draw2d/curve/arc.go
2015-04-23 15:36:56 +02:00

38 lines
757 B
Go

// Copyright 2010 The draw2d Authors. All rights reserved.
// created: 21/11/2010 by Laurent Le Goff
package curve
import (
"math"
)
// TraceArc trace an arc using a LineBuilder
func TraceArc(t LineBuilder, x, y, rx, ry, start, angle, scale float64) {
end := start + angle
clockWise := true
if angle < 0 {
clockWise = false
}
ra := (math.Abs(rx) + math.Abs(ry)) / 2
da := math.Acos(ra/(ra+0.125/scale)) * 2
//normalize
if !clockWise {
da = -da
}
angle = start + da
var curX, curY float64
for {
if (angle < end-da/4) != clockWise {
curX = x + math.Cos(end)*rx
curY = y + math.Sin(end)*ry
break
}
curX = x + math.Cos(angle)*rx
curY = y + math.Sin(angle)*ry
angle += da
t.LineTo(curX, curY)
}
t.LineTo(curX, curY)
}