gfx/public/nsCoord.h
author bzbarsky@mit.edu
Sun, 02 Dec 2007 23:45:06 -0800
changeset 8570 e1f7d1a21089a9b1714a15a135ba04e63fd286f2
parent 6254 7ba94b4dd00c28b7c56754ee6f63274c4726e768
child 9424 f8515770c10d58c35353f0fecc52515eb1af249d
permissions -rw-r--r--
Fix bug 404666 by making spanned colframes be continuations of the col that spans them. r=bernd, sr=roc, a=schrep

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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#ifndef NSCOORD_H
#define NSCOORD_H

#include <math.h>

#include "nsDebug.h"

/*
 * Basic type used for the geometry classes.
 *
 * Normally all coordinates are maintained in the twips coordinate
 * space. A twip is 1/20th of a point, and there are 72 points per
 * inch. However, nscoords do appear in pixel space and other
 * coordinate spaces.
 *
 * Twips are used because they are a device-independent unit of measure. See
 * header file nsUnitConversion.h for many useful macros to convert between
 * different units of measure.
 */

// This controls whether we're using integers or floats for coordinates. We
// want to eventually use floats. If you change this, you need to manually
// change the definition of nscoord in gfx/idl/gfxtypes.idl.
//#define NS_COORD_IS_FLOAT

inline float NS_IEEEPositiveInfinity() {
  union { PRUint32 mPRUint32; float mFloat; } pun;
  pun.mPRUint32 = 0x7F800000;
  return pun.mFloat;
}
inline PRBool NS_IEEEIsNan(float aF) {
  union { PRUint32 mBits; float mFloat; } pun;
  pun.mFloat = aF;
  return (pun.mBits & 0x7F800000) == 0x7F800000 &&
    (pun.mBits & 0x007FFFFF) != 0;
}

#ifdef NS_COORD_IS_FLOAT
typedef float nscoord;
#define nscoord_MAX NS_IEEEPositiveInfinity()
#else
typedef PRInt32 nscoord;
#define nscoord_MAX nscoord(1 << 30)
#endif

#define nscoord_MIN (-nscoord_MAX)

inline void VERIFY_COORD(nscoord aCoord) {
#ifdef NS_COORD_IS_FLOAT
  NS_ASSERTION(floorf(aCoord) == aCoord,
               "Coords cannot have fractions");
#endif
}

inline nscoord NSCoordMultiply(nscoord aCoord, float aVal) {
  VERIFY_COORD(aCoord);
#ifdef NS_COORD_IS_FLOAT
  return floorf(aCoord*aVal);
#else
  return (PRInt32)(aCoord*aVal);
#endif
}

inline nscoord NSCoordMultiply(nscoord aCoord, PRInt32 aVal) {
  VERIFY_COORD(aCoord);
  return aCoord*aVal;
}

inline nscoord NSCoordDivide(nscoord aCoord, float aVal) {
  VERIFY_COORD(aCoord);
#ifdef NS_COORD_IS_FLOAT
  return floorf(aCoord/aVal);
#else
  return (PRInt32)(aCoord/aVal);
#endif
}

inline nscoord NSCoordDivide(nscoord aCoord, PRInt32 aVal) {
  VERIFY_COORD(aCoord);
#ifdef NS_COORD_IS_FLOAT
  return floorf(aCoord/aVal);
#else
  return aCoord/aVal;
#endif
}

/**
 * Returns a + b, capping the sum to nscoord_MAX.
 *
 * This function assumes that neither argument is nscoord_MIN.
 *
 * Note: If/when we start using floats for nscoords, this function won't be as
 * necessary.  Normal float addition correctly handles adding with infinity,
 * assuming we aren't adding nscoord_MIN. (-infinity)
 */
inline nscoord
NSCoordSaturatingAdd(nscoord a, nscoord b)
{
  VERIFY_COORD(a);
  VERIFY_COORD(b);
  NS_ASSERTION(a != nscoord_MIN && b != nscoord_MIN,
               "NSCoordSaturatingAdd got nscoord_MIN as argument");

