JUCE/modules/juce_graphics/geometry/juce_Line.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2013 - Raw Material Software Ltd.

   Permission is granted to use this software under the terms of either:
   a) the GPL v2 (or any later version)
   b) the Affero GPL v3

   Details of these licenses can be found at: www.gnu.org/licenses

   JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

   ------------------------------------------------------------------------------

   To release a closed-source product which uses JUCE, commercial licenses are
   available: visit www.juce.com for more information.

  ==============================================================================
*/

#ifndef JUCE_LINE_H_INCLUDED
#define JUCE_LINE_H_INCLUDED


//==============================================================================
/**
    Represents a line.

    This class contains a bunch of useful methods for various geometric
    tasks.

    The ValueType template parameter should be a primitive type - float or double
    are what it's designed for. Integer types will work in a basic way, but some methods
    that perform mathematical operations may not compile, or they may not produce
    sensible results.

    @see Point, Rectangle, Path, Graphics::drawLine
*/
template <typename ValueType>
class Line
{
public:
    //==============================================================================
    /** Creates a line, using (0, 0) as its start and end points. */
    Line() noexcept {}

    /** Creates a copy of another line. */
    Line (const Line& other) noexcept
        : start (other.start),
          end (other.end)
    {
    }

    /** Creates a line based on the coordinates of its start and end points. */
    Line (ValueType startX, ValueType startY, ValueType endX, ValueType endY) noexcept
        : start (startX, startY),
          end (endX, endY)
    {
    }

    /** Creates a line from its start and end points. */
    Line (const Point<ValueType> startPoint,
          const Point<ValueType> endPoint) noexcept
        : start (startPoint),
          end (endPoint)
    {
    }

    /** Copies a line from another one. */
    Line& operator= (const Line& other) noexcept
    {
        start = other.start;
        end = other.end;
        return *this;
    }

    /** Destructor. */
    ~Line() noexcept {}

    //==============================================================================
    /** Returns the x coordinate of the line's start point. */
    inline ValueType getStartX() const noexcept                             { return start.x; }

    /** Returns the y coordinate of the line's start point. */
    inline ValueType getStartY() const noexcept                             { return start.y; }

    /** Returns the x coordinate of the line's end point. */
    inline ValueType getEndX() const noexcept                               { return end.x; }

    /** Returns the y coordinate of the line's end point. */
    inline ValueType getEndY() const noexcept                               { return end.y; }

    /** Returns the line's start point. */
    inline Point<ValueType> getStart() const noexcept                       { return start; }

    /** Returns the line's end point. */
    inline Point<ValueType> getEnd() const noexcept                         { return end; }

    /** Changes this line's start point */
    void setStart (ValueType newStartX, ValueType newStartY) noexcept       { start.setXY (newStartX, newStartY); }

    /** Changes this line's end point */
    void setEnd (ValueType newEndX, ValueType newEndY) noexcept             { end.setXY (newEndX, newEndY); }

    /** Changes this line's start point */
    void setStart (const Point<ValueType> newStart) noexcept                { start = newStart; }

    /** Changes this line's end point */
    void setEnd (const Point<ValueType> newEnd) noexcept                    { end = newEnd; }

    /** Returns a line that is the same as this one, but with the start and end reversed, */
    const Line reversed() const noexcept                                    { return Line (end, start); }

    /** Applies an affine transform to the line's start and end points. */
    void applyTransform (const AffineTransform& transform) noexcept
    {
        start.applyTransform (transform);
        end.applyTransform (transform);
    }

    //==============================================================================
    /** Returns the length of the line. */
    ValueType getLength() const noexcept                                    { return start.getDistanceFrom (end); }

    /** Returns true if the line's start and end x coordinates are the same. */
    bool isVertical() const noexcept                                        { return start.x == end.x; }

    /** Returns true if the line's start and end y coordinates are the same. */
    bool isHorizontal() const noexcept                                      { return start.y == end.y; }

    /** Returns the line's angle.

        This value is the number of radians clockwise from the 12 o'clock direction,
        where the line's start point is considered to be at the centre.
    */
    typename Point<ValueType>::FloatType getAngle() const noexcept          { return start.getAngleToPoint (end); }

    /** Casts this line to float coordinates. */
    Line<float> toFloat() const noexcept                                    { return Line<float> (start.toFloat(), end.toFloat()); }

    /** Casts this line to double coordinates. */
    Line<double> toDouble() const noexcept                                  { return Line<double> (start.toDouble(), end.toDouble()); }

    //==============================================================================
    /** Compares two lines. */
    bool operator== (const Line& other) const noexcept                      { return start == other.start && end == other.end; }

    /** Compares two lines. */
    bool operator!= (const Line& other) const noexcept                      { return start != other.start || end != other.end; }

    //==============================================================================
    /** Finds the intersection between two lines.

