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