Delegate paint optimisation

Here is two delegated QListView of 1000 items,
One is fast, the other is slow.

http://bunjeee.free.fr/slowFast.png

When the area is wider, the painting is *much* slower.

Here is my delegate paint function

Code:

---

void ZeChatRoom_delegate::paint(QPainter *painter, 
								  const QStyleOptionViewItem &option, 
								  const QModelIndex &index) const 
{
   // QItemDelegate::paint(painter, option, index);
 
	ZeChatRoom_data * chatData = index.data().value<ZeChatRoom_data *>();
 
	// Display rects
	QRect pictureRect(option.rect.x() + 2, option.rect.y() + 2, 32, 32);
 
	QRect displayRect = QRect(option.rect.x() + 36, option.rect.y() + 2,
							  option.rect.width() - 38, (option.rect.height() - 4) / 2);
 
	QRect displayRect2 = QRect(option.rect.x() + 36, option.rect.y() + option.rect.height() / 2,
							  option.rect.width() - 38, (option.rect.height() - 4) / 2);
 
	QColor textColor = Qt::black;
	QColor descriptionColor = ZeStyle::get()->getDarkBorderColor();
 
	if (option.state & QStyle::State_MouseOver)
	{
		ZePainterController::get()->DrawHighlight(*painter, option.rect);
 
		textColor = ZeStyle::get()->getHighlightTextColor();
		descriptionColor = ZeStyle::get()->getHighlightTextColor();
 
		ZePainterController::get()->
		DrawBottomLine(*painter, option.rect, QColor(100, 100, 100, 150));
	}
	else
	{
		if (index.row() %2 == 0)
		{
			ZePainterController::get()->
				DrawBack(*painter, option.rect, QColor(ZeStyle::get()->getBorderColor().red(),
							ZeStyle::get()->getBorderColor().green(),
							ZeStyle::get()->getBorderColor().blue(), 50), false);
		}
 
			ZePainterController::get()->
		DrawBottomLine(*painter, option.rect, 
					   /*QColor(100, 100, 100, 150)*/ QColor(ZeStyle::get()->getBorderColor().red(),
							ZeStyle::get()->getBorderColor().green(),
							ZeStyle::get()->getBorderColor().blue(), 200));
	}
 
	ZePainterController::get()->
		DrawPictureRatio(*painter, *chatData->mChatPixmap, pictureRect, 1.0f);
 
	QFont font;
	font.setBold(true);
	ZePainterController::get()->DrawText(*painter, 
										 displayRect, 
										 chatData->mRoomName + " - " + QString::number(chatData->mParticipants),
										 Qt::AlignLeft | Qt::AlignVCenter | Qt::TextSingleLine, 
										 textColor,
										 &font);
 
	ZePainterController::get()->DrawText(*painter, 
										 displayRect2, 
										 chatData->mDescription,
										 Qt::AlignLeft | Qt::AlignVCenter | Qt::TextSingleLine, 
										 descriptionColor);
}

---

Is there a way to optimize the painting ? Especially when you're painting plain grey rectangles at each refresh.

Hard to say without knowing what all those functions of yours do.

This one draws the grey background:

Code:

---

void ZePainterController::DrawBack(QPainter & painter, const QRect &rect, 
								   const QColor & color, const bool border)
{
	QRect rectBase;
 
	if (border)
	{
		QPen pen;
		pen.setBrush(ZeStyle::get()->getBorderColor());
		painter.setPen(pen);
 
		rectBase.setRect(rect.x(), rect.y(), 
						 rect.width() - 1, rect.height() - 1);
	}
	else
	{
		painter.setPen(Qt::NoPen);
 
		rectBase.setRect(rect.x(), rect.y(), 
						 rect.width(), rect.height());
	}
 
	painter.setBrush(QColor(color.red(), color.green(), color.blue(), color.alpha()));
	painter.drawRect(rectBase);
}

---

This one draws the text:

