path: root/dom/svg/SVGPathSegUtils.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef DOM_SVG_SVGPATHSEGUTILS_H_
#define DOM_SVG_SVGPATHSEGUTILS_H_

#include "mozilla/ArrayUtils.h"
#include "mozilla/dom/SVGPathSegBinding.h"
#include "mozilla/gfx/Point.h"
#include "nsDebug.h"

namespace mozilla {

#define NS_SVG_PATH_SEG_MAX_ARGS 7
#define NS_SVG_PATH_SEG_FIRST_VALID_TYPE \
  dom::SVGPathSeg_Binding::PATHSEG_CLOSEPATH
#define NS_SVG_PATH_SEG_LAST_VALID_TYPE \
  dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL
#define NS_SVG_PATH_SEG_TYPE_COUNT (NS_SVG_PATH_SEG_LAST_VALID_TYPE + 1)

/**
 * Code that works with path segments can use an instance of this class to
 * store/provide information about the start of the current subpath and the
 * last path segment (if any).
 */
struct SVGPathTraversalState {
  using Point = gfx::Point;

  enum TraversalMode { eUpdateAll, eUpdateOnlyStartAndCurrentPos };

  SVGPathTraversalState()
      : start(0.0, 0.0),
        pos(0.0, 0.0),
        cp1(0.0, 0.0),
        cp2(0.0, 0.0),
        length(0.0),
        mode(eUpdateAll) {}

  bool ShouldUpdateLengthAndControlPoints() { return mode == eUpdateAll; }

  Point start;  // start point of current sub path (reset each moveto)

  Point pos;  // current position (end point of previous segment)

  Point cp1;  // quadratic control point - if the previous segment was a
              // quadratic bezier curve then this is set to the absolute
              // position of its control point, otherwise its set to pos

  Point cp2;  // cubic control point - if the previous segment was a cubic
              // bezier curve then this is set to the absolute position of
              // its second control point, otherwise it's set to pos

  float length;  // accumulated path length

  TraversalMode mode;  // indicates what to track while traversing a path
};

/**
 * This class is just a collection of static methods - it doesn't have any data
 * members, and it's not possible to create instances of this class. This class
 * exists purely as a convenient place to gather together a bunch of methods
 * related to manipulating and answering questions about path segments.
 * Internally we represent path segments purely as an array of floats. See the
 * comment documenting SVGPathData for more info on that.
 *
 * The DOM wrapper classes for encoded path segments (data contained in
 * instances of SVGPathData) is DOMSVGPathSeg and its sub-classes. Note that
 * there are multiple different DOM classes for path segs - one for each of the
 * 19 SVG 1.1 segment types.
 */
class SVGPathSegUtils {
 private:
  SVGPathSegUtils() = default;  // private to prevent instances

 public:
  static void GetValueAsString(const float* aSeg, nsAString& aValue);

  /**
   * Encode a segment type enum to a float.
   *
   * At some point in the future we will likely want to encode other
   * information into the float, such as whether the command was explicit or
   * not. For now all this method does is save on int to float runtime
   * conversion by requiring uint32_t and float to be of the same size so we
   * can simply do a bitwise uint32_t<->float copy.
   */
  static float EncodeType(uint32_t aType) {
    static_assert(sizeof(uint32_t) == sizeof(float),
                  "sizeof uint32_t and float must be the same");
    MOZ_ASSERT(IsValidType(aType), "Seg type not recognized");
    return *(reinterpret_cast<float*>(&aType));
  }

  static uint32_t DecodeType(float aType) {
    static_assert(sizeof(uint32_t) == sizeof(float),
                  "sizeof uint32_t and float must be the same");
    uint32_t type = *(reinterpret_cast<uint32_t*>(&aType));
    MOZ_ASSERT(IsValidType(type), "Seg type not recognized");
    return type;
  }

  static char16_t GetPathSegTypeAsLetter(uint32_t aType) {
    MOZ_ASSERT(IsValidType(aType), "Seg type not recognized");

    static const char16_t table[] = {
        char16_t('x'),  //  0 == PATHSEG_UNKNOWN
        char16_t('z'),  //  1 == PATHSEG_CLOSEPATH
        char16_t('M'),  //  2 == PATHSEG_MOVETO_ABS
        char16_t('m'),  //  3 == PATHSEG_MOVETO_REL
        char16_t('L'),  //  4 == PATHSEG_LINETO_ABS
        char16_t('l'),  //  5 == PATHSEG_LINETO_REL
        char16_t('C'),  //  6 == PATHSEG_CURVETO_CUBIC_ABS
        char16_t('c'),  //  7 == PATHSEG_CURVETO_CUBIC_REL
        char16_t('Q'),  //  8 == PATHSEG_CURVETO_QUADRATIC_ABS
        char16_t('q'),  //  9 == PATHSEG_CURVETO_QUADRATIC_REL
        char16_t('A'),  // 10 == PATHSEG_ARC_ABS
        char16_t('a'),  // 11 == PATHSEG_ARC_REL
        char16_t('H'),  // 12 == PATHSEG_LINETO_HORIZONTAL_ABS
        char16_t('h'),  // 13 == PATHSEG_LINETO_HORIZONTAL_REL
        char16_t('V'),  // 14 == PATHSEG_LINETO_VERTICAL_ABS
        char16_t('v'),  // 15 == PATHSEG_LINETO_VERTICAL_REL
        char16_t('S'),  // 16 == PATHSEG_CURVETO_CUBIC_SMOOTH_ABS
        char16_t('s'),  // 17 == PATHSEG_CURVETO_CUBIC_SMOOTH_REL
        char16_t('T'),  // 18 == PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS
        char16_t('t')   // 19 == PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL
    };
    static_assert(MOZ_ARRAY_LENGTH(table) == NS_SVG_PATH_SEG_TYPE_COUNT,
                  "Unexpected table size");

