qregion_unix.cpp

奇趣公司比较新的qt/emd版本

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************************************************************************/
/*
 * The functions in this file implement the Region abstraction, similar to one
 * used in the X11 sample server. A Region is simply an area, as the name
 * implies, and is implemented as a "y-x-banded" array of rectangles. To
 * explain: Each Region is made up of a certain number of rectangles sorted
 * by y coordinate first, and then by x coordinate.
 *
 * Furthermore, the rectangles are banded such that every rectangle with a
 * given upper-left y coordinate (y1) will have the same lower-right y
 * coordinate (y2) and vice versa. If a rectangle has scanlines in a band, it
 * will span the entire vertical distance of the band. This means that some
 * areas that could be merged into a taller rectangle will be represented as
 * several shorter rectangles to account for shorter rectangles to its left
 * or right but within its "vertical scope".
 *
 * An added constraint on the rectangles is that they must cover as much
 * horizontal area as possible. E.g. no two rectangles in a band are allowed
 * to touch.
 *
 * Whenever possible, bands will be merged together to cover a greater vertical
 * distance (and thus reduce the number of rectangles). Two bands can be merged
 * only if the bottom of one touches the top of the other and they have
 * rectangles in the same places (of the same width, of course). This maintains
 * the y-x-banding that's so nice to have...
 */
/* $XFree86: xc/lib/X11/Region.c,v 1.1.1.2.2.2 1998/10/04 15:22:50 hohndel Exp $ */

static void UnionRectWithRegion(register const QRect *rect, const QRegionPrivate *source,
                                QRegionPrivate &dest)
{
    if (!rect->width() || !rect->height())
        return;

    QRegionPrivate region(*rect);

    Q_ASSERT(EqualRegion(source, &dest));
    Q_ASSERT(!isEmpty(&region));

    if (dest.numRects == 0)
        dest = region;
    else if (dest.canAppend(&region))
        dest.append(&region);
    else
        UnionRegion(&region, source, dest);
}

/*-
 *-----------------------------------------------------------------------
 * miSetExtents --
 *      Reset the extents and innerRect of a region to what they should be.
 *      Called by miSubtract and miIntersect b/c they can't figure it out
 *      along the way or do so easily, as miUnion can.
 *
 * Results:
 *      None.
 *
 * Side Effects:
 *      The region's 'extents' and 'innerRect' structure is overwritten.
 *
 *-----------------------------------------------------------------------
 */
static void miSetExtents(QRegionPrivate &dest)
{
    register const QRect *pBox,
                         *pBoxEnd;
    register QRect *pExtents;

    dest.innerRect.setCoords(0, 0, -1, -1);
    dest.innerArea = -1;
    if (dest.numRects == 0) {
        dest.extents.setCoords(0, 0, 0, 0);
        return;
    }

    pExtents = &dest.extents;
    pBox = dest.rects.constData();
    pBoxEnd = &pBox[dest.numRects - 1];

    /*
     * Since pBox is the first rectangle in the region, it must have the
     * smallest y1 and since pBoxEnd is the last rectangle in the region,
     * it must have the largest y2, because of banding. Initialize x1 and
     * x2 from  pBox and pBoxEnd, resp., as good things to initialize them
     * to...
     */
    pExtents->setLeft(pBox->left());
    pExtents->setTop(pBox->top());
    pExtents->setRight(pBoxEnd->right());
    pExtents->setBottom(pBoxEnd->bottom());

    Q_ASSERT(pExtents->top() <= pExtents->bottom());
    while (pBox <= pBoxEnd) {
        if (pBox->left() < pExtents->left())
            pExtents->setLeft(pBox->left());
        if (pBox->right() > pExtents->right())
            pExtents->setRight(pBox->right());
        dest.updateInnerRect(*pBox);
        ++pBox;
    }
    Q_ASSERT(pExtents->left() <= pExtents->right());
}

