FPS counter is incorrect when opening a rendering heavy data and keep increasing

[mwestphal]

Describe the bug
The FPS counter (Z key) is completely incorrect when opening a dataset that is rendering limited;

To Reproduce
Steps to reproduce the behavior:

1. Open the file using f3d bicycle/point_cloud/iteration_7000/point_cloud.ply
2. Press Z
3. Zoom in and out
4. FPS show around 300 FPS and keep increasing, while I hardly have 3 fps.

simplescreenrecorder-2025-07-09_22.37.20.mp4

Expected behavior
Correct FPS

System Information:

• OS: Any
• GPU and GPU driver: GTX 1660

F3D Information
Paste the content of f3d --version or f3d-console.exe --version on Windows:
3.2.0 binary

Additional context
Add any other context about the problem here.

[snoyer]

Probably a different bug but still "incorrect FPS under heavy load": if you really push it you can get past 0 fps and achieve -2147483648 fps:

f3d-raytracting-fps.mp4

vtkF3DUIActor::UpdateFpsValue has FrameTimes.pop_front(); in a while loop and / this->FrameTimes.size(); afterwards

f3d/vtkext/private/module/vtkF3DUIActor.cxx

Lines 93 to 101 in 3bec77e

	while (this->TotalFrameTimes > 1.0)
	{
	double oldestFrameTime = this->FrameTimes.front();
	this->FrameTimes.pop_front();
	this->TotalFrameTimes -= oldestFrameTime;
	}
	double averageFrameTime = this->TotalFrameTimes / this->FrameTimes.size();

but the loop doesn't check FrameTimes.size() so it could empty it and then it would divide by zero (and then static_cast<int>(std::nan("")) is -2147483648)