    return table[aType];
  }

  static uint32_t ArgCountForType(uint32_t aType) {
    MOZ_ASSERT(IsValidType(aType), "Seg type not recognized");

    static const uint8_t table[] = {
        0,  //  0 == PATHSEG_UNKNOWN
        0,  //  1 == PATHSEG_CLOSEPATH
        2,  //  2 == PATHSEG_MOVETO_ABS
        2,  //  3 == PATHSEG_MOVETO_REL
        2,  //  4 == PATHSEG_LINETO_ABS
        2,  //  5 == PATHSEG_LINETO_REL
        6,  //  6 == PATHSEG_CURVETO_CUBIC_ABS
        6,  //  7 == PATHSEG_CURVETO_CUBIC_REL
        4,  //  8 == PATHSEG_CURVETO_QUADRATIC_ABS
        4,  //  9 == PATHSEG_CURVETO_QUADRATIC_REL
        7,  // 10 == PATHSEG_ARC_ABS
        7,  // 11 == PATHSEG_ARC_REL
        1,  // 12 == PATHSEG_LINETO_HORIZONTAL_ABS
        1,  // 13 == PATHSEG_LINETO_HORIZONTAL_REL
        1,  // 14 == PATHSEG_LINETO_VERTICAL_ABS
        1,  // 15 == PATHSEG_LINETO_VERTICAL_REL
        4,  // 16 == PATHSEG_CURVETO_CUBIC_SMOOTH_ABS
        4,  // 17 == PATHSEG_CURVETO_CUBIC_SMOOTH_REL
        2,  // 18 == PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS
        2   // 19 == PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL
    };
    static_assert(MOZ_ARRAY_LENGTH(table) == NS_SVG_PATH_SEG_TYPE_COUNT,
                  "Unexpected table size");

    return table[aType];
  }

  /**
   * Convenience so that callers can pass a float containing an encoded type
   * and have it decoded implicitly.
   */
  static uint32_t ArgCountForType(float aType) {
    return ArgCountForType(DecodeType(aType));
  }

  static bool IsValidType(uint32_t aType) {
    return aType >= NS_SVG_PATH_SEG_FIRST_VALID_TYPE &&
           aType <= NS_SVG_PATH_SEG_LAST_VALID_TYPE;
  }

  static bool IsCubicType(uint32_t aType) {
    return aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_CUBIC_REL ||
           aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_CUBIC_ABS ||
           aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_CUBIC_SMOOTH_REL ||
           aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_CUBIC_SMOOTH_ABS;
  }

  static bool IsQuadraticType(uint32_t aType) {
    return aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_REL ||
           aType == dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_ABS ||
           aType ==
               dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL ||
           aType ==
               dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_ABS;
  }

  static bool IsArcType(uint32_t aType) {
    return aType == dom::SVGPathSeg_Binding::PATHSEG_ARC_ABS ||
           aType == dom::SVGPathSeg_Binding::PATHSEG_ARC_REL;
  }

  static bool IsRelativeOrAbsoluteType(uint32_t aType) {
    MOZ_ASSERT(IsValidType(aType), "Seg type not recognized");

    // When adding a new path segment type, ensure that the returned condition
    // below is still correct.
    static_assert(
        NS_SVG_PATH_SEG_LAST_VALID_TYPE ==
            dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL,
        "Unexpected type");

    return aType >= dom::SVGPathSeg_Binding::PATHSEG_MOVETO_ABS;
  }

  static bool IsRelativeType(uint32_t aType) {
    MOZ_ASSERT(IsRelativeOrAbsoluteType(aType),
               "IsRelativeType called with segment type that does not come in "
               "relative and absolute forms");

    // When adding a new path segment type, ensure that the returned condition
    // below is still correct.
    static_assert(
        NS_SVG_PATH_SEG_LAST_VALID_TYPE ==
            dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL,
        "Unexpected type");

    return aType & 1;
  }

  static uint32_t RelativeVersionOfType(uint32_t aType) {
    MOZ_ASSERT(IsRelativeOrAbsoluteType(aType),
               "RelativeVersionOfType called with segment type that does not "
               "come in relative and absolute forms");

    // When adding a new path segment type, ensure that the returned condition
    // below is still correct.
    static_assert(
        NS_SVG_PATH_SEG_LAST_VALID_TYPE ==
            dom::SVGPathSeg_Binding::PATHSEG_CURVETO_QUADRATIC_SMOOTH_REL,
        "Unexpected type");

    return aType | 1;
  }

  static uint32_t SameTypeModuloRelativeness(uint32_t aType1, uint32_t aType2) {
    if (!IsRelativeOrAbsoluteType(aType1)) {
      return aType1 == aType2;
    }

    return RelativeVersionOfType(aType1) == RelativeVersionOfType(aType2);
  }

  /**
   * Traverse the given path segment and update the SVGPathTraversalState
   * object.
   */
  static void TraversePathSegment(const float* aData,
                                  SVGPathTraversalState& aState);
};

}  // namespace mozilla

#endif  // DOM_SVG_SVGPATHSEGUTILS_H_