WebCore/platform/graphics/Path.cpp

/*
 * Copyright (C) 2003, 2006 Apple Computer, Inc.  All rights reserved.
 *                     2006 Rob Buis <buis@kde.org>
 * Copyright (C) 2007 Eric Seidel <eric@webkit.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */


#include "config.h"
#include "Path.h"

#include "FloatPoint.h"
#include "FloatRect.h"
#include "PathTraversalState.h"
#include <math.h>
#include <wtf/MathExtras.h>

const double QUARTER = 0.552; // approximation of control point positions on a bezier
                              // to simulate a quarter of a circle.
namespace WebCore {

void pathLengthApplierFunction(void* info, const PathElement* element)
{
    PathTraversalState& traversalState = *static_cast<PathTraversalState*>(info);
    if (traversalState.m_success)
        return;
    traversalState.m_previous = traversalState.m_current;
    FloatPoint* points = element->points;
    float segmentLength = 0.0f;
    switch (element->type) {
        case PathElementMoveToPoint:
            segmentLength = traversalState.moveTo(points[0]);
            break;
        case PathElementAddLineToPoint:
            segmentLength = traversalState.lineTo(points[0]);
            break;
        case PathElementAddQuadCurveToPoint:
            segmentLength = traversalState.quadraticBezierTo(points[0], points[1]);
            break;
        case PathElementAddCurveToPoint:
            segmentLength = traversalState.cubicBezierTo(points[0], points[1], points[2]);
            break;
        case PathElementCloseSubpath:
            segmentLength = traversalState.closeSubpath();
            break;
    }
    traversalState.m_totalLength += segmentLength;
    if ((traversalState.m_action == PathTraversalState::TraversalPointAtLength)
     && (traversalState.m_totalLength > traversalState.m_desiredLength)) {
        // FIXME: Need to actually find the exact point and change m_current
        traversalState.m_success = true;
    } else if ((traversalState.m_action == PathTraversalState::TraversalNormalAngleAtLength)
           && (traversalState.m_totalLength > traversalState.m_desiredLength)) {
        FloatSize change = traversalState.m_previous - traversalState.m_current;
        // tangent slope = -1/slope = -1/yChange/xChange = -xChange/yChange; arc-tangent converts a slope into an angle
        static float rad2deg = 360 / 2 * M_PI;
        traversalState.m_normalAngle = (change.height() == 0) ? 0 : (atan2(-change.width(), change.height()) * rad2deg);
        traversalState.m_success = true;
    }
}

float Path::length()
{
    PathTraversalState traversalState(PathTraversalState::TraversalTotalLength);
    apply(&traversalState, pathLengthApplierFunction);
    return traversalState.m_totalLength;
}

FloatPoint Path::pointAtLength(float length, bool& ok)
{
    PathTraversalState traversalState(PathTraversalState::TraversalPointAtLength);
    traversalState.m_desiredLength = length;
    apply(&traversalState, pathLengthApplierFunction);
    ok = traversalState.m_success;
    return traversalState.m_current;
}

float Path::normalAngleAtLength(float length, bool& ok)
{
    PathTraversalState traversalState(PathTraversalState::TraversalNormalAngleAtLength);
    traversalState.m_desiredLength = length;
    apply(&traversalState, pathLengthApplierFunction);
    ok = traversalState.m_success;
    return traversalState.m_normalAngle;
}

Path Path::createRoundedRectangle(const FloatRect& rectangle, const FloatSize& roundingRadii)
{
    Path path;
    double x = rectangle.x();
    double y = rectangle.y();
    double width = rectangle.width();
    double height = rectangle.height();
    double rx = roundingRadii.width();
    double ry = roundingRadii.height();
    if (width <= 0.0 || height <= 0.0)
        return path;

    double dx = rx, dy = ry;
    // If rx is greater than half of the width of the rectangle
    // then set rx to half of the width (required in SVG spec)
    if (dx > width * 0.5)
        dx = width * 0.5;

    // If ry is greater than half of the height of the rectangle
    // then set ry to half of the height (required in SVG spec)
    if (dy > height * 0.5)
        dy = height * 0.5;

    path.moveTo(FloatPoint(x + dx, y));

    if (dx < width * 0.5)
        path.addLineTo(FloatPoint(x + width - rx, y));

    path.addBezierCurveTo(FloatPoint(x + width - dx * (1 - QUARTER), y), FloatPoint(x + width, y + dy * (1 - QUARTER)), FloatPoint(x + width, y + dy));

    if (dy < height * 0.5)
        path.addLineTo(FloatPoint(x + width, y + height - dy));

    path.addBezierCurveTo(FloatPoint(x + width, y + height - dy * (1 - QUARTER)), FloatPoint(x + width - dx * (1 - QUARTER), y + height), FloatPoint(x + width - dx, y + height));

    if (dx < width * 0.5)
        path.addLineTo(FloatPoint(x + dx, y + height));

    path.addBezierCurveTo(FloatPoint(x + dx * (1 - QUARTER), y + height), FloatPoint(x, y + height - dy * (1 - QUARTER)), FloatPoint(x, y + height - dy));

    if (dy < height * 0.5)
        path.addLineTo(FloatPoint(x, y + dy));

    path.addBezierCurveTo(FloatPoint(x, y + dy * (1 - QUARTER)), FloatPoint(x + dx * (1 - QUARTER), y), FloatPoint(x + dx, y));

    path.closeSubpath();

    return path;
}

Path Path::createRectangle(const FloatRect& rectangle)
{
    Path path;
    double x = rectangle.x();
    double y = rectangle.y();
    double width = rectangle.width();
    double height = rectangle.height();
    if (width < 0.0 || height < 0.0)
        return path;
    
    path.moveTo(FloatPoint(x, y));
    path.addLineTo(FloatPoint(x + width, y));
    path.addLineTo(FloatPoint(x + width, y + height));
    path.addLineTo(FloatPoint(x, y + height));
    path.closeSubpath();

    return path;
}

Path Path::createEllipse(const FloatPoint& center, float rx, float ry)
{
    double cx = center.x();
    double cy = center.y();
    Path path;
    if (rx <= 0.0 || ry <= 0.0)
        return path;

    double x = cx, y = cy;

    unsigned step = 0, num = 100;
    bool running = true;
    while (running)
    {
        if (step == num)
        {
            running = false;
            break;
        }

        double angle = double(step) / double(num) * 2.0 * M_PI;
        x = cx + cos(angle) * rx;
        y = cy + sin(angle) * ry;

        step++;
        if (step == 1)
            path.moveTo(FloatPoint(x, y));
        else
            path.addLineTo(FloatPoint(x, y));
    }

    path.closeSubpath();

    return path;
}

Path Path::createCircle(const FloatPoint& center, float r)
{
    return createEllipse(center, r, r);
}

Path Path::createLine(const FloatPoint& start, const FloatPoint& end)
{
    Path path;
    if (start.x() == end.x() && start.y() == end.y())
        return path;

    path.moveTo(start);
    path.addLineTo(end);

    return path;
}

}