Second Life Physics Scripting - Pinball #17 - Flipper Rotations Working

Rotations, what a nightmare. A nightmare of my own making, but I finally got the problem solved and it looks like I mostly had confused myself, but after lots of reading and a thousand tests I finally got the flipper to rotate on the test table.



Here is the final code for the timer routine that rotates the flipper in x number of steps.

    timer()
    {
        if (((rotation_tick>0) && (cur_rotation<max_rotation)) ||
            ((rotation_tick<0) && (cur_rotation>max_rotation)))
        
        {
        cur_rotation = cur_rotation + rotation_tick;

        // what is currently pointing up in the z direction
        // was originally in the -y direction.
        if (!orig_axis_flag)
        {
            orig_axis_flag = TRUE;
            orig_axis = llVecNorm(<0,-1,0> * llGetLocalRot());
        }
        
        // a rotation around the parents z normal
        //rotation z_45 = make_quaternion(parent_norm,rotation_tick*DEG_TO_RAD);
        rotation z_45 = llAxisAngle2Rot(orig_axis,rotation_tick*DEG_TO_RAD);
        
        // we need to find the axis which is the heal of the wedge
        // the original orientation of the flipper wedge is <0,0,1>
        // i use -1 to point at the heal of the wedge
        vector norm = <0,0,-1>;
        // rotate that norm so it points towards the point of the wedge
        norm = llVecNorm(norm * llGetLocalRot());
        // find the size of the wedge
        vector sz = llList2Vector(llGetPrimitiveParams([PRIM_SIZE]),0);
        // get the center location of the wedge
        vector flipper_pos = llGetLocalPos();
        // find the offset distance from the center
        vector offset = norm * (sz.z / 2);
        // add that offset to the flipper_pos to get the axis
        vector rot_axis = flipper_pos + offset;
        
        // calculate the new rotation by adding the z axis rotation
        // z_45 is the old name it is really z_plusang
        rotation new_rot =  llGetLocalRot()*z_45;  
        // http://wiki.secondlife.com/wiki/Rotation 
        // set the new local rotation
        llSetLocalRot(new_rot);
       
        // lsl wiki solution for non center rotation
        vector new_pos = rot_axis + ((flipper_pos - rot_axis) * z_45);
        llSetPos(new_pos);
        }
    else
        {
            // stop the timer and wait for the off event
            llSetTimerEvent(0);
        }
    } // timer

It turns out that the basic problem I was having was that I didn't think there was a llSetLocalRot because I already knew there wasn't a llSetLocalPos. So that final call to llSetLocalRot was llSetRot for the longest time and this added a little extra y rotation which caused the flipper to lean in the wrong direction. This was a ton of time to actually find this problem, but rotation can be like that and this is really just another bug in a long development process.

The crazy part is that I continued to work on this even though I knew the mechanic was not going to work. The flipper just takes too long to rotate each step and I don't want a flipper that only has two angles of bounce. Very annoying that there is a lot of work there and the api/engine doesn't support the mechanic I want to use, but then this is the way in software development. You have to make your designs fit the platforms you use and hope people make good platforms. SL is good, but there are a number of changes I would like to see made, but I don't think that is any different than any other api/platform.

I'd rather not see them do the kitchen sink stuff that was done with Java and basically ruined a very nice small system. Then again, they ignored the client side and just gave it up to flash which was a huge mistake that can't really be addressed at this point because now they made the foot print way too big to be a client side platform. I still love Java, I just think Schwartz badly mismanaged it just like he has mismanaged Sun. Sorry for the short rant.

So I think I'm going to use textures to do flippers flat near the back of the machine. We'll see how that turns out next.