keywords: Houdini, Expression, VEX

Basic Notes

How to view VEX source code of VOP:

How to change point position:
Run Over: Points.

vector pos = @P;
if(pos.x < -3.5)
{
    @P = set(@P.x, @P.y + 5, @P.z);
}

How to remove points on polygon:
Run Over: Points.

if(@P.x < 250 && @P.z < 250 && @P.y > 250)
{
    removepoint(0, @ptnum);
}

How to remove primitive:
Run Over: Primitives.

if(@Frame > 5 && @P.z >10)
{
    removeprim(0, @primnum, 1);
}

How to add and set customized variables for points, vertices or primitives.

//add and set
i@my_var = 1;
//get
printf("%d\n", i@my_var);

How to set transform of primitives:
Run Over: Primitives or Points.

float scale = 1.5;
matrix transform = getpackedtransform(0, @primnum);
scale(transform, set(scale, scale, scale));
setpackedtransform(0, @primnum, transform);

Origin:
https://www.sidefx.com/forum/topic/72876/

How to rotate a point around another point alone a specifical axis:
1st way:

float angle = -90;
vector4 rot = quaternion(radians(angle), {1, 0, 0});
@P = qrotate(rot, @P + set(0, -500, -500));

2nd way:

matrix mat = maketransform(set(0, 1, 0), set(0, 0, -1), set(0, -tile_size, tile_size));
@P *= mat;

How to move a point alone normal:

@P += @N * chf('dist');

Points Computation

Snap an object to another precedurally
int pt = nearpoint ( 1, @P );
vector p = point ( 1, "P", pt );

@dist = distance2 ( @P, p );
i@nearpt = pt;

Sort by dist attribute.
Move wrangle code:

int pt = point ( 1, "nearpt", 0 );

vector p0 = point ( 1, "P", 0 );
vector p1 = point ( 2, "P", pt );

@P += p1 - p0;

Origin:
https://www.sidefx.com/forum/topic/82344/

Documents

HOUDINI help
https://www.sidefx.com/docs/houdini19.5/

Using VEX expressions
https://www.sidefx.com/docs/houdini/vex/snippets.html

Parameter expressions
https://www.sidefx.com/docs/houdini/network/expressions.html

Popular Built-in VEX Attributes (Global Variables)
https://stephanosterburg.gitbook.io/scrapbook/untitled/popular-built-in-vex-attributes-global-variables

Tutorials

The Nature of Vex.
https://www.mixtrn.com/nature-of-vex

Blogs

【Houdini】 表达式与VEX变量
https://www.yuelili.com/houdini-expression-and-vex-variable/

VEX Attribute Glossary
https://wiki.johnkunz.com/index.php?title=VEX_Attribute_Glossary

Houdini: Remove Outside Pieces Using Python
https://yudaitamamura.artstation.com/blog

Personal Notes (Tricks)

Killian Timsit
https://gist.github.com/killiantimsit

VEX for artists
https://github.com/kiryha/Houdini/wiki/vex-for-artists


“How can I be substantial if I do not cast a shadow? I must have a dark side also If I am to be whole.” ― C.G. Jung, Modern Man in Search of a Soul