Hi,

I'm trying to create my own 3D engine, but I have some problems with implementing scene graph. I want to achieve this:

Assume that our character is on the ship. He doesn't move relative to the ship, but he moves relative to world(where ship go, he go too). Not only he, but everything what is on the board.

I'm using actor component system and I'm storing WorldMatrix inside transform component(But I have idea to store scene node directly to the actor, as a component, is this a bad idea?)

I have created scene graph based on GCC one(but it doesn't work in deeper hierarchy what is what I want to achieve).

My second question is:

I read : http://www.gamedev.net/topic/619283-are-scene-graphs-worth-it/

that I should separate rendering from scene graph(I'm reading GCC and they used scene graph as rendering system).

But if I do it, is then scene graph unnecessary?

Thank you for your advices!

This is exactly like I'm doing it:

|- Car -|- Player

|

Root(just identity matrix) -| - Ship -|- AI

-|- Machine gun

|

|- Another AI(walking on the land)

But I had some problems with concatenating matrices, like car stopped, but Player was still moving, or(the funniest one) player in the car was moving with exponential speed.

I solved this by using three matrices(is there a better way? This one brings a lot of matrix concatenations):

1) Parent transformation

2) Local transformation relative to the parent

3) World transformation

Now, I'm using scene graph for computing world transformations and visibility tests and I'm trying to experiment with graphics too.

Ok, I try to rely less on what others are saying, but I want to find and develop things in the best way I can do it.

And what about rendering system? What is meaning to separate it?(This or not(If I understand it correctly)?: Traverse scene graph, compute world matrices, find which scene nodes can be renderered and add them into rendering queue?)

And my final question(or request), can someone review my English, please? Thank you

I solved this by using three matrices(is there a better way? This one brings a lot of matrix concatenations):

1) Parent transformation

2) Local transformation relative to the parent

3) World transformation

That's the general idea behind a hierarchy tree of transformations.

In fact what you really need are just ToParent relative (local) transformation matrices. Then you can get all global (world) transformations just by multiplying the ToParent matrix of the actual node with the ToParent matrix of its parent with the ToParent matrix of this parent's parent.... all the way to the top-most node. The top-most node has no parents and you assume it's global transform to be identity.

This is very inefficient, because you'll be repeating the same multiplications a lot, unless each parent has only one descendant. So it's a good idea to store the global (world) transform of each node and when you go from the top to the bottom, you calculate the world matrix of each node by just multiplying its ToParent matrix with the parent's World matrix (which already incorporates all the ToParent*ToParent*ToParent... multiplications).

Yes, I'm using system like a stack for computing world matrices.

No, I don't have a specific post (just if you look at it, if it is readable or you must read a lot to understand what I mean)

Probably my last question is: Where is a good place to attach scene node to the Actor?