I have written some code to preform 3D picking that for some reason dosn't work entirely correct! (Im using LWJGL just so you know.)

I posted this at stackoverflow at first but after researching some more in to my problem i found this neat site and tought that you guys might be more qualified to answer this question.

This is how the code looks like:

if(Mouse.getEventButton() == 1) {
  if (!Mouse.getEventButtonState()) {
    Camera.get().generateViewMatrix();

    float screenSpaceX = ((Mouse.getX()/800f/2f)-1.0f)*Camera.get().getAspectRatio();
    float screenSpaceY = 1.0f-(2*((600-Mouse.getY())/600f));
    float displacementRate = (float)Math.tan(Camera.get().getFovy()/2);

    screenSpaceX *= displacementRate;
    screenSpaceY *= displacementRate;

    Vector4f cameraSpaceNear = new Vector4f((float) (screenSpaceX * Camera.get().getNear()), (float) (screenSpaceY * Camera.get().getNear()), (float) (-Camera.get().getNear()), 1);
    Vector4f cameraSpaceFar = new Vector4f((float) (screenSpaceX * Camera.get().getFar()), (float) (screenSpaceY * Camera.get().getFar()), (float) (-Camera.get().getFar()), 1);

    Matrix4f tmpView = new Matrix4f();
    Camera.get().getViewMatrix().transpose(tmpView);
    Matrix4f invertedViewMatrix = (Matrix4f)tmpView.invert();

    Vector4f worldSpaceNear = new Vector4f();
    Matrix4f.transform(invertedViewMatrix, cameraSpaceNear, worldSpaceNear);

    Vector4f worldSpaceFar = new Vector4f();
    Matrix4f.transform(invertedViewMatrix, cameraSpaceFar, worldSpaceFar);


    Vector3f rayPosition = new Vector3f(worldSpaceNear.x, worldSpaceNear.y, worldSpaceNear.z);
    Vector3f rayDirection = new Vector3f(worldSpaceFar.x - worldSpaceNear.x, worldSpaceFar.y - worldSpaceNear.y, worldSpaceFar.z - worldSpaceNear.z);

    rayDirection.normalise();

    Ray clickRay = new Ray(rayPosition, rayDirection);

    Vector tMin = new Vector(), tMax = new Vector(), tempPoint;
    float largestEnteringValue, smallestExitingValue, temp, closestEnteringValue = Camera.get().getFar()+0.1f;
    Drawable closestDrawableHit = null;
    for(Drawable d : this.worldModel.getDrawableThings()) {
        // Calcualte AABB for each object... needs to be moved later...
        firstVertex = true;
        for(Surface surface : d.getSurfaces()) {
            for(Vertex v : surface.getVertices()) {
                worldPosition.x = (v.x+d.getPosition().x)*d.getScale().x;
                worldPosition.y = (v.y+d.getPosition().y)*d.getScale().y;
                worldPosition.z = (v.z+d.getPosition().z)*d.getScale().z;
                worldPosition = worldPosition.rotate(d.getRotation());
                if (firstVertex) {
                    maxX = worldPosition.x; maxY = worldPosition.y; maxZ = worldPosition.z;
                    minX = worldPosition.x; minY = worldPosition.y; minZ = worldPosition.z;
                    firstVertex = false;
                } else {
                    if (worldPosition.x > maxX) {
                        maxX = worldPosition.x;
                    }
                    if (worldPosition.x < minX) {
                        minX = worldPosition.x;
                    }
                    if (worldPosition.y > maxY) {
                        maxY = worldPosition.y;
                    }
                    if (worldPosition.y < minY) {
                        minY = worldPosition.y;
                    }
                    if (worldPosition.z > maxZ) {
                        maxZ = worldPosition.z;
                    }
                    if (worldPosition.z < minZ) {
                        minZ = worldPosition.z;
                    }
                }
            }
        }

        // ray/slabs intersection test...


        // clickRay.getOrigin().x + clickRay.getDirection().x * f = minX
        // clickRay.getOrigin().x - minX = -clickRay.getDirection().x * f
        // clickRay.getOrigin().x/-clickRay.getDirection().x - minX/-clickRay.getDirection().x = f
        // -clickRay.getOrigin().x/clickRay.getDirection().x + minX/clickRay.getDirection().x = f


        largestEnteringValue = -clickRay.getOrigin().x/clickRay.getDirection().x + minX/clickRay.getDirection().x;
        temp = -clickRay.getOrigin().y/clickRay.getDirection().y + minY/clickRay.getDirection().y;
        if(largestEnteringValue < temp) {
            largestEnteringValue = temp;
        }
        temp = -clickRay.getOrigin().z/clickRay.getDirection().z + minZ/clickRay.getDirection().z;
        if(largestEnteringValue < temp) {
            largestEnteringValue = temp;
        }

        smallestExitingValue = -clickRay.getOrigin().x/clickRay.getDirection().x + maxX/clickRay.getDirection().x;
        temp = -clickRay.getOrigin().y/clickRay.getDirection().y + maxY/clickRay.getDirection().y;
        if(smallestExitingValue > temp) {
            smallestExitingValue = temp;
        }
        temp = -clickRay.getOrigin().z/clickRay.getDirection().z + maxZ/clickRay.getDirection().z;
        if(smallestExitingValue < temp) {
            smallestExitingValue = temp;
        }


            if(largestEnteringValue > smallestExitingValue) {
                //System.out.println("Miss!");
            } else {
                if (largestEnteringValue < closestEnteringValue) {
                    closestEnteringValue = largestEnteringValue;
                    closestDrawableHit = d;
                }
            }

