qlayoutengine.cpp

奇趣公司比较新的qt/emd版本

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#include "qlayout.h"
#include "private/qlayoutengine_p.h"

#include "qvector.h"
#include "qwidget.h"

#include <qlist.h>
#include <qalgorithms.h>

#include <qdebug.h>
//#define QLAYOUT_EXTRA_DEBUG

typedef qint64 Fixed;
static inline Fixed toFixed(int i) { return (Fixed)i * 256; }
static inline int fRound(Fixed i) {
    return (i % 256 < 128) ? i / 256 : 1 + i / 256;
}

/*
  This is the main workhorse of the QGridLayout. It portions out
  available space to the chain's children.

  The calculation is done in fixed point: "fixed" variables are
  scaled by a factor of 256.

  If the layout runs "backwards" (i.e. RightToLeft or Up) the layout
  is computed mirror-reversed, and it's the caller's responsibility
  do reverse the values before use.

  chain contains input and output parameters describing the geometry.
  count is the count of items in the chain; pos and space give the
  interval (relative to parentWidget topLeft).
*/
void qGeomCalc(QVector<QLayoutStruct> &chain, int start, int count,
               int pos, int space, int spacer)
{
    int cHint = 0;
    int cMin = 0;
    int cMax = 0;
    int sumStretch = 0;
    int sumSpacing = 0;

    bool wannaGrow = false; // anyone who really wants to grow?
    //    bool canShrink = false; // anyone who could be persuaded to shrink?

    bool allEmptyNonstretch = true;
    int pendingSpacing = -1;
    int spacerCount = 0;
    int i;

    for (i = start; i < start + count; i++) {
        QLayoutStruct *data = &chain[i];

        data->done = false;
        cHint += data->smartSizeHint();
        cMin += data->minimumSize;
        cMax += data->maximumSize;
        sumStretch += data->stretch;
        if (!data->empty) {
            /*
                Using pendingSpacing, we ensure that the spacing for the last
                (non-empty) item is ignored.
            */
            if (pendingSpacing >= 0) {
                sumSpacing += pendingSpacing;
                ++spacerCount;
            }
            pendingSpacing = data->effectiveSpacer(spacer);
        }
        wannaGrow = wannaGrow || data->expansive || data->stretch > 0;
        allEmptyNonstretch = allEmptyNonstretch && !wannaGrow && data->empty;
    }

    int extraspace = 0;

    if (space < cMin + sumSpacing) {
        /*
          Less space than minimumSize; take from the biggest first
        */

        int minSize = cMin + sumSpacing;

        // shrink the spacers proportionally
        if (spacer >= 0) {
            spacer = minSize > 0 ? spacer * space / minSize : 0;
            sumSpacing = spacer * spacerCount;
        }

        QList<int> list;

        for (i = start; i < start + count; i++)
            list << chain.at(i).minimumSize;

        qSort(list);

        int space_left = space - sumSpacing;

        int sum = 0;
        int idx = 0;
        int space_used=0;
        int current = 0;
        while (idx < count && space_used < space_left) {
            current = list.at(idx);
            space_used = sum + current * (count - idx);
            sum += current;
            ++idx;
        }
        --idx;
        int deficit = space_used - space_left;

        int items = count - idx;
        /*
         * If we truncate all items to "current", we would get "deficit" too many pixels. Therefore, we have to remove
         * deficit/items from each item bigger than maxval. The actual value to remove is deficitPerItem + remainder/items
         * "rest" is the accumulated error from using integer arithmetic.
        */
        int deficitPerItem = deficit/items;
        int remainder = deficit % items;
        int maxval = current - deficitPerItem;

        int rest = 0;
        for (i = start; i < start + count; i++) {
            int maxv = maxval;
            rest += remainder;
            if (rest >= items) {
                maxv--;
                rest-=items;
            }
            QLayoutStruct *data = &chain[i];
            data->size = qMin(data->minimumSize, maxv);
            data->done = true;
        }
    } else if (space < cHint + sumSpacing) {
        /*
          Less space than smartSizeHint(), but more than minimumSize.
          Currently take space equally from each, as in Qt 2.x.
          Commented-out lines will give more space to stretchier
          items.
        */
        int n = count;
        int space_left = space - sumSpacing;
        int overdraft = cHint - space_left;

        // first give to the fixed ones:
        for (i = start; i < start + count; i++) {
            QLayoutStruct *data = &chain[i];
            if (!data->done
                 && data->minimumSize >= data->smartSizeHint()) {
                data->size = data->smartSizeHint();
                data->done = true;
                space_left -= data->smartSizeHint();
                // sumStretch -= data->stretch;
                n--;
            }
        }
        bool finished = n == 0;
        while (!finished) {
            finished = true;
            Fixed fp_over = toFixed(overdraft);
            Fixed fp_w = 0;

            for (i = start; i < start+count; i++) {
                QLayoutStruct *data = &chain[i];
                if (data->done)
                    continue;
                // if (sumStretch <= 0)
                fp_w += fp_over / n;
                // else
                //    fp_w += (fp_over * data->stretch) / sumStretch;
                int w = fRound(fp_w);
                data->size = data->smartSizeHint() - w;
                fp_w -= toFixed(w); // give the difference to the next
                if (data->size < data->minimumSize) {
                    data->done = true;
                    data->size = data->minimumSize;
                    finished = false;
                    overdraft -= data->smartSizeHint() - data->minimumSize;
                    // sumStretch -= data->stretch;