qt 4.4 Issue with too many QGraphicsItems

[spawn9997]

Hello all,

Sorry for the long wait but other work calls.

This is one of the model functions I use to create items and populate the scene from. The other (I have 2 models loading for now) they all will most likely look exactly the same.
Main issue is shear size. We load .5 million items in the largest of projects.

void ShotGraphicsLayer::setShotModel(ShotModel * shotModel){
 
    emit this->loadProgress(0);
    layerRect.setSize(QSize(1,1));
    int nlocs = 0, xColumn,yColumn,zColumn, lineCol;
    int swathCol;
    QString swathVal, lineVal;
    float  x_min, x_max,y_min, y_max;
    float  y_value, x_value;
    //float z_value,z_min, z_max;
 
    nlocs = shotModel->rowCount(QModelIndex());
 
    // get column numbers
    xColumn = shotModel->fieldIndex("x");
    yColumn = shotModel->fieldIndex("y");
    zColumn = shotModel->fieldIndex("z");
 
    lineCol = shotModel->fieldIndex("line");
    swathCol = shotModel->fieldIndex("swname");
    // copy data
 
    QModelIndex sgi_ndx, temp_y_ndx,row_ndx, line_ndx, swath_ndx;
 
    int progress;
    for (int ndx=0; ndx < nlocs; ++ndx) {
 
        progress = (ndx*100)/nlocs;
        if(progress%5==0){
            emit loadProgress(progress);
        }
 
        row_ndx = shotModel->index(ndx,0,QModelIndex());
        sgi_ndx = shotModel->index(ndx,xColumn,QModelIndex());
        temp_y_ndx = shotModel->index(ndx,yColumn,QModelIndex());
        line_ndx = shotModel->index(ndx,lineCol,QModelIndex());
        swath_ndx = shotModel->index(ndx,swathCol,QModelIndex());
 
        x_value = shotModel->data(sgi_ndx,Qt::DisplayRole).toDouble();
        y_value = shotModel->data(temp_y_ndx,Qt::DisplayRole).toDouble();
        lineVal = shotModel->data(line_ndx,Qt::DisplayRole).toString();
        swathVal = shotModel->data(swath_ndx,Qt::DisplayRole).toString();
 
        //z_values[ndx] = shotModel->data(sgi_ndx,Qt::DisplayRole).toDouble();
        ShotGraphicsItem * sgi = new ShotGraphicsItem(this);
 
        sgi->setIndex(row_ndx);
        sgi->setPos(x_value,y_value);
 
        ShotGroup temp;
        temp.insert(lineVal,sgi);
 
        lineGroup.insert(lineVal,sgi);
 
        if (swathGroup.contains(swathVal))     // if old group, add new multimap to old one.
            swathGroup[swathVal] += temp;
        else
            swathGroup.insert(swathVal,temp);
 
        this->setNumber(ndx+1);
        sgi->setToolTip(QString("Shot %1").arg(number));
 
        if (ndx == 0) {
            x_max = x_value;
            x_min = x_value;
            y_max = y_value;
            y_min = y_value;
        } else {
            x_min = std::min(x_min,x_value);
            y_min = std::min(y_min,y_value);
            x_max = std::max(x_max,x_value);
            y_max = std::max(y_max,y_value);
        }
        QRectF rect(0,0,25,25);
        sgi->setRect(rect);
        if (ndx == 0)
            layerRect.setRect(rect.x(),rect.y(),rect.width(),rect.height());
 
    }
 
 
    layerRect.setRect(x_min,y_min,fabs(x_max-x_min),fabs(y_max-y_min));
    emit this->loadProgress(100);
}

void ShotGraphicsLayer::setShotModel(ShotModel * shotModel){

    emit this->loadProgress(0);
    layerRect.setSize(QSize(1,1));
    int nlocs = 0, xColumn,yColumn,zColumn, lineCol;
    int swathCol;
    QString swathVal, lineVal;
    float  x_min, x_max,y_min, y_max;
    float  y_value, x_value;
    //float z_value,z_min, z_max;

    nlocs = shotModel->rowCount(QModelIndex());

