svg - How do I compensate for the extra pixels added by stroke-linecap="round" in my calculated arc? -


i'm creating arc based on sunrise , sunset using following example of sunrise @ 6:15am

hour * 15 = 90 minutes  * 0.25 = 3.75 hour + minutes = 93.75

here function used calculate path.

polartocartesian: function (centerx, centery, radius, angleindegrees) {   var angleinradians = (angleindegrees - 90) * math.pi / 180.0    return {     x: centerx + (radius * math.cos(angleinradians)),     y: centery + (radius * math.sin(angleinradians))   } }, describearc: function (x, y, radius, startangle, endangle) {   var start = this.polartocartesian(x, y, radius, endangle)   var end = this.polartocartesian(x, y, radius, startangle)    var largearcflag = endangle - startangle <= 180 ? '0' : '1'    var d = [     'm', start.x, start.y,     'a', radius, radius, 0, largearcflag, 0, end.x, end.y   ].join(' ')   return d }

and here svg snippet

<path id="sun_ring_start" :d="getarcs(27, 93.75, 0)" fill="none" stroke="yellow" stroke-width="3" stroke-linecap="round" />

if use stroke-linecap="butt" stroke-width="3" can see arc starts @ 6:15 on clock face. when set stroke-linecap="round" stroke-width="3" arc starts earlier 6:15 because of pixels added stroke-linecap="round".

how can compensate pixels added stroke-linecap="round"?

work out round cap radius (half line width) corresponds in degrees. add or subract start/end angle appropriate.

var strokewidth = 3; var capsizeindegrees = (strokewidth/2) * 360 / cirumference.

it won't exact, should near enough needs.


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