Chase Camera Code

[technomage]

Hi Everyone

I have a little question (as always ).

I'm trying to implement a chase camera (a very basic one). I figured out the best way was to translate back a bit from the origin and render my model, that was the easy part.

The hard part is figuring out how to rotate the world in such a way that it looks right. I'm using ODE so I get the Position and Rotation of my "object" using
[pascal]
ShipPos := dBodyGetPosition(Ship.Body);
ShipRot := dBodyGetRotation(Ship.Body);
[/pascal]

Where ShipPos is a vector 3 and ShipRot is a 4x4 matrix.

My problem is I want to positon my camera using gluLookAt, so I need to calcuate the View and Up vectors from the information I get from ODE.

At this point my brain went to a walk. . Anyone have any suggestion on where to start?

Cheers

Dean

[Paulius]

View is the third row and up is second row, or if ODE matrices are mathematically correct, then that would be columns instead of rows.

[technomage]

I'll give that a go

Thanks

[technomage]

That worked a treat.

BTW the ODE matrix seems to be in columns not rows.

[WILL]

That worked a treat.

Ah... another proud PGD member... HELPED!

[JSoftware]

ODE using righthanded matrices?!? weird.. :?

[technomage]

OK, after a bit more testing it kinda worked, but not fully (rolling works OK, but pitching up or down just looked weird).

So my comment about the matirx being in columns might not be right, I'll do a bit more testing a let you all know.

[Paulius]

Since here camera is of the same orientation as the object this only works if camera is always directly behind the object (cameraPos = ObjectPos ?¢_" something * objectView)
Edit: maybe you?¢_Tre not giving gluLookAt what it wants: Center = CamraPos + ObjectView. Can't seem to come up with a proper way to compute Up with any camera position at the moment, I'll try to do this later

[technomage]

Hi guys

I thought I'd post some more code.

There is what I'm doing.

Firstly I render the world after setting the camera to the position of the object and using the values from the ShipRot matrix to set the view and up vectors

Then I render the actual object from behind.
[pascal]
glPushMatrix;
ShipPos := dBodyGetPosition(Ship.Body); // get position of ODE body
ShipRot := dBodyGetRotation(Ship.Body); // get rotation of ODE body
// set the camera
UserCam.PositionCamera(ShipPos[0], ShipPos[1], ShipPos[2],
ShipRot[8],ShipRot[9],ShipRot[10],
ShipRot[4],ShipRot[5],ShipRot[6]);
// call gluLookAt
UserCam.Look;
// render world
glPopMatrix;
glPushMatrix;
// set teh camerato be behind the object
UserCam.PositionCamera(0,10,-100,0,0,0,0,1,0);
// call gluLookAt
UserCam.Look;
// render player object
glPopMatrix;
[/pascal]

This works for rolling left and right, but not for pitching up or down.

[Paulius]

if PositionCamera uses data directlly for gluLookAt, then like I said it sould be
UserCam.PositionCamera(ShipPos[0], ShipPos[1], ShipPos[2],
ShipPos[0] + ShipRot[8], ShipPos[1] + ShipRot[9], ShipPos[2] +ShipRot[10],
ShipRot[4],ShipRot[5],ShipRot[6]);


And for any camera position
CamView = ObjectPos - CamPos;
CamRight = CrossProduct((0,1,0), CamView);
CamTop = CrossProduct(CamRight, CamView);