Is getRayFromScreenCoordinates() dependent on last frame?

[piiichan]

I'll try to explain the situation as best as I can, so it may be a bit wordy!

I have a moving player character in a diablo-like game.
The view is isometric, the camera is orthogonal. As soon as the character moves, the camera position and target are updated , so the camera is always looking at the character and is always at the same position relatively to the character. (the camera is NOT a child node of the character node, I do it via camera->setPosition()).
When the left mouse button is down, I use ISceneCollisionManager::getCollisionPoint() and ISceneCollisionManager::getRayFromScreenCoordinates() to find where the player wants to move.

Everything is working correctly when the character is still.

However, when the character is moving, the collision point I get is not correct: I get the collision point of the previous frame.
In other words, I get the collision point just as if the camera was still at the previous location. This is obvious when the character moves fast: the collision point is very far from the mouse location and the offset from the current mouse location is exactly the distance traveled at each frame.
I thought at first I was calling the functions in a wrong order, but everything in my code is correct: I first move the camera, THEN get the collision point from screen coordinates.
After some experiments, calling ISceneManager::drawAll() alone, after repositionning the camera, and before doing the collision test, makes the collision test work fine.

How can I solve this collision problem without calling ISceneManager::drawAll() before doing the collision test?

[rogerborg]

Call camera->updateAbsolutePosition() after moving it.

[piiichan]

Call camera->updateAbsolutePosition() after moving it.

I tried it, but it still won't work.

Here is where I set the camera position and target:

Code: Select all

camera->setPosition( vector3df(
		node->getPosition().X + offset,
		hypoLength,
		node->getPosition().Z - offset));
camera->setTarget( node->getPosition() );
g_smgr->drawAll();
...

As you see, I have to call drawAll(), even if this code is not between driver-beginScene() and driver->endScene(). Calling camera->updateAbsolutePosition() instead does not solve the problem.

I wonder why is the drawAll() method of the scene manager correcting the problem?

[CuteAlien]

I think it has to do with the stuff called in OnRegisterSceneNode. I am having a similar problem, but couldn't solve it so far. I think the solution is probably to use an own camera. But not sure, maybe someone has a better solution, I also need to check this some more.

[rogerborg]

Sorry, I misread your problem. It looks like you want to call node->updateAbsolutePosition() before calling node->getPosition().

[dlangdev]

also...

check out the function ...

void CSceneManager::drawAll()

in CSceneManager.cpp

you'll get more information on how positions are calculated.

it could be in the block where it renders default objects, tho.

[Dark_Kilauea]

if you are using any animators, they will execute on smgr->drawall().

[piiichan]

I think it has to do with the stuff called in OnRegisterSceneNode

check out the function void CSceneManager::drawAll()

Thanks a lot to CuteAlien and dlangdev respectively, the problem is solved. Instead of calling drawAll() from the scene manager, I now call OnRegisterSceneNode() from the camera, like this

Code: Select all

ICameraSceneNode* camera = g_smgr->getActiveCamera();
camera->setPosition( vector3df(
		node->getPosition().X + offset,
		hypoLength,
		node->getPosition().Z - offset));
camera->setTarget( node->getPosition() );

//g_smgr->drawAll();			// called to avoid strange behavior of collision detection, but not needed anymore
camera->OnRegisterSceneNode();	// cleaner solution

It looks like you want to call node->updateAbsolutePosition() before calling node->getPosition().

rogerborg, I tried this also, but it still won't work...

if you are using any animators, they will execute on smgr->drawall().

Dark_Kilauea, thanks for reminding me this fact. I've read this in the API doc, so I checked if my animators and particle systems were affected by this isolated call to smgr->drawall(), but everything was fine. I think it's because animators rely on time to animate, not on frame rate, so it's pretty safe on this side.

Although ISceneNode::OnRegisterSceneNode solves my problem, I don't understand why... the API doc says

This method is called just before the rendering process of the whole scene.

Nodes may register themselves in the render pipeline during this call, precalculate the geometry which should be renderered, and prevent their children from being able to register themselves if they are clipped by simply not calling their OnRegisterSceneNode method. If you are implementing your own scene node, you should overwrite this method with an implementation code looking like this:

... this is quite blur to me...

[BlindSide]

"OnRegisterSceneNode" used to be called "OnPreRender", so it's actually hijacked for alot more stuff than just registering the scene node on the render list.

[piiichan]

So is it safe to call it the way I do?
What about efficiency? Is it a CPU intensive method?

[dlangdev]

you may have to call CSceneManager::drawAll() tho.

there's a ton of stuff CSceneManager::drawAll() has to cover. you can't simply drop it like that.

oh my god...

what have i done!

[Dark_Kilauea]

Dark_Kilauea, thanks for reminding me this fact. I've read this in the API doc, so I checked if my animators and particle systems were affected by this isolated call to smgr->drawall(), but everything was fine. I think it's because animators rely on time to animate, not on frame rate, so it's pretty safe on this side.

I was reminding you of this fact because animators do change position every frame (due to interpolation) so they could easily be throwing your ray tracing off.

Most animators seem to run during OnRegisterSceneNode()