Code:

---

void ZePainterController::DrawText(QPainter & painter, 
								   const QRectF & rect, 
								   const QString & text,
								   int flags,
								   const QColor & color,
								   const QFont * font,
								   const bool elided)
{
	painter.save();
 
	QString finalText;
 
	if (font)
	{
		painter.setFont(*font);
	}
 
	if (elided)
	{
		QFontMetrics fontMetric(painter.font());
		finalText = fontMetric.elidedText(text, 
										  Qt::ElideRight, 
										  rect.width());
	}
	else
	{
		finalText = text;
	}
 
	QPen pen;
 
	pen.setBrush(color);
	painter.setPen(pen);
 
	painter.drawText(rect, flags, finalText);
 
	painter.restore();
}

---

This one draws the picture

Code:

---

void ZePainterController::DrawPictureRatio(QPainter & painter, QPixmap & pixmap, 
										   const QRect &rect, const float opacity)
{
	int gapWidth = 0;
	int gapHeight = 0;
 
	if (rect.width() > pixmap.width())
	{
		gapWidth = (rect.width() - pixmap.width()) / 2;
	}
	if (rect.height() > pixmap.height())
	{
		gapHeight = (rect.height() - pixmap.height()) / 2;
	}
 
	QRect displayRect(rect.x() + gapWidth, rect.y() + gapHeight,
					  pixmap.width(), pixmap.height());
 
	DrawPicture(painter, pixmap, displayRect, opacity);
}

---

...Hope that didn't kill you :).

I don't see any reason why increasing the width should significantly reduce rendering speed. Have you tried using a profiler to find the bottleneck?

Maybe it's my QT 4.4 Release candidate. I'll do some more tests :/

No, there is really nothing that would cause such a slowdown there, regardless of the Qt version used. I really suggest profiling.

Alright,
Transparency seems to be the problem.

I have several QListViews in a list of widget.

The listviews have their back set to transparent :

Code:

---

QPalette palette;
	palette.setColor(QPalette::Base, QColor(0, 0, 0, 0));
	mListView->setPalette(palette);

---

The widget list has a custom paint event, painting a custom color.

Several layers of transparency seems to reduce performances.

Where exactly do you have those layers of transparency?

I had the following paint event in my *Home made* list of widgets:

Code:

---

void ZeBaseListWidget::paintEvent(QPaintEvent * event)
{
	mScrollArea->setBackgroundColor(mListColor);
	QPainter painter(this);
 
	painter.setPen(Qt::NoPen);
	if (mListColor == Qt::white)
	{
		painter.setBrush(ZeStyle::get()->getColorList());
	}
	else
	{
		painter.setBrush(mListColor);
	}
 
	painter.drawRect(rect());
}

---

Now I'm doing like that:

Code:

---

QPalette palette;
	palette.setColor(QPalette::Background, color);
	setPalette(palette);

---

If specify the background palette instead of painting it, performances are better.

On the flipside, I have to notify my widget list everytime the background color changes.

What is mScrollArea? By the way, there are some flags you might use to optimize performance. Caching some things might also speed up things. If you still didn't run your code through a profiler, I really suggest to do that.

mScrollArea was commented.

Yes, I'll do some profiling. I need to work on memory consumption too, since my program is quite heavy.

Do you have a particular tool to suggest ?

Beside this, model view approach works great.


Off topic, but I like your retargetting implementation (QRetargetScale) on your blog.

Thanks for all the help you provided me,
I'll put your name and blog in the "about" of my program :).

Quote:

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Originally Posted by bunjee

Do you have a particular tool to suggest ?

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Depends what OS you are using. I'd suggest gprof or valgrind (cachegrind, to be exact) if they are available for your platform.

Quote:

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Off topic, but I like your retargetting implementation (QRetargetScale) on your blog.

Thanks for all the help you provided me,
I'll put your name and blog in the "about" of my program :).

---

Thx :)