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Thread: Bad performance of QGraphicsScene

  1. 21st November 2008, 22:12 #1
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    Unhappy Bad performance of QGraphicsScene

    Hello,

    I am creating a QGraphicsScene containing only 1416 rects with the following code (see next thread).

    As you can see in traces, I have very bad performances:
    Qt Code: 
    1. ##        >SKGTableWithGraph::redrawGraph
    2. ##          >SKGTableWithGraph::redrawGraph-remove scene
    3. ##          <SKGTableWithGraph::redrawGraph-remove scene TIME=0.287117 ms
    4. ##          >SKGTableWithGraph::redrawGraph-create scene
    5. ##          Scene rect:-10,-354833,394415,394435
    6. ##          Items:24x59=1416
    7. ##          <SKGTableWithGraph::redrawGraph-create scene TIME=57306.6 ms
    8. ##          >SKGTableWithGraph::redrawGraph-add scene to view
    9. ##          <SKGTableWithGraph::redrawGraph-add scene to view TIME=1.1489 ms
    10. ##        <SKGTableWithGraph::redrawGraph TIME=57312.6 ms
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    57s are needed just to build the scene

    In my code, if I comment the addRect methods like this:
    Qt Code: 
    1. if (mode==0) {
    2.                                                 //STACK
    3.                                                 if (val>0) {
    4.                                                         //graphItem=scene->addRect(width*x, -yPlus, width, -val, QPen(), QBrush(color));
    5.                                                         yPlus+=val;
    6.                                                         if (yPlus>ymax) ymax=yPlus;
    7.                                                 } else if (val<0) {
    8.                                                         //graphItem=scene->addRect(width*x, -yMoins, width, -val, QPen(), QBrush(color));
    9.                                                         yMoins+=val;
    10.                                                         if (yMoins<ymin) ymin=yMoins;
    11.                                                 }
    12.                                         } else if (mode==1) {
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    then I have very good performances but my scene is empty (of course).
    Qt Code: 
    1. ##        >SKGTableWithGraph::redrawGraph
    2. ##          >SKGTableWithGraph::redrawGraph-remove scene
    3. ##          <SKGTableWithGraph::redrawGraph-remove scene TIME=0.179953 ms
    4. ##          >SKGTableWithGraph::redrawGraph-create scene
    5. ##          Scene rect:-10,-354833,394415,394435
    6. ##          Items:24x59=1416
    7. ##          <SKGTableWithGraph::redrawGraph-create scene TIME=9.6991 ms
    8. ##          >SKGTableWithGraph::redrawGraph-add scene to view
    9. ##          <SKGTableWithGraph::redrawGraph-add scene to view TIME=0.407059 ms
    10. ##        <SKGTableWithGraph::redrawGraph TIME=13.9419 ms
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    Conclusion: Bad performances are due to addRect method.

    Question: What is the solution to improve performances ?
    I don't understand why "40000 Chips" example is very fast and not my "1416 rects" example !
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  2. 21st November 2008, 22:13 #2
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    Default Re: Bad performance of QGraphicsScene

