame)
 	{
-		_capture.capture_at(Capture::Point(0, 0));
+		if (!_area.valid())
+			return false;
 
-		uint8_t * const bgr  = reinterpret_cast<uint8_t *>(frame);
-		Pixel_rgb888 *  data = reinterpret_cast<Pixel_rgb888 *>(_ds.local_addr<void>());
+		bool changed = false;
 
-		for (int y = 0; y < _area.h(); y++) {
-			unsigned const row = _vflip ? y : _area.h() - 1 - y;
-			unsigned const row_byte = (row * _area.w() * 3);
-			for (int x = 0; x < _area.w(); x++) {
-				bgr[row_byte + x * 3 + 0] = data->b();
-				bgr[row_byte + x * 3 + 1] = data->g();
-				bgr[row_byte + x * 3 + 2] = data->r();
+		uint8_t            * const bgr  = reinterpret_cast<uint8_t *>(frame);
+		Pixel_rgb888 const * const data = _ds.local_addr<Pixel_rgb888>();
 
-				data++;
+		auto const &update_fn = ([&](auto &rect) {
+			changed = true;
+			for (int y = rect.y1(); y <= rect.y2(); y++) {
+				unsigned const row      = _vflip ? y : _area.h() - 1 - y;
+				unsigned const row_byte = (row * _area.w() * 3);
+
+				for (int x = rect.x1(); x < rect.x2(); x++) {
+					auto &pixel = data[y * _area.w() + x];
+					bgr[row_byte + x * 3 + 0] = pixel.b();
+					bgr[row_byte + x * 3 + 1] = pixel.g();
+					bgr[row_byte + x * 3 + 2] = pixel.r();
+				}
 			}
-		}
+		});
+
+		if (_force_update) {
+			/* update whole frame */
+			_force_update = false;
+			Rect const whole(Point(0,0), _area);
+			_capture.capture_at(Capture::Point(0, 0));
+			update_fn(whole);
+		} else
+			_capture.capture_at(Capture::Point(0, 0)).for_each_rect(update_fn);
+
+		return changed;
 	}
 
 	void capture_state_changed(bool on, char const * format)
 	{
+		/* next time update whole frame due to format changes or on/off */
+		_force_update = true;
+
 		if (!_reporter.constructed())
 			return;
 
@@ -123,14 +158,14 @@ extern "C" void capture_state_changed(bool on, char const * format)
 	capture->capture_state_changed(on, format);
 }
 
-extern "C" void capture_bgr_frame(void * pixel)
+extern "C" bool capture_bgr_frame(void * pixel)
 {
-	capture->update_bgr(pixel);
+	return capture->update_bgr(pixel);
 }
 
-extern "C" void capture_yuv_frame(void * pixel)
+extern "C" bool capture_yuv_frame(void * pixel)
 {
-	capture->update_yuv(pixel);
+	return capture->update_yuv(pixel);
 }