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modeling with distance functions



After having posted about the basics of distance functions in several places (pouet, my blog, shadertoy, private emails, etc), i thought it might make sense to put these together in centralized place. Here you will find the distance functions for basic primitives, plus the formulas for combining them together for building more complex shapes, as well as some distortion functions that you can use to shape your objects. Hopefully this will be usefull for those rendering scenes with raymarching. You can see some of the results you can get by using these techniques in the raymarching distance fields article. Lastly, this article doesn't include lighting tricks, nor marching acceleartion tricks or more advanced techniques as recursive primitives or fractals.


primitives

All primitives are centered at the origin. You will have to transform the point to get arbitrarily rotated, translated and scaled objects (see below).


Sphere - signed

float sdSphere( vec3 p, float s )
{
  return length(p)-s;
}

Box - unsigned

float udBox( vec3 p, vec3 b )
{
  return length(max(abs(p)-b,0.0));
}

Round Box - unsigned

float udRoundBox( vec3 p, vec3 b, float r )
{
  return length(max(abs(p)-b,0.0))-r;
}

Box - signed

float sdBox( vec3 p, vec3 b )
{
  vec3  di = abs(p) - b;
  float mc = maxcomp(di);
  return min(mc,length(max(di,0.0)));
}

Torus - signed

float sdTorus( vec3 p, vec2 t )
{
  vec2 q = vec2(length(p.xz)-t.x,p.y);
  return length(q)-t.y;
}

Cylinder - signed

float sdCylinder( vec3 p, vec3 c )
{
  return length(p.xz-c.xy)-c.z;
}

Cone - signed

float sdCone( vec3 p, vec2 c )
{
    // c must be normalized
    float q = length(p.xy);
    return dot(c,vec2(q,p.z));
}

Plane - signed

float sdPlane( vec3 p, vec4 n )
{
  // n must be normalized
  return dot(p,n.xyz) + n.w;
}

Hexagonal Prism - unsigned

float udHexPrism( vec3 p, vec2 h )
{
    float q = abs(p);
    return max(q.z-h.y,max(q.x+q.y*0.57735,q.y)-h.x);
}


Most of these functions can be modified to use other norms than the euclidean. By replacing length(p), which computes (x^2+y^2+z^2)^(1/2) by (x^n+y^n+z^n)^(1/n) one can get variations of the basic primitives that have rounded edges rather than sharp ones.


Torus82 - signed

float sdTorus82( vec3 p, vec2 t )
{
  vec2 q = vec2(length2(p.xz)-t.x,p.y);
  return length8(q)-t.y;
}

Torus88 - signed

float sdTorus88( vec3 p, vec2 t )
{
  vec2 q = vec2(length8(p.xz)-t.x,p.y);
  return length8(q)-t.y;
}



distance operations

The d1 and d2 parameters in the following functions are the distance to the two distance fields to combine together.


Union

float opU( float d1, float d2 )
{
    return min(d1,d2);
}

Substraction

float opS( float d1, float d2 )
{
    return max(-d1,d2);
}

Intersection

float opI( float d1, float d2 )
{
    return max(d1,d2);
}



domain operations

Where "primitive", in the examples below, is any distance formula really (one of the basic primitives aboce, a combination, or a complex distance field).


Repetition

float opRep( vec3 p, vec3 c )
{
    vec3 q = mod(p,c)-0.5*c;
    return primitve( q );
}

Rotation/Translation

vec3 opTx( vec3 p, mat4 m )
{
    vec3 q = invert(m)*p;
    return primitive(q);
}

Scale

float opScale( vec3 p, float s )
{
    return primitive(p/s)*s;
}



distance deformations

You must be carefull when using distance transformation functions, as the field created might not be a real distance function anymore. You will probably need to decrease your step size, if you are using a raymarcher to sample this. The displacement example below is using sin(20*p.x)*sin(20*p.y)*sin(20*p.z) as displacement pattern, but you can of course use anything you might imagine.


Displacement

float opDisplace( vec3 p )
{
    float d1 = primitive(p);
    float d2 = displacement(p);
    return d1+d2;
}

Blend

float opBlend( vec3 p )
{
    float d1 = primitiveA(p);
    float d2 = primitiveB(p);
    floar dd = smoothcurve(d1-d2);
    return mix(d1,d2,dd);
}



domain deformations

Domain deformation functions do not preserve distances neither. You must decrease your marching step to properly sample these functions (proportionally to the maximun derivative of the domain distortion function). Of course, any distortion function can be used, from twists, bends, to random noise driven deformations.


Twist

float opTwist( vec3 p )
{
    float c = cos(20.0*p.y);
    float s = sin(20.0*p.y);
    mat2  m = mat2(c,-s,s,c);
    vec3  q = vec3(m*p.xz,p.y);
    return primitive(q);
}

Cheap Bend

float opCheapBend( vec3 p )
{
    float c = cos(20.0*p.y);
    float s = sin(20.0*p.y);
    mat2  m = mat2(c,-s,s,c);
    vec3  q = vec3(m*p.xy,p.z);
    return primitive(q);
}




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iņigo quilez 2008