    Qt Code: 
    1. void SKGTableWithGraph::redrawGraph()
    2. {
    3.         SKGTRACEIN(10, "SKGTableWithGraph::redrawGraph");
    4.         QApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
    5.  
    6.         ui.graphicView->hide();
    7.  
    8.         //Recreate scene
    9.         if (scene) {
    10.                 SKGTRACEIN(10, "SKGTableWithGraph::redrawGraph-remove scene");
    11.                 scene->clear();
    12.                 delete scene;
    13.         }
    14.  
    15.  
    16.         scene=new QGraphicsScene();
    17.         {
    18.                 SKGTRACEIN(10, "SKGTableWithGraph::redrawGraph-create scene");
    19.                 //Get current selection
    20.                 int crow=ui.kTable->currentRow();
    21.                 int ccolumn=ui.kTable->currentColumn();
    22.  
    23.                 int nbRows=ui.kTable->rowCount()-1; //Sum
    24.                 int nbColumns=ui.kTable->columnCount();
    25.                 int sumColumnIndex=nbColumns-1;
    26.                 if (nbColumns>2) {
    27.                         nbColumns=nbColumns-2; //Sum and average
    28.                         --sumColumnIndex;
    29.                 }
    30.                 KLocale* locale=KGlobal::locale();
    31.  
    32.                 int mode=ui.kDisplayMode->currentIndex();
    33.  
    34.                 //Compute y limits
    35.                 double minLimit=0;
    36.                 double maxLimit=0;
    37.                 if (mode==0) {
    38.                         //STACK
    39.                         for (int x=0; x<nbRows; ++x) {
    40.                                 QTableWidgetItem* tableItem=ui.kTable->item(x,sumColumnIndex);
    41.                                 if (tableItem) {
    42.                                         QString valstring=tableItem->text();
    43.                                         double val=locale->readMoney(valstring);
    44.                                         minLimit=qMin(minLimit, val);
    45.                                         maxLimit=qMax(maxLimit, val);
    46.                                 }
    47.                         }
    48.                 } else if (mode==1) {
    49.                         //HISTOGRAM
    50.                         for (int x=0; x<nbRows; ++x) {
    51.                                 for (int y=0; y<nbColumns; ++y) {
    52.                                         QTableWidgetItem* tableItem=ui.kTable->item(x,y);
    53.                                         if (tableItem) {
    54.                                                 QString valstring=tableItem->text();
    55.                                                 double val=locale->readMoney(valstring);
    56.                                                 minLimit=qMin(minLimit, val);
    57.                                                 maxLimit=qMax(maxLimit, val);
    58.                                         }
    59.                                 }
    60.                         }
    61.                 }
    62.  
    63.                 //Compute
    64.                 double width=10;
    65.                 double margin=width;
    66.                 double maxX=0;
    67.                 if (nbRows) {
    68.                         if (mode==0) {
    69.                                 width=(maxLimit-minLimit)/nbRows;
    70.                                 maxX=width*nbRows+margin;
    71.                         } else if (mode==1) {
    72.                                 width=(maxLimit-minLimit)/(nbRows*nbColumns);
    73.                                 maxX=width*(nbColumns-1)*nbRows+margin;
    74.                         }
    75.                 }
    76.                 scene->setSceneRect(-margin, margin-maxLimit, maxX-margin, maxLimit-minLimit+2*margin);
    77.                 scene->setItemIndexMethod(QGraphicsScene::NoIndex);
    78.  
    79.                 SKGTRACE << "Scene rect:" <<scene->sceneRect().x() << "," <<   scene->sceneRect().y()<< "," <<  scene->sceneRect().width()<< "," <<  scene->sceneRect().height() << endl;
    80.                 SKGTRACE << "Items:" <<nbRows << "x" << (nbColumns-1) << "=" << nbRows*(nbColumns-1) << endl;
    81.  
    82.                 //Redraw scene
    83.                 double ymin=0;
    84.                 double ymax=0;
    85.                 double histoPos=0;
    86.                 for (int x=0; x<nbRows; ++x) {
    87.                         QString xname=ui.kTable->item(x, 0)->text();
    88.                         double yPlus=0;
    89.                         double yMoins=0;
    90.                         for (int j=1; j<nbColumns; ++j) {
    91.                                 //Get column name
    92.                                 QString yname=ui.kTable->horizontalHeaderItem(j)->text();
    93.  
    94.                                 //Get cell value
    95.                                 QTableWidgetItem* tableItem=ui.kTable->item(x,j);
    96.                                 if (tableItem) {
    97.                                         QString valstring=tableItem->text();
    98.                                         double val=locale->readMoney(valstring);
    99.  
    100.                                         int color_h=359*x/nbRows;
