org.jogamp.glg2d.impl

Class SimplePathVisitor

java.lang.Object

org.jogamp.glg2d.impl.SimplePathVisitor

All Implemented Interfaces:

PathVisitor

Direct Known Subclasses:

AbstractTesselatorVisitor, BasicStrokeLineVisitor, FastLineVisitor, FillSimpleConvexPolygonVisitor, GL2ES2SimpleConvexFillVisitor, GL2GL3StrokeLineVisitor, SimpleOrTesselatingVisitor

public abstract class SimplePathVisitor
extends Object
implements PathVisitor

This is a fast Bézier curve implementation. I can't use OpenGL's built-in evaluators because subclasses need to do something with the points, not just pass them directly to glVertex2f. This algorithm uses forward differencing. Most of this is taken from http://www.niksula.hut.fi/~hkankaan/Homepages/bezierfast.html. I derived the implementation for the quadratic on my own, but it's simple.

Field Summary

Fields

Modifier and Type	Field and Description
static int	CURVE_STEPS Just a guess.

Constructor Summary

Constructors

Constructor and Description
SimplePathVisitor()

Method Summary

Methods

Modifier and Type	Method and Description
void	cubicTo(float[] previousVertex, float[] control) Specifies a cubic parametric curve to be drawn.
int	getNumCurveSteps() Gets the number of steps to take in a quadratic or cubic curve spline.
void	quadTo(float[] previousVertex, float[] control) Specifies a quadratic parametric curve is to be drawn.
void	setNumCurveSteps(int steps) Sets the number of steps to take in a quadratic or cubic curve spline.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.jogamp.glg2d.PathVisitor

beginPoly, closeLine, endPoly, lineTo, moveTo, setGLContext, setStroke

Field Detail

CURVE_STEPS

public static final int CURVE_STEPS

Just a guess. Would be nice to make a better guess based on what's visually acceptable.

See Also:

Constant Field Values

Constructor Detail

SimplePathVisitor

public SimplePathVisitor()

Method Detail

setNumCurveSteps

public void setNumCurveSteps(int steps)

Sets the number of steps to take in a quadratic or cubic curve spline.

getNumCurveSteps

public int getNumCurveSteps()

Gets the number of steps to take in a quadratic or cubic curve spline.

quadTo

public void quadTo(float[] previousVertex,
          float[] control)

Description copied from interface: PathVisitor

Specifies a quadratic parametric curve is to be drawn. The curve is interpolated by solving the parametric control equation in the range (t=[0..1]) using the previous point (CP), the first control point (P1), and the final interpolated control point (P2). The parametric control equation for this curve is:

          P(t) = B(2,0)*CP + B(2,1)*P1 + B(2,2)*P2
          0 <= t <= 1
 
        B(n,m) = mth coefficient of nth degree Bernstein polynomial
               = C(n,m) * t^(m) * (1 - t)^(n-m)
        C(n,m) = Combinations of n things, taken m at a time
               = n! / (m! * (n-m)!)
 

Specified by:

quadTo in interface PathVisitor

Parameters:

previousVertex - The first control point. The same as the most recent specified vertex.

control - The control point and the second vertex, in order.

cubicTo

public void cubicTo(float[] previousVertex,
           float[] control)

Description copied from interface: PathVisitor

Specifies a cubic parametric curve to be drawn. The curve is interpolated by solving the parametric control equation in the range (t=[0..1]) using the previous point (CP), the first control point (P1), the second control point (P2), and the final interpolated control point (P3). The parametric control equation for this curve is:

          P(t) = B(3,0)*CP + B(3,1)*P1 + B(3,2)*P2 + B(3,3)*P3
          0 <= t <= 1
 
        B(n,m) = mth coefficient of nth degree Bernstein polynomial
               = C(n,m) * t^(m) * (1 - t)^(n-m)
        C(n,m) = Combinations of n things, taken m at a time
               = n! / (m! * (n-m)!)
 

This form of curve is commonly known as a Bézier curve.

Specified by:

cubicTo in interface PathVisitor

Parameters:

previousVertex - The first control point. The same as the most recent specified vertex.

control - The two control points and the second vertex, in order.