Transformations

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ThePentiumGuy

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Matrix Translations in D3D

hey, im a little hazy about the subject of matrix transformations,
im trying to develop a (3d) racing game.
i have a mesh class which has an instance of a camera class, so my car and my platform mesh bothj have their own "cameras" (or you could say their own vector3's for Position, Target, and .. well the Up vector is the same for all of them - i have instances for each mesh so i can use them for world translatiion purposes)

ok,
my (skimmed down) render loop looks like this(in pseudocode as i dont really have a computer and im trying to figure this out)

BeginScene


Platform.SetupWorld
Platform.Render

Car.SetupWorld
Car.Render


EndScene
Present (i dont remmeber whether its present before Endscene or endsene before present lol but that doesnt matter ;))

my setup world sets up a LookAtLH view matrix and a perspectiveFOVLH projection matrix for each of htem

my dillema is this:

in order to get the effect that the car is moving (for example) forwards, i have to make the platform move backwards...
that's all said and done becuase whjen i push up i move the platform's camera down..etc

however, i want to be able to get the car's actual position and be able to do a mesh.intersect with it, for that ill need the car's "real" position,

i tried doing this

platform.setupworld 'becusae the platform moves
platform.render

car.render 'dotn move the car just rendfer it

and when i push(for example) space, the platform moves down, and the car moves up

but it gets confusing when i have to do Mesh.Intersect becuase the car is really 2x further into the platform then it thinks it is..

---

im sorta confusing myself here as i write this
my real plea is - can someone clarify matrix Transformations for me please
and tell me the best way to render my objects

pent
 
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My suggesting:
If your game is a first person game, you may simply alter the user camera view vectors and the object (car) vector at the same time, so you get the effect of moving, because any other objects (e.g. the world) is not moving.
That's how i did it for my program anyway.
 
hey dude i just thought of something,
and i think this is where my confusion is comign in

if i change the View camera with the car camera it should look like this when i push up
view.movecamera(3)
car.movecam(3)

that's all said and done

but also

if i render

identity
platform.setupworld
paltform.render

car.setupworld
car.render

d3ddev.transform.world = matrix.LookatLH(Camera.pos,camera.target, v3(0,1,0)

im pretty sure that last line's not gonna have any effect becuase it wont "change its position" like that in the last minute(you know what i mean?)
-
see the thing is, i got how to render the objects in a different position, but now - how would i change the view in which i see the objects?

in that case, would i have to change the Projectoin matrix? or the World matrix?

basically what i mean to say is -
after you've rendered all the objects, how wuold you change the "View" camera so that you see your scene from a different angle(in my case, behind the car)
 
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You've got things wrong. You can't change the view after you render things. The view must be correct during the rendering. After it's there it's there.

Also don't think in terms that each object has it's own camera. Objects only have position and orientation which is encoded in a matrix or vector (translation) + quaternion (rotation). You set this by setting the world matrix.

You only have one camera at a time. You could have more of them for different views, but you can only use one at a time. You set this matrix with LookAtLH for example and set it for the view matrix.

I hope this clears things up a bit.
 
I would have the platform fixed (always identity) and would only scroll the car. For the camera I'd calculate it's position to be somewhat behind and above the car and have the lookat vector at the position of the car.
 
so your saying

identity
platform.setupworld
paltform.render

identity
car.setupworld
'NOW check for collisions becuase the platform's "Back to where it was", and the platform's .. well its back to werhe it *should* be

Check For Collisions

identity 'the car never moves, the world moves
car.render

where the platform'll move down every time the car moves up..etc

edit: i corrected a lot of code
 
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I don't think I understand you. What does your setupworld do? how do you perform collision tests? You definitely want to set world matrix for the car. And I don't understand what you mean by moving the platform while moving the car. Why don't you have platform at fixed location.

I'd do things like this:

View = CameraViewMatrix
World = Identity
Platform.Render
World = CarMatrix
Car.Render

I skipped the collision as I don't know in what way you're doing it.
 
oh,sorry
my setupworld sets up a view (lookatLH) matrix for each individual mesh

my collision will be (in pseudocode: Mesh.Intersect(car's position,below the car) just to see whether the car is on(above) the platform))

how do u set a world matrix for the car?

thanks,
pent
 
Ok then you can't use your setupmatrix as you have it now.

To set up world matrix for the car you do something like this:
World = Matrix.Translation(CarPosition)

You could also do it like this if you'd like it to be rotated:
World = Matrix.Multiply(Matrix.RotationY(AngleInRadians), Matrix.Translation(CarPosition))

If you'll do collision detection like you said then you don't have to set world matrix. Just make sure that your car's position and below car are correct (meaning they are in world space coordinates).
 
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