Ideas to optimise QAbstractItemView::dataChanged

[VRonin]

@kshegunov said in Ideas to optimise QAbstractItemView::dataChanged:

Okay, this is my bad then.

I see what you mean. if a view only reimplemented paintEvent it might break due to this change. fair point probably a note for future releses only then

To summarise where we are, the current "idea" of QAbstractItemView::dataChanged is:

void QAbstractItemView::dataChanged(const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles)
{
    Q_UNUSED(roles)
    // Single item changed
    Q_D(QAbstractItemView);
    if (topLeft == bottomRight && topLeft.isValid()) {
        const QEditorInfo &editorInfo = d->editorForIndex(topLeft);
        //we don't update the edit data if it is static
        if (!editorInfo.isStatic && editorInfo.widget) {
            QAbstractItemDelegate *delegate = d->delegateForIndex(topLeft);
            if (delegate) {
                delegate->setEditorData(editorInfo.widget.data(), topLeft);
            }
        }
        if (isVisible() && !d->delayedPendingLayout) {
            // otherwise the items will be update later anyway
            update(topLeft);
        }
    } else {
        d->updateEditorData(topLeft, bottomRight);
        if (isVisible() && !d->delayedPendingLayout)  {
            const QRect viewportRect = d->viewport->rect(); 
            const QModelIndex parent = topLeft.parent();
            const QRect cornerRect = visualRect(topLeft) | visualRect(bottomRight);
            // If dirty is 1/4th or more of the viewport rect, just trigger a full update
            const QRect cornerRectViewPort = cornerRect & viewportRect;
            if(cornerRectViewPort.width() * cornerRectViewPort.height() * 4 > viewportRect.width() * viewportRect.height())  {
                d->viewport->update();
            }
            else  { // Just fall back to iterating over the model indices
                    QRect dirty(cornerRect);
                    const int maxRow = bottomRight.row();
                    for (int i = topLeft.row(); i < maxRow; ++i)  {
                        const int maxColumn = bottomRight.column() - ((i==maxRow-1) ? 1:0);
                        for (int j = topLeft.column()+ ((i==topLeft.row()) ? 1:0); j < maxColumn; ++j)  {
                            dirty |= visualRect(d->model->index(i, j, parent));
                        }
                    }
                    dirty &= viewportRect;
                    if (!dirty.isEmpty())
                        d->viewport->update(dirty);
            }
        }
    }
#ifndef QT_NO_ACCESSIBILITY
    if (QAccessible::isActive()) {
        QAccessibleTableModelChangeEvent accessibleEvent(this, QAccessibleTableModelChangeEvent::DataChanged);
        accessibleEvent.setFirstRow(topLeft.row());
        accessibleEvent.setFirstColumn(topLeft.column());
        accessibleEvent.setLastRow(bottomRight.row());
        accessibleEvent.setLastColumn(bottomRight.column());
        QAccessible::updateAccessibility(&accessibleEvent);
    }
#endif
    d->updateGeometry();
}

EDIT:

Avoid calculating visualRect for the corners twice in the iteration case

[kshegunov]

@Christian-Ehrlicher
Even though it's not strictly the model API we were discussing, have you any thoughts on the proposed snippet? would it be worth changing like this?

[kshegunov]

After some code-mining the above loop should be equivalent to:

for (int i = topLeft.row(); i < maxRow; ++i)  {
    const int maxColumn = bottomRight.column() - ((i==maxRow-1) ? 1:0);
    for (int j = topLeft.column()+ ((i==topLeft.row()) ? 1:0); j < maxColumn; ++j)  {
        d->viewport->update(visualRect(d->model->index(i, j, parent)));
    }
}

The updates are compressed trough QWidgetBackingStore::markDirty. I know the docs mention this but I couldn't find it in QCoreApplication::compressEvent so I went spelunking, albeit rather short lived.