draw2d/curve/quad_float64.go
2015-04-22 19:07:03 +02:00

61 lines
1.5 KiB
Go

// Copyright 2010 The draw2d Authors. All rights reserved.
// created: 17/05/2011 by Laurent Le Goff
package curve
import (
"math"
)
//x1, y1, cpx1, cpy2, x2, y2 float64
type QuadCurveFloat64 [6]float64
// Subdivide a Bezier quad curve in 2 equivalents Bezier quad curves.
// c1 and c2 parameters are the resulting curves
func (c *QuadCurveFloat64) Subdivide(c1, c2 *QuadCurveFloat64) {
// First point of c is the first point of c1
c1[0], c1[1] = c[0], c[1]
// Last point of c is the last point of c2
c2[4], c2[5] = c[4], c[5]
// Subdivide segment using midpoints
c1[2] = (c[0] + c[2]) / 2
c1[3] = (c[1] + c[3]) / 2
c2[2] = (c[2] + c[4]) / 2
c2[3] = (c[3] + c[5]) / 2
c1[4] = (c1[2] + c2[2]) / 2
c1[5] = (c1[3] + c2[3]) / 2
c2[0], c2[1] = c1[4], c1[5]
return
}
// Trace generate lines subdividing the curve using a LineTracer
// flattening_threshold helps determines the flattening expectation of the curve
func (curve *QuadCurveFloat64) Trace(t LineTracer, flattening_threshold float64) {
// Allocates curves stack
var curves [CurveRecursionLimit]QuadCurveFloat64
curves[0] = *curve
i := 0
// current curve
var c *QuadCurveFloat64
var dx, dy, d float64
for i >= 0 {
c = &curves[i]
dx = c[4] - c[0]
dy = c[5] - c[1]
d = math.Abs(((c[2]-c[4])*dy - (c[3]-c[5])*dx))
// if it's flat then trace a line
if (d*d) < flattening_threshold*(dx*dx+dy*dy) || i == len(curves)-1 {
t.LineTo(c[4], c[5])
i--
} else {
// second half of bezier go lower onto the stack
c.Subdivide(&curves[i+1], &curves[i])
i++
}
}
}