Display FPS for VTK on Python

In the last post, I discussed how to get started with VTK on Python. In this post, I will show how to add support to show frames per second (FPS). The idea to calculate FPS is straight forward: keep track of the number of frames (N) that were rendered in last T seconds. Then fps defined a N/T fps.

To calculate FPS we will add an observer to the EndEvent command of the vtkRenderer. In the callback function, we will count the number of frames rendered in the last T seconds and calculate FPS. Here is the complete code of the FpsObserver:

import vtk
from timeit import default_timer as timer

class FpsObserver:
	def __init__(self, renderer, x=0, y=0):
		self.mRenderer = renderer
		self.mRenderer.AddObserver(vtk.vtkCommand.EndEvent, self)
		self.ActorPosX = x
		self.ActorPosY = y
		self.mFrameCount    = 0         # Number of frames collected since last FPS was calculated.
		self.mStartTime     = timer()   # The last time FPS was calculated.
		self.mFpsUpdateRate = 1         # How often to update FPS in seconds.
	def setPosition(self, x, y):
		self.ActorPosX = x
		self.ActorPosY = y
		self.mFpsActor.SetPosition(self.ActorPosX, self.ActorPosY)
	def __call__(self, caller, event):
		if event == "EndEvent":
			self.mFrameCount = self.mFrameCount + 1
			if timer() - self.mStartTime > self.mFpsUpdateRate:
				_currentTime     = timer()
				_duration        = _currentTime - self.mStartTime
				_fps = self.mFrameCount/_duration
				self.mFpsActor.SetInput("FPS: {:.2f}".format(_fps))
				self.mStartTime  = _currentTime
				self.mFrameCount = 0
	def _createFpsTextActor(self):
		self.mFpsActor = vtk.vtkTextActor()
		self.mFpsActor.GetTextProperty().SetColor([1, 1, 1])
		self.mFpsActor.SetPosition(self.ActorPosX, self.ActorPosY)

To use FpsObserver, we just need to initialize it as self.mFpsObserver = FpsObserver.FpsObserver(self.mRenderer). That’s it, this will display the FPS for last one seconds!

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