LayoutEngine.cc

/*
The MIT License (MIT)
Copyright (c) 2011 Gene Z. Ragan
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

// Self
#include "LayoutEngine.h"

// Qt
#include <QList>
#include <QVector>
#include <QtDebug>

typedef qint64 Fixed64;
static inline Fixed64 toFixed(int i) { return (Fixed64)i * 256; }
static inline int fRound(Fixed64 i) {
    return (i % 256 < 128) ? i / 256 : 1 + i / 256;
}

void qGeomCalc(QVector<LayoutStruct> &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++) {
        LayoutStruct *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;
            }
            LayoutStruct *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++) {
            LayoutStruct *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;
            Fixed64 fp_over = toFixed(overdraft);
            Fixed64 fp_w = 0;

            for (i = start; i < start+count; i++) {
                LayoutStruct *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;
                    n--;
                    break;
                }
            }
        }
    } else { // extra space
        int n = count;
        int space_left = space - sumSpacing;
        // first give to the fixed ones, and handle non-expansiveness
        for (i = start; i < start + count; i++) {
            LayoutStruct *data = &chain[i];
            if (!data->done
                && (data->maximumSize <= data->smartSizeHint()
                    || (wannaGrow && !data->expansive && data->stretch == 0)
                    || (!allEmptyNonstretch && data->empty &&
                        !data->expansive && data->stretch == 0))) {
                data->size = data->smartSizeHint();
                data->done = true;
                space_left -= data->size;
                sumStretch -= data->stretch;
                n--;
            }
        }
        extraspace = space_left;

        /*
          Do a trial distribution and calculate how much it is off.
          If there are more deficit pixels than surplus pixels, give
          the minimum size items what they need, and repeat.
          Otherwise give to the maximum size items, and repeat.

          Paul Olav Tvete has a wonderful mathematical proof of the
          correctness of this principle, but unfortunately this
          comment is too small to contain it.
        */
        int surplus, deficit;
        do {
            surplus = deficit = 0;
            Fixed64 fp_space = toFixed(space_left);
            Fixed64 fp_w = 0;
            for (i = start; i < start + count; i++) {
                LayoutStruct *data = &chain[i];
                if (data->done)
                    continue;
                extraspace = 0;
                if (sumStretch <= 0)
                    fp_w += fp_space / n;
                else
                    fp_w += (fp_space * data->stretch) / sumStretch;
                int w = fRound(fp_w);
                data->size = w;
                fp_w -= toFixed(w); // give the difference to the next
                if (w < data->smartSizeHint()) {
                    deficit +=  data->smartSizeHint() - w;
                } else if (w > data->maximumSize) {
                    surplus += w - data->maximumSize;
                }
            }
            if (deficit > 0 && surplus <= deficit) {
                // give to the ones that have too little
                for (i = start; i < start+count; i++) {
                    LayoutStruct *data = &chain[i];
                    if (!data->done && data->size < data->smartSizeHint()) {
                        data->size = data->smartSizeHint();
                        data->done = true;
                        space_left -= data->smartSizeHint();
                        sumStretch -= data->stretch;
                        n--;
                    }
                }
            }
            if (surplus > 0 && surplus >= deficit) {
                // take from the ones that have too much
                for (i = start; i < start + count; i++) {
                    LayoutStruct *data = &chain[i];
                    if (!data->done && data->size > data->maximumSize) {
                        data->size = data->maximumSize;
                        data->done = true;
                        space_left -= data->maximumSize;
                        sumStretch -= data->stretch;
                        n--;
                    }
                }
            }
        } while (n > 0 && surplus != deficit);
        if (n == 0)
            extraspace = space_left;
    }

    /*
      As a last resort, we distribute the unwanted space equally
      among the spacers (counting the start and end of the chain). We
      could, but don't, attempt a sub-pixel allocation of the extra
      space.
    */
    int extra = extraspace / (spacerCount + 2);
    int p = pos + extra;
    for (i = start; i < start+count; i++) {
        LayoutStruct *data = &chain[i];
        data->position = p;
        p += data->size;
        if (!data->empty)
            p += data->effectiveSpacer(spacer) + extra;
    }

#ifdef QLAYOUT_EXTRA_DEBUG
    qDebug() << "qGeomCalc" << "start" << start <<  "count" << count <<  "pos" << pos
             <<  "space" << space <<  "spacer" << spacer;
    for (i = start; i < start + count; ++i) {
        qDebug() << i << ':' << chain[i].minimumSize << chain[i].smartSizeHint()
                 << chain[i].maximumSize << "stretch" << chain[i].stretch
                 << "empty" << chain[i].empty << "expansive" << chain[i].expansive
                 << "spacing" << chain[i].spacing;
        qDebug() << "result pos" << chain[i].pos << "size" << chain[i].size;
    }
#endif
}