camera is shaking, or maybe the world is?

[specialtactics]

Hi,

i am writing a game where the camera (instance of ICameraSceneNode*) is looking down on the game board. I attached the camera movement to the mouse but instead of the camera's view angle being constant (the camera's direction is!) it shakes and jitters. The effect is more noticable when the camera moves faster. I tried to pin down the problem, but it even occurs in the following code:

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	m_lookAt = vector3df(0.0, sin(0.008*g_gameTime)*10.0, 0.0);
	m_cam->setTarget(m_lookAt);
	m_cam->setPosition(m_lookAt + vector3df(0.0, 0.0, -25.0));
	m_cam->setUpVector(vector3df(0.0, 1.0, 0.0));

Also here it's more noticable when the camera is moving faster. The camera's view angle onto the board is not constant, it's changing pitch. The effect looks if the position of the camera is a bit ahead of the target. Which it isn't. It doesn't look like any of my variables are the cause, and i don't think it's a precision problem (of matrix calculations or whatever).

I changed the HelloWorld example (actually just changed 5 lines or so) to demonstrate the problem. the main.cpp can be found here: main.cpp and a windows exe here: HelloWorld.exe

Ok, i found a way to get rid of the effect, however i still don't know the source of the problem. In the changed helloworld demo i replaced

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	while(device->run())
	{
		float y = sin(device->getTimer()->getTime()*0.008)*10.0;
		cam->setPosition(vector3df(0.0, y, -40.0));
		cam->setTarget(vector3df(0.0, y, 0.0));

with

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	float y = 0.0;
	float prevY = 0.0;
	while(device->run())
	{
		prevY = y;
		y = sin(device->getTimer()->getTime()*0.008)*10.0;
		cam->setPosition(vector3df(0.0, y, -40.0));
		cam->setTarget(vector3df(0.0, prevY, 0.0));

So, i'm setting the camera's target not to the current target, but to the target of the previous frame (or i set the position ahead...). So it looks like it's a bug in the engine - something is updated/set at the wrong time and so the camera's view is messed up by 1 frame. I'll look closer at the irrlicht source now.

btw: to make the effect more visible (i suppose at 200fps or so it's hard to see) you can insert a Sleep(100)/usleep(100) in the main-loop. Which is what i did in the changed helloworld example.

[specialtactics]

OK, source found, too:

insert

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updateAbsolutePosition();

in CCameraSceneNode.cpp at line 218.

The problem is that the call (a few lines lower) View.buildCameraLookAtMatrixLH(pos, Target, up); used last frame's position. Because a call to CameraSceneNode->setPosition() updates the RelativePosition but doesn't update the AbsolutePosition immedietly.

[BlackNinjaGames]

I was thinking it was your use of sine.

Why is sine in there? Am I missing something?

[specialtactics]

That's just in my testing code to make the effect as visible as possible and not to use any of my game variables.. What the sine does is make the camera move along the y axis back and forth. The constant numbers set the speed and the amplitude of the bouncing.

[Guest]

This "updateabsoluteposition()" has been said a lot around here for jerky/non smooth camera updates - but I thought you were supposed to put it in your own code (in the update loop for example) and not need to put it in the source. Are you saying that it works better by putting it in the source - that there is a definate need for it there (and no performance loss?)

if so I willl put it in where you suggested in my next custom irrlicht as I do have jerky cameras at times even with high framerates (even locked frames)

[specialtactics]

Good point, Guest. You're right, that it should behave exactly the same, no matter if you put it in your code after you setPosition(), setTarget() and setUpVector() or if you put it in the engine where I suggested.

But since this is neither documented anywhere (or maybe I just didn't find the doc), nor intuitive, I think it should be done in the engine.

The cost is basically 1 matrix multiplaction which is done once per frame (just for the active camera), so it's probably not noticable.

[r3i]

Hi!
I've had the same problem and I've solved placing the camera a bit high than the ground.
The effect is that the collision manager makes the camera fall on the ground but after camera doesn't have any problems!

Try this trick...