    101.                                         int color_s=255-155*j/nbColumns;
    102.                                         int color_v=255-155*j/nbColumns;
    103.  
    104.                                         QColor color;
    105.                                         if (x==crow && j==ccolumn) color=QApplication::palette().color(QPalette::Highlight);
    106.                                         else color=QColor::fromHsv(color_h,color_s,color_v);
    107.  
    108.                                         QAbstractGraphicsShapeItem* graphItem=NULL;
    109.                                         if (mode==0) {
    110.                                                 //STACK
    111.                                                 if (val>0) {
    112.                                                         graphItem=scene->addRect(width*x, -yPlus, width, -val, QPen(), QBrush(color));
    113.                                                         yPlus+=val;
    114.                                                         if (yPlus>ymax) ymax=yPlus;
    115.                                                 } else if (val<0) {
    116.                                                         graphItem=scene->addRect(width*x, -yMoins, width, -val, QPen(), QBrush(color));
    117.                                                         yMoins+=val;
    118.                                                         if (yMoins<ymin) ymin=yMoins;
    119.                                                 }
    120.                                         } else if (mode==1) {
    121.                                                 //HISTOGRAM
    122.                                                 graphItem=scene->addRect(width*histoPos, 0, width, -val, QPen(), QBrush(color));
    123.                                                 histoPos++;
    124.                                                 if (val>ymax) ymax=val;
    125.                                                 if (val<ymin) ymin=val;
    126.                                         }
    127.  
    128.                                         if (graphItem) {
    129.                                                 graphItem->setToolTip(xname+'\n'+yname+'\n'+valstring+'\n'+tableItem->toolTip());
    130.                                                 graphItem->setFlags(QGraphicsItem::ItemIsSelectable);
    131.                                                 graphItem->setData(1, x);
    132.                                                 graphItem->setData(2, j);
    133.                                                 graphItem->setData(11, color_h);
    134.                                                 graphItem->setData(12, color_s);
    135.                                                 graphItem->setData(13, color_v);
    136.  
    137.                                                 tableItem->setData(1, (qlonglong)  graphItem);
    138.                                         }
    139.                                 }
    140.                         }
    141.                 }
    142.  
    143.                 //Draw axis
    144.                 if (mode!=2) {
    145.                         QGraphicsLineItem* item=scene->addLine(0, -ymin+margin, 0, -ymax-margin);
    146.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    147.  
    148.                         item=scene->addLine(0, -ymax-margin, margin/2, -ymax-margin/2);
    149.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    150.  
    151.                         item=scene->addLine(0, -ymax-margin, -margin/2, -ymax-margin/2);
    152.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    153.  
    154.                         item=scene->addLine(-margin, 0, maxX, 0);
    155.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    156.  
    157.                         item=scene->addLine(maxX, 0, maxX-margin/2, margin/2);
    158.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    159.  
    160.                         item=scene->addLine(maxX, 0, maxX-margin/2, -margin/2);
    161.                         item->setFlag(QGraphicsItem::ItemIsSelectable, false);
    162.                 }
    163.         }
    164.         {
    165.                 SKGTRACEIN(10, "SKGTableWithGraph::redrawGraph-add scene to view");
    166.                 ui.graphicView->setScene(scene);
    167.                 ui.graphicView->onZoomOriginal();
    168.                 ui.graphicView->show();
    169.                 ui.graphicView->graphicsView()->setOptimizationFlag(QGraphicsView::DontClipPainter, true);
    170.                 ui.graphicView->graphicsView()->setOptimizationFlag(QGraphicsView::DontSavePainterState, true);
    171.                 ui.graphicView->graphicsView()->setOptimizationFlag(QGraphicsView::DontAdjustForAntialiasing, true);
    172.  
    173.                 //Add selection event on scene
    174.                 connect(scene, SIGNAL(selectionChanged()), this, SLOT(onSelectionChangedInGraph()), Qt::QueuedConnection);
    175.         }
    176.         QApplication::restoreOverrideCursor();
    177. }
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  3. 21st November 2008, 22:26 #3
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    Default Re: Bad performance of QGraphicsScene

