我想知道Path的长度。
例如，如果我有一条直线，我可以用开始x，y和结束x，y值来计算长度。但是，如果我使用QuadCurves或CubicCurves，它会很快变得非常棘手。
有没有办法得到Path的长度或近似值？
例如以下路径：
Path path = new Path();
MoveTo moveTo = new MoveTo(start.getX(), start.getY());
double controlPointX = 50;
CubicCurveTo cubicCurveTo = new CubicCurveTo(start.getX() + controlPointX, start.getY(),
start.getX() + controlPointX, end.getY(), end.getX(), end.getY());
path.getElements().addAll(moveTo, cubicCurveTo);
答案 0 :(得分：1)
我最近也需要这个。我在网上找不到任何解决方案，但我发现PathTransition必须计算它。确实如此，请参见PathTransition.recomputeSegment，计算totalLength的位置。
不幸的是，它使用Node和PathElement中的许多内部API将Path转换为java.awt.geom.Path2D。我提取了这些方法并将com.sun类的其他用法替换为java.awt个，然后从PathTransition.recomputeSegments中提取与计算长度相关的部分。
结果代码如下。它在Kotlin而不是Java，但它应该很容易将其转换回Java。我还没有对它进行过广泛的测试，但它似乎正在研究我测试过的相当复杂的路径。我将结果与PathTransition计算的长度进行了比较，结果非常接近，我认为差异是由于我的代码使用Path2D.Double，Path2D.Float使用了PathElement.impl_addTo }}
fun Transform.toAffineTransform(): AffineTransform {
if(!isType2D) throw UnsupportedOperationException("Conversion of 3D transforms is unsupported")
return AffineTransform(mxx, myx, mxy, myy, tx, ty)
}
val Path.totalLength: Double
get() {
var length = 0.0
val coords = DoubleArray(6)
var pt = 0 // Previous segment type
var px = 0.0 // Previous x-coordinate
var py = 0.0 // Previous y-coordinate
var mx = 0.0 // Last move to x-coordinate
var my = 0.0 // Last move to y-coordinate
val pit = toPath2D().getPathIterator(localToParentTransform.toAffineTransform(), 1.0)
while(!pit.isDone) {
val type = pit.currentSegment(coords)
val x = coords[0]
val y = coords[1]
when(type) {
PathIterator.SEG_MOVETO -> {
mx = x
my = y
}
PathIterator.SEG_LINETO -> {
val dx = x - px
val dy = y - py
val l = sqrt(dx * dx + dy * dy)
if(l >= 1 || pt == PathIterator.SEG_MOVETO) length += l
}
PathIterator.SEG_CLOSE -> {
val dx = x - mx
val dy = y - my
val l = sqrt(dx * dx + dy * dy)
if(l >= 1 || pt == PathIterator.SEG_MOVETO) length += l
}
}
pt = type
px = x
py = y
pit.next()
}
return length
}
fun Path.toPath2D(): Path2D {
val path: Path2D = Path2D.Double(if(fillRule == FillRule.EVEN_ODD) Path2D.WIND_EVEN_ODD else Path2D.WIND_NON_ZERO)
for(e in elements) {
when(e) {
is Arc2D -> append(e as ArcTo, path) // Why isn't this smart casted?
is ClosePath -> path.closePath()
is CubicCurveTo -> append(e, path)
is HLineTo -> append(e, path)
is LineTo -> append(e, path)
is MoveTo -> append(e, path)
is QuadCurveTo -> append(e, path)
is VLineTo -> append(e, path)
else -> throw UnsupportedOperationException("Path contains unknown PathElement type: " + e::class.qualifiedName)
}
}
return path
}
private fun append(arcTo: ArcTo, path: Path2D) {
val x0 = path.currentPoint.x
val y0 = path.currentPoint.y
val localX = arcTo.x
val localY = arcTo.y
val localSweepFlag = arcTo.isSweepFlag
val localLargeArcFlag = arcTo.isLargeArcFlag
// Determine target "to" position
val xto = if(arcTo.isAbsolute) localX else localX + x0
val yto = if(arcTo.isAbsolute) localY else localY + y0
// Compute the half distance between the current and the final point
val dx2 = (x0 - xto) / 2.0
val dy2 = (y0 - yto) / 2.0
// Convert angle from degrees to radians
val xAxisRotationR = Math.toRadians(arcTo.xAxisRotation)
val cosAngle = Math.cos(xAxisRotationR)
val sinAngle = Math.sin(xAxisRotationR)
//
// Step 1 : Compute (x1, y1)
//
val x1 = cosAngle * dx2 + sinAngle * dy2
val y1 = -sinAngle * dx2 + cosAngle * dy2
// Ensure radii are large enough
var rx = abs(arcTo.radiusX)
var ry = abs(arcTo.radiusY)
var Prx = rx * rx
var Pry = ry * ry
val Px1 = x1 * x1
val Py1 = y1 * y1
// check that radii are large enough
val radiiCheck = Px1 / Prx + Py1 / Pry
if (radiiCheck > 1.0) {
rx *= sqrt(radiiCheck)
