Screen Flickering problem...

[simpson.jon]

I was wondering if anyone might know of a reason the screen would flicker when using globalRevolve? While rotating it appears to blink and if you let go of the controls at the right moment the objects all dissappear. I've tried commenting out lines to see if I can get it to stop and I found that it would if I commented out the lines

Code:

myPosition = Vector3.Transform( myRevolveTarget - myPosition, Matrix.CreateFromQuaternion(rotate)) + myRevolveTarget;

My computer doesn't support the pixel shaders used in the HMEngine so I've rewritten parts to use the basic effect, is that the problem? I don't understand what that line could possibly do to make the screen flicker, but it does work without flickering without that line. Although the camera rotation is off.

Thanks for any help!

[simpson.jon]

I've realized what I think is the problem but I don't know how to fix it. My camera appears to be rotating 180 degrees every frame so the screen 'flickers' but it's really looking the wrong way. My myRevolveTarget points to an object in front of the camera, and the myPosition is the current position so I'm lost. It always seems to be weird little problems that back me up.

Looking at the console using writeline I noticed that the vectors switch signs in the (myRevolveTarget - myPosition). My outputs looks like this when trying to do a revolve of any type.

Revolve target{X:0 Y:0 Z:0}, My postion {X:1.979998 Y:0 Z:4000},
Revolve target{X:0 Y:0 Z:0}, My postion {X:-1.991998 Y:0 Z:-4000},
Revolve target{X:0 Y:0 Z:0}, My postion {X:2.003998 Y:0 Z:4000}

Is that suppose to be a dot product or something to find the up vector between the two? Any help would be much appreciated.

[simpson.jon]

I've been messing with the code and have come to understand what I believe every part to mean, but it still performs incorrectly with my program. My problem is the flickering like before but I can't seem to understand what about my program causes the value of myPosition to oscilate.

Code:

public void Revolve(Vector3 target, Vector3 axis, float angle) {
Rotate(axis, angle);
axis = Vector3.Transform(axis, Matrix.CreateFromQuaternion(myRotation));
Quaternion rotate = Quaternion.CreateFromAxisAngle(axis, angle);
myPosition = Vector3.Transform(target - myPosition, Matrix.CreateFromQuaternion(rotate));

Update();
}

For this function in my code the target is passed, say Vector3.zero, the X axis is passed (1,0,0), and .03f is passed as my rotation angle. When it comes down to the myPosition = Vector3.... line myPosition switches signs on all the values that are not Zero. So if my myPosition =(0, 50, 4000) and it subtracts itself from zero it gets (0, -50, -4000).

Only it does recieve some modification from the quaternion and the values change. I'm guessing something about the vector3.transform function should stop the values of myPosition from changing in this manner but I can't figure out what. Any advice would be most helpful. Thanks.

[mikeschuld]

that code is wrong. it is from before a fix that was mentioned elsewhere. Try this instead:

      public void Revolve(Vector3 axis, float angle) {
         Vector3 revolveAxis = Vector3.Transform(axis, Matrix.CreateFromQuaternion(myRotation));
         Quaternion rotate = Quaternion.CreateFromAxisAngle(revolveAxis, angle);

         myPosition = Vector3.Transform(
            myPosition - target, Matrix.CreateFromQuaternion(rotate)
         ) + target;

         Rotate(axis, angle);
      }


Update: I swapped the target - position to position - target.. This is what was causing the flickering.

[simpson.jon]

I tried using the new code and I still get the flicker. How does the transform function prevent the numbers from flipping?

The exact function I'm using to call the Revolve is

Code:

CameraManager.ActiveCamera.Revolve(new Vector3(1, 0, 0), -0.05f);

At the time I call revolve the target location is 0,0,0. It functions exactly like I would expect and revolves around the target but every other frame is drawn from the opposite side looking at the same angle so you can't see the object. Could it be something outside of the camera class that makes the function not work?