    First of all add all items to the scene before setting it on the view. Otherwise you get a refresh of the view every time you add an item to the scene.

    Second of all I don't what what your redrawGraph method does, but it recreates all the items instead of using the ones that are already there. Consider a situation where you are building a castle using some building blocks like LEGO. With your current approach if you want to add a new block to the construction, you first dismantle all that you have already constructed, then construct it back and add that new block. Not very efficient, is it? Maybe it's better to simply add that block to the ones that are already there?
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  4. 21st November 2008, 22:52 #4
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    Default Re: Bad performance of QGraphicsScene

    Hi Wysota,

    First of all add all items to the scene before setting it on the view. Otherwise you get a refresh of the view every time you add an item to the scene.
    It's already the case. The scene is created and added to the view.

    Second of all I don't what what your redrawGraph method does, but it recreates all the items instead of using the ones that are already there. Consider a situation where you are building a castle using some building blocks like LEGO. With your current approach if you want to add a new block to the construction, you first dismantle all that you have already constructed, then construct it back and add that new block. Not very efficient, is it? Maybe it's better to simply add that block to the ones that are already there?
    This method creates the view representing the content of a QTableWidget. This method is called when the QTableWidget is populated. So the graph is never updated or modified.

    My problem is that the initial creation is very long.
    I don't understand why "40000 chips" example is able to create 40000 object in less than 1s and why I need 57s to create 1416 rects only.

    What is wrong ?

    PS: Sorry for the previous long message.
    Last edited by jacek; 21st November 2008 at 23:11. Reason: changed [code] to [quote]
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  5. 21st November 2008, 23:59 #5
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    Default Re: Bad performance of QGraphicsScene

    I'd suggest running this code via callgrind to see where the most time is spent. I wouldn't be surprised if it was in the table widget.

    Why is your method called "redraw" if it doesn't redraw?
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  6. 22nd November 2008, 10:05 #6
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    Default Re: Bad performance of QGraphicsScene

    Wysota,

    Performances are very good (13.9419 ms) when the following line is commented:
    Qt Code: 
    1. graphItem=scene->addRect(width*x, -yMoins, width, -val, QPen(), QBrush(color));
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    and very bad (57312.6 ms) when this line is not commented.

    There are nothing concerning QTableView in this line.
    I will try callgrind...

    Thank you for your help.
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  7. 22nd November 2008, 14:01 #7
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    Default Re: Bad performance of QGraphicsScene

    Is there a chance you could provide a minimal compilable example reproducing the problem?
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  8. 23rd November 2008, 21:41 #8
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    Default [RESOLVED] Bad performance of QGraphicsScene

    Hi Wisota,

    I found my error, in fact bad performance was due to the following line:
    Qt Code: 
    1. tableItem->setData(1, (qlonglong)  graphItem);
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    So, you are right, it's due to the QTableView ! Good job !

    I found a solution:
    1-call QTableView::hide at the beginning of SKGTableWithGraph::redrawGraph
    2-call QTableView::shod at the end of SKGTableWithGraph::redrawGraph

    I have now good performances:
    Qt Code: 
    1. ##        >SKGTableWithGraph::redrawGraph
    2. ##          >SKGTableWithGraph::redrawGraph-remove scene
    3. ##          <SKGTableWithGraph::redrawGraph-remove scene TIME=0.206 ms
    4. ##          >SKGTableWithGraph::redrawGraph-create scene
    5. ##          Scene rect:-10,-350985,390567,390587
    6. ##          Items:24x59=1416
    7. ##          <SKGTableWithGraph::redrawGraph-create scene TIME=90.5479 ms
    8. ##          >SKGTableWithGraph::redrawGraph-add scene to view
    9. ##          <SKGTableWithGraph::redrawGraph-add scene to view TIME=454.512 ms
    10. ##        <SKGTableWithGraph::redrawGraph TIME=551.457 ms
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    Thank you again for your help.
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