ry *= sqrt(radiiCheck)
if(rx == rx && ry == ry) {/* not NANs */ }
else {
path.lineTo(xto, yto)
return
}
Prx = rx * rx
Pry = ry * ry
}
//
// Step 2 : Compute (cx1, cy1)
//
var sign = if (localLargeArcFlag == localSweepFlag) -1.0 else 1.0
var sq = (Prx * Pry - Prx * Py1 - Pry * Px1) / (Prx * Py1 + Pry * Px1)
sq = if (sq < 0.0) 0.0 else sq
val coef = sign * Math.sqrt(sq)
val cx1 = coef * (rx * y1 / ry)
val cy1 = coef * -(ry * x1 / rx)
//
// Step 3 : Compute (cx, cy) from (cx1, cy1)
//
val sx2 = (x0 + xto) / 2.0
val sy2 = (y0 + yto) / 2.0
val cx = sx2 + (cosAngle * cx1 - sinAngle * cy1)
val cy = sy2 + (sinAngle * cx1 + cosAngle * cy1)
//
// Step 4 : Compute the angleStart (angle1) and the angleExtent (dangle)
//
val ux = (x1 - cx1) / rx
val uy = (y1 - cy1) / ry
val vx = (-x1 - cx1) / rx
val vy = (-y1 - cy1) / ry
// Compute the angle start
var n = sqrt(ux * ux + uy * uy)
var p = ux // (1 * ux) + (0 * uy)
sign = if (uy < 0.0) -1.0 else 1.0
var angleStart = (sign * Math.acos(p / n)).toDegrees()
// Compute the angle extent
n = Math.sqrt((ux * ux + uy * uy) * (vx * vx + vy * vy))
p = ux * vx + uy * vy
sign = if (ux * vy - uy * vx < 0.0) -1.0 else 1.0
var angleExtent = Math.toDegrees(sign * Math.acos(p / n))
if(!localSweepFlag && angleExtent > 0) angleExtent -= 360.0
else if(localSweepFlag && angleExtent < 0) angleExtent += 360.0
angleExtent %= 360
angleStart %= 360
//
// We can now build the resulting Arc2D
//
val arcX = cx - rx
val arcY = cy - ry
val arcW = rx * 2.0
val arcH = ry * 2.0
val arcStart = -angleStart
val arcExtent = -angleExtent
val arc = Arc2D.Double(OPEN).apply { setArc(arcX, arcY, arcW, arcH, arcStart, arcExtent, OPEN) }
val xform: AffineTransform? = when(xAxisRotationR) {
0.0 -> null
else -> AffineTransform().apply { setToRotation(xAxisRotationR, cx, cy) }
}
val pi = arc.getPathIterator(xform)
// RT-8926, append(true) converts the initial moveTo into a
// lineTo which can generate huge miter joins if the segment
// is small enough. So, we manually skip it here instead.
pi.next()
path.append(pi, true)
}
private fun append(cubicCurveTo: CubicCurveTo, path: Path2D) {
if(cubicCurveTo.isAbsolute) {
path.curveTo(cubicCurveTo.controlX1, cubicCurveTo.controlY1,
cubicCurveTo.controlX2, cubicCurveTo.controlY2,
cubicCurveTo.x, cubicCurveTo.y)
}
else {
val dx = path.currentPoint.x
val dy = path.currentPoint.y
path.curveTo(cubicCurveTo.controlX1 + dx, cubicCurveTo.controlY1 + dy,
cubicCurveTo.controlX2 + dx, cubicCurveTo.controlY2 + dy,
cubicCurveTo.x + dx, cubicCurveTo.y + dy)
}
}
private fun append(hLineTo: HLineTo, path: Path2D) {
if(hLineTo.isAbsolute) path.lineTo(hLineTo.x, path.currentPoint.y)
else path.lineTo(path.currentPoint.x + hLineTo.x, path.currentPoint.y)
}
private fun append(lineTo: LineTo, path: Path2D) {
if(lineTo.isAbsolute) path.lineTo(lineTo.x, lineTo.y)
else path.lineTo(path.currentPoint.x + lineTo.x, path.currentPoint.y + lineTo.y)
}
private fun append(moveTo: MoveTo, path: Path2D) {
if(moveTo.isAbsolute) path.moveTo(moveTo.x, moveTo.y)
else path.moveTo((path.currentPoint.x + moveTo.x), path.currentPoint.y + moveTo.y)
}
private fun append(quadCurveTo: QuadCurveTo, path: Path2D) {
if(quadCurveTo.isAbsolute) {
path.quadTo(quadCurveTo.controlX, quadCurveTo.controlY,
quadCurveTo.x, quadCurveTo.y)
}
else {
val dx = path.currentPoint.x
val dy = path.currentPoint.y
path.quadTo(quadCurveTo.controlX + dx, quadCurveTo.controlY + dy,
quadCurveTo.x + dx, quadCurveTo.y + dy)
}
}
private fun append(vLineTo: VLineTo, path: Path2D) {
if(vLineTo.isAbsolute) path.lineTo(path.currentPoint.x, vLineTo.y)
else path.lineTo(path.currentPoint.x, path.currentPoint.y + vLineTo.y)
}