#ifdef NS_COORD_IS_FLOAT
  // Float math correctly handles a+b, given that neither is -infinity.
  return a + b;
#else
  if (a == nscoord_MAX || b == nscoord_MAX) {
    // infinity + anything = anything + infinity = infinity
    return nscoord_MAX;
  } else {
    // a + b = a + b
    NS_ASSERTION(a < nscoord_MAX && b < nscoord_MAX,
                 "Doing nscoord addition with values > nscoord_MAX");
    NS_ASSERTION((PRInt64)a + (PRInt64)b < (PRInt64)nscoord_MAX,
                 "nscoord addition will reach or pass nscoord_MAX");
    NS_ASSERTION((PRInt64)a + (PRInt64)b > (PRInt64)nscoord_MIN,
                 "nscoord addition will reach or pass nscoord_MIN");

    // Cap the result, just in case we're dealing with numbers near nscoord_MAX
    return PR_MIN(nscoord_MAX, a + b);
  }
#endif
}

/**
 * Returns a - b, gracefully handling cases involving nscoord_MAX.
 * This function assumes that neither argument is nscoord_MIN.
 *
 * The behavior is as follows:
 *
 *  a)  infinity - infinity -> infMinusInfResult
 *  b)  N - infinity        -> 0  (unexpected -- triggers NOTREACHED)
 *  c)  infinity - N        -> infinity
 *  d)  N1 - N2             -> N1 - N2
 *
 * Note: For float nscoords, cases (c) and (d) are handled by normal float
 * math.  We still need to explicitly specify the behavior for cases (a)
 * and (b), though.  (Under normal float math, those cases would return NaN
 * and -infinity, respectively.)
 */
inline nscoord 
NSCoordSaturatingSubtract(nscoord a, nscoord b, 
                          nscoord infMinusInfResult)
{
  VERIFY_COORD(a);
  VERIFY_COORD(b);
  NS_ASSERTION(a != nscoord_MIN && b != nscoord_MIN,
               "NSCoordSaturatingSubtract got nscoord_MIN as argument");

  if (b == nscoord_MAX) {
    if (a == nscoord_MAX) {
      // case (a)
      return infMinusInfResult;
    } else {
      // case (b)
      NS_NOTREACHED("Attempted to subtract [n - nscoord_MAX]");
      return 0;
    }
  } else {
#ifdef NS_COORD_IS_FLOAT
    // case (c) and (d) for floats.  (float math handles both)
    return a - b;
#else
    if (a == nscoord_MAX) {
      // case (c) for integers
      return nscoord_MAX;
    } else {
      // case (d) for integers
      NS_ASSERTION(a < nscoord_MAX && b < nscoord_MAX,
                   "Doing nscoord subtraction with values > nscoord_MAX");
      NS_ASSERTION((PRInt64)a - (PRInt64)b < (PRInt64)nscoord_MAX,
                   "nscoord subtraction will reach or pass nscoord_MAX");
      NS_ASSERTION((PRInt64)a - (PRInt64)b > (PRInt64)nscoord_MIN,
                   "nscoord subtraction will reach or pass nscoord_MIN");

      // Cap the result, in case we're dealing with numbers near nscoord_MAX
      return PR_MIN(nscoord_MAX, a - b);
    }
  }
#endif
}

/**
 * Convert an nscoord to a PRInt32. This *does not* do rounding because
 * coords are never fractional. They can be out of range, so this does
 * clamp out of bounds coord values to PR_INT32_MIN and PR_INT32_MAX.
 */
inline PRInt32 NSCoordToInt(nscoord aCoord) {
  VERIFY_COORD(aCoord);
#ifdef NS_COORD_IS_FLOAT
  NS_ASSERTION(!NS_IEEEIsNan(aCoord), "NaN encountered in int conversion");
  if (aCoord < -2147483648.0f) {
    // -2147483648 is the smallest 32-bit signed integer that can be
    // exactly represented as a float
    return PR_INT32_MIN;
  } else if (aCoord > 2147483520.0f) {
    // 2147483520 is the largest 32-bit signed integer that can be
    // exactly represented as an IEEE float
    return PR_INT32_MAX;
  } else {
    return (PRInt32)aCoord;
  }
#else
  return aCoord;
#endif
}

inline float NSCoordToFloat(nscoord aCoord) {
  VERIFY_COORD(aCoord);
#ifdef NS_COORD_IS_FLOAT
  NS_ASSERTION(!NS_IEEEIsNan(aCoord), "NaN encountered in float conversion");
#endif
  return (float)aCoord;
}

#endif /* NSCOORD_H */