        @param line     the line to intersect with
        @returns        the point at which the lines intersect, even if this lies beyond the end of the lines
    */
    Point<ValueType> getIntersection (const Line& line) const noexcept
    {
        Point<ValueType> p;
        findIntersection (start, end, line.start, line.end, p);
        return p;
    }

    /** Finds the intersection between two lines.

        @param line             the other line
        @param intersection     the position of the point where the lines meet (or
                                where they would meet if they were infinitely long)
                                the intersection (if the lines intersect). If the lines
                                are parallel, this will just be set to the position
                                of one of the line's endpoints.
        @returns    true if the line segments intersect; false if they dont. Even if they
                    don't intersect, the intersection coordinates returned will still
                    be valid
    */
    bool intersects (const Line& line, Point<ValueType>& intersection) const noexcept
    {
        return findIntersection (start, end, line.start, line.end, intersection);
    }

    /** Returns true if this line intersects another. */
    bool intersects (const Line& other) const noexcept
    {
        Point<ValueType> ignored;
        return findIntersection (start, end, other.start, other.end, ignored);
    }

    //==============================================================================
    /** Returns the location of the point which is a given distance along this line.

        @param distanceFromStart    the distance to move along the line from its
                                    start point. This value can be negative or longer
                                    than the line itself
        @see getPointAlongLineProportionally
    */
    Point<ValueType> getPointAlongLine (ValueType distanceFromStart) const noexcept
    {
        return start + (end - start) * (distanceFromStart / getLength());
    }

    /** Returns a point which is a certain distance along and to the side of this line.

        This effectively moves a given distance along the line, then another distance
        perpendicularly to this, and returns the resulting position.

        @param distanceFromStart    the distance to move along the line from its
                                    start point. This value can be negative or longer
                                    than the line itself
        @param perpendicularDistance    how far to move sideways from the line. If you're
                                    looking along the line from its start towards its
                                    end, then a positive value here will move to the
                                    right, negative value move to the left.
    */
    Point<ValueType> getPointAlongLine (ValueType distanceFromStart,
                                        ValueType perpendicularDistance) const noexcept
    {
        const Point<ValueType> delta (end - start);
        const double length = juce_hypot ((double) delta.x,
                                          (double) delta.y);
        if (length <= 0)
            return start;

        return Point<ValueType> (start.x + static_cast<ValueType> ((delta.x * distanceFromStart - delta.y * perpendicularDistance) / length),
                                 start.y + static_cast<ValueType> ((delta.y * distanceFromStart + delta.x * perpendicularDistance) / length));
    }

    /** Returns the location of the point which is a given distance along this line
        proportional to the line's length.

        @param proportionOfLength   the distance to move along the line from its
                                    start point, in multiples of the line's length.
                                    So a value of 0.0 will return the line's start point
                                    and a value of 1.0 will return its end point. (This value
                                    can be negative or greater than 1.0).
        @see getPointAlongLine
    */
    Point<ValueType> getPointAlongLineProportionally (ValueType proportionOfLength) const noexcept
    {
        return start + (end - start) * proportionOfLength;
    }

    /** Returns the smallest distance between this line segment and a given point.

        So if the point is close to the line, this will return the perpendicular
        distance from the line; if the point is a long way beyond one of the line's
        end-point's, it'll return the straight-line distance to the nearest end-point.

        pointOnLine receives the position of the point that is found.

        @returns the point's distance from the line
        @see getPositionAlongLineOfNearestPoint
    */
    ValueType getDistanceFromPoint (const Point<ValueType> targetPoint,
                                    Point<ValueType>& pointOnLine) const noexcept
    {
        const Point<ValueType> delta (end - start);
        const double length = delta.x * delta.x + delta.y * delta.y;

        if (length > 0)
        {
            const double prop = ((targetPoint.x - start.x) * delta.x
                               + (targetPoint.y - start.y) * delta.y) / length;

            if (prop >= 0 && prop <= 1.0)
            {
                pointOnLine = start + delta * static_cast<ValueType> (prop);
                return targetPoint.getDistanceFrom (pointOnLine);
            }
        }

        const float fromStart = targetPoint.getDistanceFrom (start);
        const float fromEnd = targetPoint.getDistanceFrom (end);

        if (fromStart < fromEnd)
        {
            pointOnLine = start;
            return fromStart;
        }
        else
        {
            pointOnLine = end;
            return fromEnd;
        }
    }

    /** Finds the point on this line which is nearest to a given point, and
        returns its position as a proportional position along the line.

