function pathArc(ctx, element, offset, spacing, end, circular) {
    const { x , y , startAngle: start , pixelMargin , innerRadius: innerR  } = element;
    const outerRadius = Math.max(element.outerRadius + spacing + offset - pixelMargin, 0);
    const innerRadius = innerR > 0 ? innerR + spacing + offset + pixelMargin : 0;
    let spacingOffset = 0;
    const alpha = end - start;
    if (spacing) {
        // When spacing is present, it is the same for all items
        // So we adjust the start and end angle of the arc such that
        // the distance is the same as it would be without the spacing
        const noSpacingInnerRadius = innerR > 0 ? innerR - spacing : 0;
        const noSpacingOuterRadius = outerRadius > 0 ? outerRadius - spacing : 0;
        const avNogSpacingRadius = (noSpacingInnerRadius + noSpacingOuterRadius) / 2;
        const adjustedAngle = avNogSpacingRadius !== 0 ? alpha * avNogSpacingRadius / (avNogSpacingRadius + spacing) : alpha;
        spacingOffset = (alpha - adjustedAngle) / 2;
    }
    const beta = Math.max(0.001, alpha * outerRadius - offset / PI) / outerRadius;
    const angleOffset = (alpha - beta) / 2;
    const startAngle = start + angleOffset + spacingOffset;
    const endAngle = end - angleOffset - spacingOffset;
    const { outerStart , outerEnd , innerStart , innerEnd  } = parseBorderRadius$1(element, innerRadius, outerRadius, endAngle - startAngle);
    const outerStartAdjustedRadius = outerRadius - outerStart;
    const outerEndAdjustedRadius = outerRadius - outerEnd;
    const outerStartAdjustedAngle = startAngle + outerStart / outerStartAdjustedRadius;
    const outerEndAdjustedAngle = endAngle - outerEnd / outerEndAdjustedRadius;
    const innerStartAdjustedRadius = innerRadius + innerStart;
    const innerEndAdjustedRadius = innerRadius + innerEnd;
    const innerStartAdjustedAngle = startAngle + innerStart / innerStartAdjustedRadius;
    const innerEndAdjustedAngle = endAngle - innerEnd / innerEndAdjustedRadius;
    ctx.beginPath();
    if (circular) {
        // The first arc segments from point 1 to point a to point 2
        const outerMidAdjustedAngle = (outerStartAdjustedAngle + outerEndAdjustedAngle) / 2;
        ctx.arc(x, y, outerRadius, outerStartAdjustedAngle, outerMidAdjustedAngle);
        ctx.arc(x, y, outerRadius, outerMidAdjustedAngle, outerEndAdjustedAngle);
        // The corner segment from point 2 to point 3
        if (outerEnd > 0) {
            const pCenter = rThetaToXY(outerEndAdjustedRadius, outerEndAdjustedAngle, x, y);
            ctx.arc(pCenter.x, pCenter.y, outerEnd, outerEndAdjustedAngle, endAngle + HALF_PI);
        }
        // The line from point 3 to point 4
        const p4 = rThetaToXY(innerEndAdjustedRadius, endAngle, x, y);
        ctx.lineTo(p4.x, p4.y);
        // The corner segment from point 4 to point 5
        if (innerEnd > 0) {
            const pCenter = rThetaToXY(innerEndAdjustedRadius, innerEndAdjustedAngle, x, y);
            ctx.arc(pCenter.x, pCenter.y, innerEnd, endAngle + HALF_PI, innerEndAdjustedAngle + Math.PI);
        }
        // The inner arc from point 5 to point b to point 6
        const innerMidAdjustedAngle = (endAngle - innerEnd / innerRadius + (startAngle + innerStart / innerRadius)) / 2;
        ctx.arc(x, y, innerRadius, endAngle - innerEnd / innerRadius, innerMidAdjustedAngle, true);
        ctx.arc(x, y, innerRadius, innerMidAdjustedAngle, startAngle + innerStart / innerRadius, true);
        // The corner segment from point 6 to point 7
        if (innerStart > 0) {
            const pCenter = rThetaToXY(innerStartAdjustedRadius, innerStartAdjustedAngle, x, y);
            ctx.arc(pCenter.x, pCenter.y, innerStart, innerStartAdjustedAngle + Math.PI, startAngle - HALF_PI);
        }
        // The line from point 7 to point 8
        const p8 = rThetaToXY(outerStartAdjustedRadius, startAngle, x, y);
        ctx.lineTo(p8.x, p8.y);
        // The corner segment from point 8 to point 1
        if (outerStart > 0) {
            const pCenter = rThetaToXY(outerStartAdjustedRadius, outerStartAdjustedAngle, x, y);
            ctx.arc(pCenter.x, pCenter.y, outerStart, startAngle - HALF_PI, outerStartAdjustedAngle);
        }
    } else {
        ctx.moveTo(x, y);
        const outerStartX = Math.cos(outerStartAdjustedAngle) * outerRadius + x;
        const outerStartY = Math.sin(outerStartAdjustedAngle) * outerRadius + y;
        ctx.lineTo(outerStartX, outerStartY);
        const outerEndX = Math.cos(outerEndAdjustedAngle) * outerRadius + x;
        const outerEndY = Math.sin(outerEndAdjustedAngle) * outerRadius + y;
        ctx.lineTo(outerEndX, outerEndY);
    }
    ctx.closePath();
}
Path the arc, respecting border radius by separating into left and right halves.

  Start      End

   1--->a--->2    Outer
  /           \
  8           3
  |           |
  |           |
  7           4
  \           /
   6<---b<---5    Inner