Clear calibration data on a calibration restart

Restarting the calibration now clears the existing calibration data.
This should (finally) solve #70 (I hope).

In addition, a safety check has been built into the calibration routine,
which should prevent further pointstart and pointend requests when the
EyeTribe suddenly decides that it has been calibrated (which can happen,
for yet unknown reasons).

pygaze/_eyetracker/libeyetribe.py

@@ -193,17 +193,32 @@ def calibrate(self):
 		calibrated = False
 		calibresult = None
 		while not quited and not calibrated:
+
+			# Clear the existing calibration.
+			if self.eyetribe._tracker.get_iscalibrated():
+				self.eyetribe._lock.acquire(True)
+				self.eyetribe.calibration.clear()
+				self.eyetribe._lock.release()
 
 			# Wait for a bit.
 			clock.pause(1500)
 
 			# start a new calibration
-			self.eyetribe._lock.acquire(True)
-			self.eyetribe.calibration.start(pointcount=len(calibpoints))
-			self.eyetribe._lock.release()
+			if not self.eyetribe._tracker.get_iscalibrating():
+				self.eyetribe._lock.acquire(True)
+				self.eyetribe.calibration.start(pointcount=len(calibpoints))
+				self.eyetribe._lock.release()
 
 			# loop through calibration points
 			for cpos in calibpoints:
+				# Check whether the calibration is already done.
+				# (Not sure how or why, but for some reason some data
+				# can persist between calbrations, and the tracker will
+				# simply stop allowing further pointstart requests.)
+				if self.eyetribe._tracker.get_iscalibrated():
+					break
+
+				# Draw a calibration target.
 				self.draw_calibration_target(cpos[0], cpos[1])
 				# wait for a bit to allow participant to start looking at
 				# the calibration point (#TODO: space press?)

pygaze/_eyetracker/pytribe.py

@@ -1505,7 +1505,7 @@ def start(self, pointcount=9, max_attempts=5):
 				{'pointcount':pointcount})
 		    # return value or error
 		    if response['statuscode'] == 200:
-		        return
+		        return True
 		    self.abort()
 		raise Exception("Error in calibration.start: %s (code %d)" \
 			% (response['values']['statusmessage'],response['statuscode']))