Hi, I'm a beginner of Houdini.
Can anyone teach me how to rotation a square or circle by using vex code?
Thank you very much!

Hi,

You can use this to rotate an object by 20 degrees in Y:

matrix3 m = ident ( );
rotate ( m, radians ( 20 ), { 0, 1, 0 } );
@P *= m;

you can as well use quaternions to do the same thing

@P = qrotate( quaternion( {0,20,0}, 0 ), @P );

if you are already familiar with matrices and quaternions it may be helpful to browse the docs to get see all the functions that VEX has to offet for manipulating them (or to read more about above mentioned ones)
http://www.sidefx.com/docs/houdini13.0/vex/functions/ [sidefx.com]

Also we have maketransform function for doing all transformation (Translate , Rotate , Scale) on the points.

maketransform(0,0,{ TX, TY, TZ },{ RX, RY, RZ},{ SX, SY, SZ },{ CEX, CEY, CEZ });

Example : ( Rotate points 45 degree along Y axis )


v@Temp = @P * maketransform(0,0,{ 0, 0, 0 },{ 0, 45, 0 },{ 1, 1, 1 },{ 0, 0, 0 });
@P = @Temp;

And there is something handy at times - optransform() to fetch transform matrix from any obj at scene level.

matrix M = optransform(“/obj/yourTransformedObj”) ;
@P *= M ;


Cheers !
- GM