SDF - Dashed Circle (HLSL), source: https://www.shadertoy.com/view/7tyGWw

sdDashedCircle.hlsl

float arcRadius = length(p);

// Compute the radial distance field coming out from the center of a torus
const float hw = (RadiusOuter-RadiusInner)*0.5; // half width from center of torus to edge
float radialDF = arcRadius - (RadiusOuter-hw);  // creates a torus
radialDF = abs(radialDF)-hw;                    // give an inside and outside to the torus

// Compute the gradient along the length of the arc
float arcGradient = atan2(p.y,p.x)/6.283185; 
arcGradient = frac(arcGradient*NumDashes); 
arcGradient = abs((arcGradient-0.5)*2.0);          // make the gradient a linear, continuous 0-1-0-1 repeating pattern
arcGradient = arcGradient-DashRatio;               // split the arc into positive and negative sections
float theta = arcGradient * (3.1415927/NumDashes); // gets us a signed angle from the nearest dash edge, in radians

// figure out the point closest to us on the nearest dash edge
float s,c;
sincos(theta,s,c);
float edgeProjection = clamp(c*arcRadius,RadiusInner,RadiusOuter); // project point p but bound it between the innner and outer radii of the dash
float2 nearestEdgeP = mul(float2x2(c,-s,s,c),p) * edgeProjection/arcRadius;  
float edgeDF = length(p-nearestEdgeP);

return (theta   >0.0) ? edgeDF   : 
       (radialDF>0.0) ? radialDF :
                        max(-edgeDF,radialDF);