/* TranslateRegion(pRegion, x, y)
   translates in place
   added by raymond
*/

static void OffsetRegion(register QRegionPrivate &region, register int x, register int y)
{
    register int nbox;
    register QRect *pbox;

    pbox = region.rects.data();
    nbox = region.numRects;

    while (nbox--) {
        pbox->translate(x, y);
        ++pbox;
    }
    region.extents.translate(x, y);
    region.innerRect.translate(x, y);
}

/*======================================================================
 *          Region Intersection
 *====================================================================*/
/*-
 *-----------------------------------------------------------------------
 * miIntersectO --
 *      Handle an overlapping band for miIntersect.
 *
 * Results:
 *      None.
 *
 * Side Effects:
 *      Rectangles may be added to the region.
 *
 *-----------------------------------------------------------------------
 */
static void miIntersectO(register QRegionPrivate &dest, register const QRect *r1, const QRect *r1End,
                         register const QRect *r2, const QRect *r2End, int y1, int y2)
{
    register int x1;
    register int x2;
    register QRect *pNextRect;

    pNextRect = dest.rects.data() + dest.numRects;

    while (r1 != r1End && r2 != r2End) {
        x1 = qMax(r1->left(), r2->left());
        x2 = qMin(r1->right(), r2->right());

        /*
         * If there's any overlap between the two rectangles, add that
         * overlap to the new region.
         * There's no need to check for subsumption because the only way
         * such a need could arise is if some region has two rectangles
         * right next to each other. Since that should never happen...
         */
        if (x1 <= x2) {
            Q_ASSERT(y1 <= y2);
            MEMCHECK(dest, pNextRect, dest.rects)
            pNextRect->setCoords(x1, y1, x2, y2);
            ++dest.numRects;
            ++pNextRect;
        }

        /*
         * Need to advance the pointers. Shift the one that extends
         * to the right the least, since the other still has a chance to
         * overlap with that region's next rectangle, if you see what I mean.
         */
        if (r1->right() < r2->right()) {
            ++r1;
        } else if (r2->right() < r1->right()) {
            ++r2;
        } else {
            ++r1;
            ++r2;
        }
    }
}

/*======================================================================
 *          Generic Region Operator
 *====================================================================*/

/*-
 *-----------------------------------------------------------------------
 * miCoalesce --
 *      Attempt to merge the boxes in the current band with those in the
 *      previous one. Used only by miRegionOp.
 *
 * Results:
 *      The new index for the previous band.
 *
 * Side Effects:
 *      If coalescing takes place:
 *          - rectangles in the previous band will have their y2 fields
 *            altered.
 *          - dest.numRects will be decreased.
 *
 *-----------------------------------------------------------------------
 */
static int miCoalesce(register QRegionPrivate &dest, int prevStart, int curStart)
{
    register QRect *pPrevBox;   /* Current box in previous band */
    register QRect *pCurBox;    /* Current box in current band */
    register QRect *pRegEnd;    /* End of region */
    int curNumRects;    /* Number of rectangles in current band */
    int prevNumRects;   /* Number of rectangles in previous band */
    int bandY1;         /* Y1 coordinate for current band */
    QRect *rData = dest.rects.data();

    pRegEnd = rData + dest.numRects;

    pPrevBox = rData + prevStart;
    prevNumRects = curStart - prevStart;