        @returns    a value 0 to 1.0 which is the distance along this line from the
                    line's start to the point which is nearest to the point passed-in. To
                    turn this number into a position, use getPointAlongLineProportionally().
        @see getDistanceFromPoint, getPointAlongLineProportionally
    */
    ValueType findNearestProportionalPositionTo (const Point<ValueType> point) const noexcept
    {
        const Point<ValueType> delta (end - start);
        const double length = delta.x * delta.x + delta.y * delta.y;

        return length <= 0 ? 0
                           : jlimit (ValueType(), static_cast<ValueType> (1),
                                     static_cast<ValueType> ((((point.x - start.x) * delta.x
                                                             + (point.y - start.y) * delta.y) / length)));
    }

    /** Finds the point on this line which is nearest to a given point.
        @see getDistanceFromPoint, findNearestProportionalPositionTo
    */
    Point<ValueType> findNearestPointTo (const Point<ValueType> point) const noexcept
    {
        return getPointAlongLineProportionally (findNearestProportionalPositionTo (point));
    }

    /** Returns true if the given point lies above this line.

        The return value is true if the point's y coordinate is less than the y
        coordinate of this line at the given x (assuming the line extends infinitely
        in both directions).
    */
    bool isPointAbove (const Point<ValueType> point) const noexcept
    {
        return start.x != end.x
                && point.y < ((end.y - start.y)
                                    * (point.x - start.x)) / (end.x - start.x) + start.y;
    }

    //==============================================================================
    /** Returns a shortened copy of this line.

        This will chop off part of the start of this line by a certain amount, (leaving the
        end-point the same), and return the new line.
    */
    Line withShortenedStart (ValueType distanceToShortenBy) const noexcept
    {
        return Line (getPointAlongLine (jmin (distanceToShortenBy, getLength())), end);
    }

    /** Returns a shortened copy of this line.

        This will chop off part of the end of this line by a certain amount, (leaving the
        start-point the same), and return the new line.
    */
    Line withShortenedEnd (ValueType distanceToShortenBy) const noexcept
    {
        const ValueType length = getLength();
        return Line (start, getPointAlongLine (length - jmin (distanceToShortenBy, length)));
    }

private:
    //==============================================================================
    Point<ValueType> start, end;

    static bool findIntersection (const Point<ValueType> p1, const Point<ValueType> p2,
                                  const Point<ValueType> p3, const Point<ValueType> p4,
                                  Point<ValueType>& intersection) noexcept
    {
        if (p2 == p3)
        {
            intersection = p2;
            return true;
        }

        const Point<ValueType> d1 (p2 - p1);
        const Point<ValueType> d2 (p4 - p3);
        const ValueType divisor = d1.x * d2.y - d2.x * d1.y;

        if (divisor == 0)
        {
            if (! (d1.isOrigin() || d2.isOrigin()))
            {
                if (d1.y == 0 && d2.y != 0)
                {
                    const ValueType along = (p1.y - p3.y) / d2.y;
                    intersection = p1.withX (p3.x + along * d2.x);
                    return along >= 0 && along <= static_cast<ValueType> (1);
                }
                else if (d2.y == 0 && d1.y != 0)
                {
                    const ValueType along = (p3.y - p1.y) / d1.y;
                    intersection = p3.withX (p1.x + along * d1.x);
                    return along >= 0 && along <= static_cast<ValueType> (1);
                }
                else if (d1.x == 0 && d2.x != 0)
                {
                    const ValueType along = (p1.x - p3.x) / d2.x;
                    intersection = p1.withY (p3.y + along * d2.y);
                    return along >= 0 && along <= static_cast<ValueType> (1);
                }
                else if (d2.x == 0 && d1.x != 0)
                {
                    const ValueType along = (p3.x - p1.x) / d1.x;
                    intersection = p3.withY (p1.y + along * d1.y);
                    return along >= 0 && along <= static_cast<ValueType> (1);
                }
            }

            intersection = (p2 + p3) / static_cast<ValueType> (2);
            return false;
        }

        const ValueType along1 = ((p1.y - p3.y) * d2.x - (p1.x - p3.x) * d2.y) / divisor;
        intersection = p1 + d1 * along1;

        if (along1 < 0 || along1 > static_cast<ValueType> (1))
            return false;

        const ValueType along2 = ((p1.y - p3.y) * d1.x - (p1.x - p3.x) * d1.y) / divisor;
        return along2 >= 0 && along2 <= static_cast<ValueType> (1);
    }
};


#endif   // JUCE_LINE_H_INCLUDED