Second Life Physics Scripting - Pinball #20 - Complete Puck Flipper System

Is this ever going to end? 20 posts already and there still seems like a ton of game code to add. This next step was all about trying to figure out where the ball crossed what I'm now calling the "puck flipper". I just typed it in once and it stuck, but now that I look at it I don't think it's the best name since it seems like the brain really wants to swap the f and p. Maybe it's just my brain? Oh well, it's in the code now.

Removing the flipper and hooking up the new puck flipper to the machine was a pretty simple exercise and only took a few minutes.


Anyway, it was pretty easy to setup the collision system, but actually a little hard to figure out where it crosses when you think about it in larger terms. Look at this first step.

   collision_start(integer total_number)
    {
        if (llDetectedName(0) == "ball")
        {
            // positions are in global coordinates

            // find the position of the collision...
            vector colpos = llDetectedPos(0);
            //llOwnerSay("colpos = "+(string)colpos);

            // find the location of the puck prim
            vector locpos = llGetPos();
            //llOwnerSay("locpos = "+(string)locpos);

            // subtract two to get local coordinates on the puck
            colpos = locpos - colpos;
        }
    }

This is pretty straight forward. Take the positions of the two elements and subtract their positions. This will give you the coordinates local to the puck. If you divide the y size by 4, this gives you the size of each puck positions. Multiply by the current puck and position and add a little bit in each direction and you can then compare that to the Y collision position.

Easy you say. Until you start to rotate the pinball machine around. I've built it aligned along the X axis, but if you rotate it 90 degrees into the Y axis then all the calculations will no longer work! You have to take this rotation into account. This next piece shows that code.

   collision_start(integer total_number)
    {
        if (llDetectedName(0) == "ball")
        {
            // find the position of the collision...
            vector colpos = llDetectedPos(0);
            //llOwnerSay("colpos = "+(string)colpos);

            // find the location of the puck prim
            vector locpos = llGetPos();
            //llOwnerSay("locpos = "+(string)locpos);

            // subtract two to get local coordinates on the puck
            colpos = locpos - colpos;
            llOwnerSay("colpos = "+(string)colpos);
            
            // divide by the global rotation so we are back
            // in the original build orientation
            rotation locrot = llGetRot();
            colpos = colpos / locrot;
            llOwnerSay("colpos after rot = "+(string)colpos);
        }
    }

Don't think I'm some sort of genuis and this just fell out of my brain. I spent at least an hour tweaking to get this right. For the longest time I had what I originally wrote colpos = colpos * locrot;. After I got my view port inside the pinball machine and dropped the ball at both edges a bunch of times I realized the Y values were giving opposite results when the table was rotated. I figured that using division of the rotation might swap the signs and sure enough it did and now I can move on.

I really like the puck mechanic so far and think it will be really effective. I think it will be even better if I used it with more than 4 positions. Given a bunch of positions it might even look just like a pong puck and allow for some really cool game mechanics. I've not seen anyone use this yet, so I'm excited to see this in action.

Second Life Physics Scripting - Pinball #15 - Flipper rotation and llSetPos problems

Spent a ton of time trying to get the flipper to rotate off axis.

At one point the llSetPos stopped working and I went back and created a test system to try and figure it out.



I kept calling llSetPos and nothing would move at all. This had to do with the requirement of calling llSetPos if you want to rotate off axis. Being my own worst enemy, I had done a test and changed some calls from llGetLocalPos to llGetPos. While there is no llSetLocalPos, the change from llGetLocalPos was what caused the problem. Since the flipper is a linked prim, the coordinates must be changed in local coordinates otherwise the world coordinates were off the map and nothing moved.

Then I also found the problem with the off axis rotation. Here is the final piece of code, with all of my debugs and junk code just so you can see how many interation tests went into it. This is from the link_message method outlined in the previous post.

// a rotation of 45 degrees around the z-axis
rotation z_45 = llEuler2Rot( <0, 0, -45 * DEG_TO_RAD> );
// the tilt of the table
rotation y_352 = llEuler2Rot( <0, 352 * DEG_TO_RAD, 0>);

// the original orientation of the flipper wedges 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());
//norm = llVecNorm(norm * llGetRot());

// find the size of the wedge
vector sz = llList2Vector(llGetPrimitiveParams([PRIM_SIZE]),0);
llOwnerSay("size = "+(string)sz);
vector flipper_pos = llGetLocalPos();
vector offset = norm * (sz.z / 2);
vector rot_axis = flipper_pos + offset;
//vector rot_axis = start_pos + offset;

llOwnerSay("flipper pos="+(string) flipper_pos);
llOwnerSay("rot_axis ="+(string) rot_axis);
llMessageLinked(dbg_marker, 1,(string)rot_axis, NULL_KEY);  
//llOwnerSay("distance from center to heal = "+(string)offset);
llOwnerSay("get rot = "+(string)llGetRot());
llOwnerSay("get local rot = "+(string)llGetLocalRot());
rotation new_rot = llGetLocalRot() * z_45;  // compute global rotation
//new_rot = new_rot * norm;
// http://wiki.secondlife.com/wiki/Rotation 
// find the rotated norm

vector rotated_offset = offset * new_rot;
llOwnerSay("new rot = "+(string)new_rot);
llSetRot(new_rot);

// ll wiki method
//vector rotatedOffset      = offset * z_45;    // rotate the offset to get the motion caused by the rotations
//vector newPos     = llGetPos() + (offset - rotatedOffset) * llGetRot();    // move the prim position by the rotated offset amount
//rotation newRot    = rot6X * llGetRot();

//llOwnerSay(" cur pos = "+(string)llGetLocalPos());
// lsl wiki solution
vector new_pos = rot_axis + ((flipper_pos - rot_axis) * z_45);
//vector new_pos = rot_axis + ((flipper_pos - rot_axis) * new_rot);
//vector new_pos = rot_axis + (offset * new_rot);
//vector new_pos = llGetLocalPos() - (offset * llGetLocalRot());
//vector newPos      = llGetLocalPos() + (offset - rotatedOffset) * llGetRot()
//new_pos.x = new_pos.x + 2;
llOwnerSay(" new pos = "+(string) new_pos);
llSetPos(new_pos);
//llOwnerSay(" after = "+(string)llGetLocalPos());

After all that, the problem ended up being this one line.

vector new_pos = rot_axis + ((flipper_pos - rot_axis) * z_45);
//vector new_pos = rot_axis + ((flipper_pos - rot_axis) * new_rot);

As you can see I was multiplying the offset by the new_rot which includes some of the initial rotations of the flipper. When all I really had to do is rotate it by the z_45 which is the change in rotation. This doesn't include the slight rotation of the table, but I'll be adding that as well soon. For now I'm going to do some more work on this test block first.

This still doesn't work all that well and I don't think it will behave like a pinball machine because the inbetween stages will not hit the ball properly. I'm going to make this a lot more complicated and fold it into a timer method and try rotating in increments. Wish me luck.