User:Void Singer/Rotations

Common Rotation Tasks Simplified

These are a few simplifications of common rotation tasks for those (like me) who get a bit glassy eyed and overwhelmed reading the 'official' version...

• forward rotation vs reverse rotation
  • same as counter-clockwise vs clockwise (viewed from the positive end of the axis)
  • same as left turn vs right turn (viewed as if standing in the axis w/ head at positive end)

 //-- 2 ways to reverse rotation
 //-- use negative numbers in original variable, good for rotation that won't change
vector   vgVecLeftRotation = <.0, .0, 90.0>; //-- left 90 degrees around z-axis
vector   vgVecRightRotation = <.0, .0, -90.0>; //-- right 90 degrees around z-axis
 //-- use quaternion inversion, good for rotations that will reverse dynamically
vector   vgVecDegreesRotation = <.0, .0, 90>; //-- left 90 degrees around the z-axis
rotation vgRotConvertedDegrees = llEuler2Rot( vgVecDegreeRotation * DEG_TO_RAD ); //-- still left
vgRotConvertedDegrees.s *= -1; //-- reverses the rotation direction each time called

• rotating in global axis vs local
  • Global axis is the world, up, down, north, east, south, west
  • Local axis is the object, top, bottom, left-side, right-side, front-side, back-side.. imagine writing on a cardboard box

 //-- to rotate around the global axis (think stationary carousel)
llSetRot( llGetLocalRot() * vgRotConvertedDegrees );
 //-- to rotate around the local axis (think spinning tilted top) just reverse the order
llSetRot( vgRotConvertedDegrees  * llGetRot() );

• roatating a given point to match objects position/rotation
  • Do this to find where a point is in relation to an object (good for rezzors)
  • for instance if you want to know the point 1m from the top of an object, and 2m right..

vector vVecOffset = <2.0, .0, 1.0>;
 //-- even after rotating your object this will give the point in relation to it's new rotation
vector vVecCurrentOffset = llGetPos() + vVecOffset * llGetLocalRot();

• rotatating an objects POSITION around a given offset point
  • same idea as planets orbiting the sun

vector vVecOffset = <.0, .0, 1.0>; //-- the point we are rotating around in relation to our object
vector   vgVecArc = <.0, .0, 60.0>; //-- how far around the circle to travel each move
rotation vgRotArc = llEuler2Rot( vgVecArc * DEG_TO_RAD );
 //-- notice you have to move AND rotate, or else the new
 //-- position becomes a diagonal line instead of a circle
llSetPrimitiveParams( [PRIM_POSITION, llGetPos() + (vVecOffset - vVecOffset * vRotArc) * llGetLocalRot(),
                       PRIM_ROTATION, vRotArc * llGetLocalRot] );

• Warnings:
  • do NOT use rotation division to reverse direction
  • llSetPrimitiveParams & llSetRot do not work correctly for rotations in child prims

 //-- this might work in some cases, but fails in most, so don't use it!
llSetRot( llGetRot() / vgRotConvertedDegrees  );
 //-- this works in a child prim
llSetLocalRot( vgRotConvertedDegrees  * llGetLocalRot() );
 //-- these work incorrectly in child prims
llSetRot( vgRotConvertedDegrees  * llGetLocalRot() );
llSetPrimitiveParams( [PRIM_ROTATION, vgRotConvertedDegrees  * llGetLocalRot()] );
 //-- presumably this works incorrectly as well
llSetLinkPrimitiveParams( 2, [PRIM_ROTATION, vgRotConvertedDegrees  * llGetLocalRot()] );
 //-- see jira article SVC-93 for details + a workaround if you need to use llSetPrimitiveParams

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