arrowSDF: Three-Dimensional Directional Arrow Distance Field

Geometric Vector Representation in Signed Distance Space

The arrowSDF function computes the signed distance from any 3D point to an arrow-shaped geometry. This primitive combines cylindrical shaft geometry with conical tip mathematics, enabling directional visualization and vector field representation.

Mathematical Foundation

The arrow SDF operates through coordinate transformation and geometric decomposition:

$$d_{\text{arrow}} = \min\{d_{\text{shaft}}, d_{\text{tip}}\} \cdot \text{sign}(s)$$

where the transformation matrix aligns the local coordinate system with the arrow direction vector:

$$\mathbf{M} = \begin{pmatrix} t_z^2k + t_y & t_x & -t_xt_zk \\ -t_x & t_y & -t_z \\ -t_xt_zk & t_z & t_x^2k + t_y \end{pmatrix}$$

with $k = \frac{1}{1 + t_y}$ and $\mathbf{t} = \frac{\text{start} - \text{end}}{|\text{start} - \text{end}|}$.

Function Signature

Parameter	Type	Description
v	vec3	Sample point position
start	vec3	Arrow tail position
end	vec3	Arrow head position
baseRadius	float	Shaft cylinder radius
tipRadius	float	Arrowhead base radius
tipHeight	float	Arrowhead cone height

Implementation Demonstrations

ライブエディター

const fragment = () => {
      const pos = vec3(uv.x.mul(4).sub(2), uv.y.mul(4).sub(2), 0)
      const start = vec3(-1.5, 0, 0)
      const end = vec3(1.5, 0, 0)
      const dist = arrowSDF(pos, start, end, 0.25, 0.6, 0.8)
      const arrowShape = float(0.05).smoothstep(0, dist)
      const arrowFill = float(0).step(dist.negate())
      const color = arrowFill.mul(vec3(1, 0.3, 0.1)).add(arrowShape.mul(vec3(1, 0.8, 0.2)))
      return vec4(color, 1)
}