    /*
     * Figure out how many rectangles are in the current band. Have to do
     * this because multiple bands could have been added in miRegionOp
     * at the end when one region has been exhausted.
     */
    pCurBox = rData + curStart;
    bandY1 = pCurBox->top();
    for (curNumRects = 0; pCurBox != pRegEnd && pCurBox->top() == bandY1; ++curNumRects) {
        ++pCurBox;
    }

    if (pCurBox != pRegEnd) {
        /*
         * If more than one band was added, we have to find the start
         * of the last band added so the next coalescing job can start
         * at the right place... (given when multiple bands are added,
         * this may be pointless -- see above).
         */
        --pRegEnd;
        while ((pRegEnd - 1)->top() == pRegEnd->top())
            --pRegEnd;
        curStart = pRegEnd - rData;
        pRegEnd = rData + dest.numRects;
    }

    if (curNumRects == prevNumRects && curNumRects != 0) {
        pCurBox -= curNumRects;
        /*
         * The bands may only be coalesced if the bottom of the previous
         * matches the top scanline of the current.
         */
        if (pPrevBox->bottom() == pCurBox->top() - 1) {
            /*
             * Make sure the bands have boxes in the same places. This
             * assumes that boxes have been added in such a way that they
             * cover the most area possible. I.e. two boxes in a band must
             * have some horizontal space between them.
             */
            do {
                if (pPrevBox->left() != pCurBox->left() || pPrevBox->right() != pCurBox->right()) {
                     // The bands don't line up so they can't be coalesced.
                    return curStart;
                }
                ++pPrevBox;
                ++pCurBox;
                --prevNumRects;
            } while (prevNumRects != 0);

            dest.numRects -= curNumRects;
            pCurBox -= curNumRects;
            pPrevBox -= curNumRects;

            /*
             * The bands may be merged, so set the bottom y of each box
             * in the previous band to that of the corresponding box in
             * the current band.
             */
            do {
                pPrevBox->setBottom(pCurBox->bottom());
                dest.updateInnerRect(*pPrevBox);
                ++pPrevBox;
                ++pCurBox;
                curNumRects -= 1;
            } while (curNumRects != 0);

            /*
             * If only one band was added to the region, we have to backup
             * curStart to the start of the previous band.
             *
             * If more than one band was added to the region, copy the
             * other bands down. The assumption here is that the other bands
             * came from the same region as the current one and no further
             * coalescing can be done on them since it's all been done
             * already... curStart is already in the right place.
             */
            if (pCurBox == pRegEnd) {
                curStart = prevStart;
            } else {
                do {
                    *pPrevBox++ = *pCurBox++;
                    dest.updateInnerRect(*pPrevBox);
                } while (pCurBox != pRegEnd);
            }
        }
    }
    return curStart;
}

/*-
 *-----------------------------------------------------------------------
 * miRegionOp --
 *      Apply an operation to two regions. Called by miUnion, miInverse,
 *      miSubtract, miIntersect...
 *
 * Results:
 *      None.
 *
 * Side Effects:
 *      The new region is overwritten.
 *
 * Notes:
 *      The idea behind this function is to view the two regions as sets.
 *      Together they cover a rectangle of area that this function divides
 *      into horizontal bands where points are covered only by one region
 *      or by both. For the first case, the nonOverlapFunc is called with
 *      each the band and the band's upper and lower extents. For the
 *      second, the overlapFunc is called to process the entire band. It
 *      is responsible for clipping the rectangles in the band, though
 *      this function provides the boundaries.
 *      At the end of each band, the new region is coalesced, if possible,
 *      to reduce the number of rectangles in the region.
 *
 *-----------------------------------------------------------------------
 */
static void miRegionOp(register QRegionPrivate &dest, const QRegionPrivate *reg1, const QRegionPrivate *reg2,
                       OverlapFunc overlapFunc, NonOverlapFunc nonOverlap1Func,
                       NonOverlapFunc nonOverlap2Func)
{
    register const QRect *r1;         // Pointer into first region
    register const QRect *r2;         // Pointer into 2d region
    const QRect *r1End;               // End of 1st region
    const QRect *r2End;               // End of 2d region
    register int ybot;          // Bottom of intersection
    register int ytop;          // Top of intersection
    int prevBand;               // Index of start of previous band in dest
    int curBand;                // Index of start of current band in dest
    register const QRect *r1BandEnd;  // End of current band in r1
    register const QRect *r2BandEnd;  // End of current band in r2