FlatteningPathIterator

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java.awt.geom
Class FlatteningPathIterator

java.lang.Object
  java.awt.geom.FlatteningPathIterator

All Implemented Interfaces:: PathIterator

public class FlatteningPathIterator
extends java.lang.Object
implements PathIterator

A PathIterator for approximating curved path segments by sequences of straight lines. Instances of this class will only return segments of type PathIterator.SEG_MOVETO 55 , PathIterator.SEG_LINETO 55 , and PathIterator.SEG_CLOSE 55 .

The accuracy of the approximation is determined by two parameters:

The flatness is a threshold value for deciding when a curved segment is consided flat enough for being approximated by a single straight line. Flatness is defined as the maximal distance of a curve control point to the straight line that connects the curve start and end. A lower flatness threshold means a closer approximation. See QuadCurve2D.getFlatness() 55 and CubicCurve2D.getFlatness() 55 for drawings which illustrate the meaning of flatness.
The recursion limit imposes an upper bound for how often a curved segment gets subdivided. A limit of n means that for each individual quadratic and cubic Bézier spline segment, at most 2ⁿ PathIterator.SEG_LINETO 55 segments will be created.

Memory Efficiency: The memory consumption grows linearly with the recursion limit. Neither the flatness parameter nor the number of segments in the flattened path will affect the memory consumption.

Thread Safety: Multiple threads can safely work on separate instances of this class. However, multiple threads should not concurrently access the same instance, as no synchronization is performed.

Since:: 1.2

Field Summary

private boolean done
          A flag that indicates when this path iterator has finished its iteration over path segments.

private double flatnessSq
          The square of the flatness threshold value, which determines when a curve segment is considered flat enough that no further subdivision is needed.

private int[] recLevel
          The number of recursions that were performed to arrive at a segment on the stack.

private int recursionLimit
          The maximal number of subdivions that are performed to approximate a quadratic or cubic curve segment.

private double[] scratch


private PathIterator srcIter
          The PathIterator whose curved segments are being approximated.

private double srcPosX
          The current x position of the source iterator.

private double srcPosY
          The current y position of the source iterator.

private int srcSegType
          The segment type of the last segment that was returned by the source iterator.

private double[] stack
          A stack for holding the coordinates of subdivided segments.

private int stackSize
          The current stack size.

Fields inherited from interface java.awt.geom.PathIterator

SEG_CLOSE, SEG_CUBICTO, SEG_LINETO, SEG_MOVETO, SEG_QUADTO, WIND_EVEN_ODD, WIND_NON_ZERO

Constructor Summary

FlatteningPathIterator(PathIterator src, double flatness)
          Constructs a new PathIterator for approximating an input PathIterator with straight lines.

FlatteningPathIterator(PathIterator src, double flatness, int limit)
          Constructs a new PathIterator for approximating an input PathIterator with straight lines.

Method Summary

int currentSegment(double[] coords)
          Returns the coordinates of the next point(s), as well as the type of line segment.

int currentSegment(float[] coords)
          Returns the coordinates of the next point(s), as well as the type of line segment.

private void fetchSegment()
          Fetches the next segment from the source iterator.

double getFlatness()
          Returns the maximally acceptable flatness.

int getRecursionLimit()
          Returns the maximum number of recursive curve subdivisions.

int getWindingRule()
          Returns the winding rule to determine which points are inside this path.

boolean isDone()
          Tests if the iterator is exhausted.

void next()
          Advance to the next segment in the iteration.

private void subdivideCubic()
          Repeatedly subdivides the cubic curve segment that is on top of the stack.

private void subdivideQuadratic()
          Repeatedly subdivides the quadratic curve segment that is on top of the stack.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

srcIter

private final PathIterator srcIter

The PathIterator whose curved segments are being approximated.

flatnessSq

private final double flatnessSq

The square of the flatness threshold value, which determines when a curve segment is considered flat enough that no further subdivision is needed.

Calculating flatness actually produces the squared flatness value. To avoid the relatively expensive calculation of a square root for each curve segment, we perform all flatness comparisons on squared values.

See Also:: QuadCurve2D.getFlatnessSq() 55 , CubicCurve2D.getFlatnessSq() 55

recursionLimit

private final int recursionLimit

The maximal number of subdivions that are performed to approximate a quadratic or cubic curve segment.

stack

private double[] stack

A stack for holding the coordinates of subdivided segments.

See Also:: Implementation Note

stackSize

private int stackSize

The current stack size.

See Also:: Implementation Note

recLevel

private int[] recLevel

The number of recursions that were performed to arrive at a segment on the stack.

See Also:: Implementation Note

scratch

private final double[] scratch

srcSegType

private int srcSegType

The segment type of the last segment that was returned by the source iterator.

srcPosX

private double srcPosX

The current x position of the source iterator.

srcPosY

private double srcPosY

The current y position of the source iterator.

done

private boolean done

A flag that indicates when this path iterator has finished its iteration over path segments.

Constructor Detail

FlatteningPathIterator

public FlatteningPathIterator(PathIterator src,
                              double flatness)

Constructs a new PathIterator for approximating an input PathIterator with straight lines. The approximation works by recursive subdivisons, until the specified flatness threshold is not exceeded.

There will not be more than 10 nested recursion steps, which means that a single SEG_QUADTO or SEG_CUBICTO segment is approximated by at most 2¹⁰ = 1024 straight lines.

FlatteningPathIterator

public FlatteningPathIterator(PathIterator src,
                              double flatness,
                              int limit)

Constructs a new PathIterator for approximating an input PathIterator with straight lines. The approximation works by recursive subdivisons, until the specified flatness threshold is not exceeded. Additionally, the number of recursions is also bound by the specified recursion limit.

Method Detail

getFlatness

public double getFlatness()

Returns the maximally acceptable flatness.

getRecursionLimit

public int getRecursionLimit()

Returns the maximum number of recursive curve subdivisions.