    // get column numbers
    xColumn = shotModel->fieldIndex("x");
    yColumn = shotModel->fieldIndex("y");
    zColumn = shotModel->fieldIndex("z");

    lineCol = shotModel->fieldIndex("line");
    swathCol = shotModel->fieldIndex("swname");
    // copy data

    QModelIndex sgi_ndx, temp_y_ndx,row_ndx, line_ndx, swath_ndx;

    int progress;
    for (int ndx=0; ndx < nlocs; ++ndx) {

        progress = (ndx*100)/nlocs;
        if(progress%5==0){
            emit loadProgress(progress);
        }

        row_ndx = shotModel->index(ndx,0,QModelIndex());
        sgi_ndx = shotModel->index(ndx,xColumn,QModelIndex());
        temp_y_ndx = shotModel->index(ndx,yColumn,QModelIndex());
        line_ndx = shotModel->index(ndx,lineCol,QModelIndex());
        swath_ndx = shotModel->index(ndx,swathCol,QModelIndex());

        x_value = shotModel->data(sgi_ndx,Qt::DisplayRole).toDouble();
        y_value = shotModel->data(temp_y_ndx,Qt::DisplayRole).toDouble();
        lineVal = shotModel->data(line_ndx,Qt::DisplayRole).toString();
        swathVal = shotModel->data(swath_ndx,Qt::DisplayRole).toString();

        //z_values[ndx] = shotModel->data(sgi_ndx,Qt::DisplayRole).toDouble();
        ShotGraphicsItem * sgi = new ShotGraphicsItem(this);

        sgi->setIndex(row_ndx);
        sgi->setPos(x_value,y_value);

        ShotGroup temp;
        temp.insert(lineVal,sgi);

        lineGroup.insert(lineVal,sgi);

        if (swathGroup.contains(swathVal))     // if old group, add new multimap to old one.
            swathGroup[swathVal] += temp;
        else
            swathGroup.insert(swathVal,temp);

        this->setNumber(ndx+1);
        sgi->setToolTip(QString("Shot %1").arg(number));

        if (ndx == 0) {
            x_max = x_value;
            x_min = x_value;
            y_max = y_value;
            y_min = y_value;
        } else {
            x_min = std::min(x_min,x_value);
            y_min = std::min(y_min,y_value);
            x_max = std::max(x_max,x_value);
            y_max = std::max(y_max,y_value);
        }
        QRectF rect(0,0,25,25);
        sgi->setRect(rect);
        if (ndx == 0)
            layerRect.setRect(rect.x(),rect.y(),rect.width(),rect.height());

    }


    layerRect.setRect(x_min,y_min,fabs(x_max-x_min),fabs(y_max-y_min));
    emit this->loadProgress(100);
}

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Basically it is....
0) for each row in model
1) get data from model
2) create graphicsitem
3) load index (currently the model is not changing)
3.5) add item to group (QMap) for easier access.
4) set position and adjust boundingRect.

- This function is from a QGraphicsItem that acts as the parent for all of these items so I add the items to the scene through this item and this item to the scene through its parent.
So I have... singular item added to scene-> this item has 2 children -> and these two have many child items, each.

Anyway, can anyone see how to load the data from the model quicker or make better use of the model, let me (us) know.


spawn9997
sw developer

[pherthyl]

I would profile which part of that loading function is actually taking the most time..

Nothing obvious jumps out at me.. If you don't need the sorting in your map you can use a QHash, should have much faster insertion times.

[spawn9997]

Sorry for the long get back... the function is just long because of the great number of items. I found that creating QGraphicsItem's takes a good amount of time and accessing the data from the model take time.
We decided to let the load time stand as it is under half a minute for the largest projects including the drawing of the final scene to the QGraphicsView. We did add a progress bar for the user's sake!! Thanks again.

JW
sw developer