VEX

VEX(Vector EXpressions)
- https://www.sidefx.com/docs/houdini/ref/expression_cookbook.html
jtomori/vex_tutorial
- https://github.com/jtomori/vex_tutorial
- https://jtomori.github.io/vex_tutorial/
에디터 설정
- Edit > Preference > Set External Text Editor
- VEXpression > 우클릭 > Expression > Edit in External Editor
- Visual Studio Code에 VEX 플러그인

// C:\Users\ (UserName) \Documents\houdini19.0\houdini.env
EDITOR = "C:\Users\(UserName)\AppData\Local\Programs\Microsoft VS Code\Code.exe"

절대로 point() 또는 prim() 표현식을 사용하지 마십시오(expressions). VEX 대응만 사용하십시오.
https://www.tokeru.com/cgwiki/?title=HoudiniVex
https://www.sidefx.com/learn/vex/
Attribute VOP
- Vex 시각화 그래프
Attribute Wrangle
- Vex 코딩
- Wrangle
  - This is a very powerful, low-level node that lets experts who are familiar with VEX tweak attributes using code.
  - https://english.stackexchange.com/questions/263712/what-does-come-on-lets-wrangle-up-the-cattle-mean
  - 소나 말들 관리

type@attribute

geometry sheet에서 확인 가능

i@myint         = 5;                                        // i | int

f@myfloat       = 12.234;                                   // f | float
u@myvector2     = {0.6, 0.5};                               // u | float2
v@myvector      = {1,2,3};                                  // v | float3
p@myquat        = {0,0,0,1};                                // p | float4

2@mymatrix2     = {1,2,3,4};                                // 2 | float2x2
3@mymatrix3     = {1,2,3,4,5,6,7,8,9};                      // 3 | float3x3
4@mymatrix4     = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16}; // 4 | float4x4

s@mystring      = 'a string';                               // s | string

d@mydict        = {};                                       // d | dict
d@mydict['key'] = 'value';

i[]@connected_pts = neighbours(0, @ptnum);                  // i[] | int[] array

https://sites.google.com/site/fujitarium/Houdini/sop/copy-sop

// https://www.sidefx.com/docs/houdini/vex/snippets.html
vector x0 = point(0, "P", @ptnum);
vector x1 = point(1, "P", @ptnum);


float dist = distance(x0, x1);
vector dir = normalize(x1 - x0);
vector next = x0 + dir * (dist / 2.0f);

@P = next;

@


@elemnum	현재 element	@id
@vtxnum	현재 vertex (linear)	흔히 말하는 버텍스
@ptnum	현재 point	포인트(중복된 포지션이 없다)
@primnum	현재 primitive	단일 엔티티(면 or 구 ...)
@numelem	총 element 갯수
@numvtx	총 vertex 갯수
@numpt	총 point 갯수
@numprim	총 primitive 갯수


@Time	Float time ($T)
@Frame	Float frame ($FF)
@SimTime	Float simulation time ($ST), only present in DOP contexts.
@SimFrame	Float simulation frame ($SF), only present in DOP contexts.
@TimeInc	Float time step (1/$FPS)


$VTX	vertexprimindex(0, @vtxnum);

geometry attribute

https://www.sidefx.com/docs/houdini/model/attributes.html


Geometry	id	int	A unique element ID
	name	string	이름
	P	vector	포지션
	N	vector	노말
	v	vector	속도 Velocity
	piece	int	조각
	pscale	float	Uniform scaling factor
	scale	vector	Whereas pscale is a single uniform scaling factor in all axes
Rendering	uv	vector	UV
Shader	Cd	vector	diffuse 색깔
	Cs	vector	specular 색깔
	Cr	vector	reflect 색깔
	Ce	vector	emission 색깔
	Ct	vector	transmit 색깔
	Alpha	float	Alpha transparency override. The viewport uses this to set the alpha of OpenGL geometry.
	rough	float	Roughness override.
	fresnel	float	Fresnel coefficient override.
	shadow	float	Shadow intensity override.
	sbias	float	Shadow bias override.
Particle	orient	vector4	Quaternion orientation of a particle
	up	vector	Represents the up vector of a particle’s local space
	rot	vector4	An additional offset-quaternion applied after all other attributes

Expression

$BBX = relbbox(@P).x
$BBY = relbbox(@P).y
$BBZ = relbbox(@P).z

Expression Local Variables
$PT	포인트 번호
$PR	프리미티브 번호
$CY	현재 사본 번호
$TX,$TY,$TZ	트랜스폼
$TX2,$TY2,$TZ2	두번째 입력에서 오는 포인트 위치
$NX,$NY,$NZ	노말
$CR,$CG,$CB,$CA	칼라
$VX,$VY,$VZ	벨로시티
$BBX,$BBY,$BBZ	바운딩 박스 내 점 위치（0 ~ 1）
$CEX,$CEY,$CEZ	기하학의 중심
$AGE	파티클 수명(초)
$LIFE	파티클 수명(0 ~ 1)
$XMIN,$XMAX,$YMIN,$YMAX,$ZMIN,$ZMAX	경계 범위
$SIZEX,$SIZEY,$SIZEZ	경계 크기

ch

https://www.sidefx.com/docs/houdini/vex/functions/ch.html


chramp(channel,ramppos, time)	조절 가능한 2차원 그래프 채널이 생긴다

Function


clamp(value, min, max)
fit(value, fromMin, fromMax, toMin, toMax)
point(geometry, attribute_name, pointnumber)	geometry는 입력 순서(0부터)
포지션 - minpos(geometry, point)	point에서 geometry에 레이를 쐈을시 가장 먼저 닿는 부분의 포지션
포인트 - nearpoint(geometry, pt)	geometry에 있는 모든 point 중에서 pt와 가장 가까운 point의 번호
Vector getbbox_size(geometry)	Computes the size of the bounding box for the geometry.

vector currP = @P;

// 현재 위치에서 1번 지오메트리와 맨 처음으로 마주치게될 포지션.
vector hittedP = minpos(1, currP);

// 현재 위치에서 1번 지오메트리에 있는 모든 포인트 중 가장 가까운 포인트번호.
int nearPointNumber = nearpoint(1, currP);

// 1번 지오메트리의 nearpointNumber의 _id값.
int id = point(1, "_id", nearPointNumber);

quaternion

vector4 orient = quaternion(maketransform(@N, @up));
vector euler  = quaterniontoeuler(orient,XFORM_XYZ);
v@rot = degrees(euler);

// maketransform: https://www.sidefx.com/docs/houdini/vex/functions/maketransform.html

vector4  quaternion(matrix3 rotations)
vector4  quaternion(float angle, vector axis)
vector4  quaternion(vector angleaxis)

vector  qrotate(vector4 quaternion, vector v)
vector  degrees(vector nums_in_rads)
vector  quaterniontoeuler(vector4 orient, int order)

vector4  slerp(vector4 q1, vector4 q2, float bias)

vector4  qmultiply(vector4 q1, vector4 q2)

Constant name	Rotation Order
XFORM_XYZ	Rotate order X, Y, Z
XFORM_XZY	Rotate order X, Z, Y
XFORM_YXZ	Rotate order Y, X, Z
XFORM_YZX	Rotate order Y, Z, X
XFORM_ZXY	Rotate order Z, X, Y
XFORM_ZYX	Rotate order Z, Y, X

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