    }
    if(closestDrawableHit != null) {
        System.out.println("Hit at: (" + clickRay.setDistance(closestEnteringValue).x + ", " + clickRay.getCurrentPosition().y + ", " + clickRay.getCurrentPosition().z);
        this.worldModel.removeDrawableThing(closestDrawableHit);    
    }
  }
}

I just don't understand what's wrong, the ray are shooting and i do hit stuff that gets removed but the result of the ray are verry strange it sometimes removes the thing im clicking at, sometimes it removes things thats not even close to what im clicking at, and sometimes it removes nothing at all.

Edit:

Okay so i have continued searching for errors and by debugging the ray (by painting smal dots where it travles) i can now se that there is something oviously wrong with the ray that im sending out... it has its origin near the world center (nearer or further away depending on where on the screen im clicking) and always shots to the same position no matter where I direct my camera...

My initial toughts is that there might be some error in the way i calculate my viewMatrix (since it's not possible to get the viewmatrix from the gluLookAt method in lwjgl; I have to build it my self and I guess thats where the problem is at)...

Edit2:

This is how i calculate it currently:

private double[][] viewMatrixDouble = {{0,0,0,0}, {0,0,0,0}, {0,0,0,0}, {0,0,0,1}};

public Vector getCameraDirectionVector() {
    Vector actualEye = this.getActualEyePosition();
    return new Vector(lookAt.x-actualEye.x, lookAt.y-actualEye.y, lookAt.z-actualEye.z);
}

public Vector getActualEyePosition() {
    return eye.rotate(this.getRotation());
}

public void generateViewMatrix() {

    Vector cameraDirectionVector = getCameraDirectionVector().normalize();
    Vector side = Vector.cross(cameraDirectionVector, this.upVector).normalize();
    Vector up = Vector.cross(side, cameraDirectionVector);

    viewMatrixDouble[0][0] = side.x;                    viewMatrixDouble[0][1] = up.x;                  viewMatrixDouble[0][2] = -cameraDirectionVector.x;                 
    viewMatrixDouble[1][0] = side.y;                    viewMatrixDouble[1][1] = up.y;                  viewMatrixDouble[1][2] = -cameraDirectionVector.y;                 
    viewMatrixDouble[2][0] = side.z;                    viewMatrixDouble[2][1] = up.z;                  viewMatrixDouble[2][2] = -cameraDirectionVector.z;                 


    /*
    Vector actualEyePosition = this.getActualEyePosition();
    Vector zaxis = new Vector(this.lookAt.x - actualEyePosition.x, this.lookAt.y - actualEyePosition.y, this.lookAt.z - actualEyePosition.z).normalize();
    Vector xaxis = Vector.cross(upVector, zaxis).normalize();
    Vector yaxis = Vector.cross(zaxis, xaxis);
    viewMatrixDouble[0][0] = xaxis.x;                   viewMatrixDouble[0][1] = yaxis.x;                   viewMatrixDouble[0][2] = zaxis.x;                  
    viewMatrixDouble[1][0] = xaxis.y;                   viewMatrixDouble[1][1] = yaxis.y;                   viewMatrixDouble[1][2] = zaxis.y;                  
    viewMatrixDouble[2][0] = xaxis.z;                   viewMatrixDouble[2][1] = yaxis.z;                   viewMatrixDouble[2][2] = zaxis.z;                  
    viewMatrixDouble[3][0] = -Vector.dot(xaxis, actualEyePosition); viewMatrixDouble[3][1] =-Vector.dot(yaxis, actualEyePosition);  viewMatrixDouble[3][2] = -Vector.dot(zaxis, actualEyePosition);
    */
    viewMatrix = new Matrix4f();
    viewMatrix.load(getViewMatrixAsFloatBuffer());
}

Would be verry greatfull if anyone could verify if this is wrong or right, and if it's wrong; supply me with the right way of doing it... I have read alot of threads and documentations about this but i can't seam to wrapp my head around it...

Edit3:

Okay with the help of Byte56 (thanks alot for the help) i have now concluded that it's not the viewMatrix that is the problem... I still get the same messedup result; anyone that think that they can find the error in my code, i certenly can't, have bean working on this for 3 days now :(