msdfgen/core/edge-segments.h

#pragma once

#include "Vector2.h"
#include "SignedDistance.h"
#include "EdgeColor.h"

namespace msdfgen {

// Parameters for iterative search of closest point on a cubic Bezier curve. Increase for higher precision.
#define MSDFGEN_CUBIC_SEARCH_STARTS 4
#define MSDFGEN_CUBIC_SEARCH_STEPS 4

// Threshold of the dot product of adjacent edge directions to be considered convergent.
#define MSDFGEN_CORNER_DOT_EPSILON 0.000001

/// An abstract edge segment.
class EdgeSegment {

public:
    EdgeColor color;

    EdgeSegment(EdgeColor edgeColor = WHITE) : color(edgeColor) { }
    virtual ~EdgeSegment() { }
    /// Creates a copy of the edge segment.
    virtual EdgeSegment * clone() const = 0;
    /// Returns the point on the edge specified by the parameter (between 0 and 1).
    virtual Point2 point(double param) const = 0;
    /// Returns the direction the edge has at the point specified by the parameter.
    virtual Vector2 direction(double param) const = 0;
    /// Returns the change of direction (second derivative) at the point specified by the parameter.
    virtual Vector2 directionChange(double param) const = 0;
    /// Returns the direction tendency vector that can resolve cases where directions converge at a corner.
    virtual Vector2 directionTendency(double param, int polarity) const;
    /// Returns the minimum signed distance between origin and the edge.
    virtual SignedDistance signedDistance(Point2 origin, double &param) const = 0;
    /// Converts a previously retrieved signed distance from origin to pseudo-distance.
    virtual void distanceToPseudoDistance(SignedDistance &distance, Point2 origin, double param) const;
    /// Outputs a list of (at most three) intersections (their X coordinates) with an infinite horizontal scanline at y and returns how many there are.
    virtual int scanlineIntersections(double x[3], int dy[3], double y) const = 0;
    /// Adjusts the bounding box to fit the edge segment.
    virtual void bound(double &l, double &b, double &r, double &t) const = 0;

    /// Moves the start point of the edge segment.
    virtual void moveStartPoint(Point2 to) = 0;
    /// Moves the end point of the edge segment.
    virtual void moveEndPoint(Point2 to) = 0;
    /// Splits the edge segments into thirds which together represent the original edge.
    virtual void splitInThirds(EdgeSegment *&part1, EdgeSegment *&part2, EdgeSegment *&part3) const = 0;
    /// Converts convergent segment to a divergent segment. If NULL is returned, the object is already divergent and has been updated.
    virtual EdgeSegment * makeDivergent(int dStart, int dEnd) = 0;

};

/// A line segment.
class LinearSegment : public EdgeSegment {

public:
    Point2 p[2];

    LinearSegment(Point2 p0, Point2 p1, EdgeColor edgeColor = WHITE);
    LinearSegment * clone() const;
    Point2 point(double param) const;
    Vector2 direction(double param) const;
    Vector2 directionChange(double param) const;
    SignedDistance signedDistance(Point2 origin, double &param) const;
    int scanlineIntersections(double x[3], int dy[3], double y) const;
    void bound(double &l, double &b, double &r, double &t) const;

    void moveStartPoint(Point2 to);
    void moveEndPoint(Point2 to);
    void splitInThirds(EdgeSegment *&part1, EdgeSegment *&part2, EdgeSegment *&part3) const;
    EdgeSegment * makeDivergent(int dStart, int dEnd);

};

/// A quadratic Bezier curve.
class QuadraticSegment : public EdgeSegment {

public:
    Point2 p[3];

    QuadraticSegment(Point2 p0, Point2 p1, Point2 p2, EdgeColor edgeColor = WHITE);
    QuadraticSegment * clone() const;
    Point2 point(double param) const;
    Vector2 direction(double param) const;
    Vector2 directionChange(double param) const;
    SignedDistance signedDistance(Point2 origin, double &param) const;
    int scanlineIntersections(double x[3], int dy[3], double y) const;
    void bound(double &l, double &b, double &r, double &t) const;

    void moveStartPoint(Point2 to);
    void moveEndPoint(Point2 to);
    void splitInThirds(EdgeSegment *&part1, EdgeSegment *&part2, EdgeSegment *&part3) const;
    EdgeSegment * makeDivergent(int dStart, int dEnd);

};

/// A cubic Bezier curve.
class CubicSegment : public EdgeSegment {

public:
    Point2 p[4];

    CubicSegment(Point2 p0, Point2 p1, Point2 p2, Point2 p3, EdgeColor edgeColor = WHITE);
    CubicSegment * clone() const;
    Point2 point(double param) const;
    Vector2 direction(double param) const;
    Vector2 directionChange(double param) const;
    SignedDistance signedDistance(Point2 origin, double &param) const;
    int scanlineIntersections(double x[3], int dy[3], double y) const;
    void bound(double &l, double &b, double &r, double &t) const;

    void moveStartPoint(Point2 to);
    void moveEndPoint(Point2 to);
    void splitInThirds(EdgeSegment *&part1, EdgeSegment *&part2, EdgeSegment *&part3) const;
    EdgeSegment * makeDivergent(int dStart, int dEnd);

};

template <class BaseSegment>
class DivergentEdgeSegment : public BaseSegment {

public:
    int dStart, dEnd;

    explicit DivergentEdgeSegment(const BaseSegment &base, int dStart, int dEnd);
    SignedDistance signedDistance(Point2 origin, double &param) const;
    void distanceToPseudoDistance(SignedDistance &distance, Point2 origin, double param) const;
    EdgeSegment * makeDivergent(int dStart, int dEnd);

};

}