How to speed up a transparent QGraphicsTextItem in Opengl?

[wysota]

Your implementation of shape() and boundingRect() is awfully slow. You are creating painter paths all the time. Cache all the data you can (meaning the shape and the bounding rect), this should already give you some speed improvement.

BTW. The background shouldn't influence the contents of the item's cache... I suspect this is caused by an incorrect result of boundingRect() at the time the cache is being enabled.

[JohannesMunk]

Your implementation of shape() and boundingRect() is awfully slow. You are creating painter paths all the time. Cache all the data you can (meaning the shape and the bounding rect), this should already give you some speed improvement.

Yes, I know. But that's definitely not the speed problem. It makes no difference if I have just one TextItem (thus only one transformation, shape, boundingrect calculation) with a lot of text or lots of textitems with just one line of text. Both are equally slow.

BTW. The background shouldn't influence the contents of the item's cache... I suspect this is caused by an incorrect result of boundingRect() at the time the cache is being enabled.

That is definitely the case! The cache is enabled in the constructor. The boundingrect changes all the time. Through the perspective change..

We are on to something here :->

[JohannesMunk]

Mmh.. What can I do about it?

The ProjectedItem changes its projection. And thus its boundingrect.

I don't set the boundingrect of the textitem at all. I just leave it as it is. Because its a childitem of the projecteditem it gets drawn at the right place.

The ProjectedParentItem has no caching activated.

When would be the right time to activate caching?

[JohannesMunk]

Hey Wysota!

I took the time and added the TextItem to the Widget3D Demo.



So whenever you have the time you are welcome to look at the code. If not, it'll stay that slow a little longer :->

Most relevant file is widget3d.h (CGL3dProjectedItem, CGL3dTextItem, ..).

There you can disable the cachemode. And it works just fine.

I think the core problem is: How can I use caching when the transformation and thus the boundingrect changes all the time?

Thx a lot for your help so far!

Johannes

[wysota]

You have to isolate why the background is black. You can see it is not black in my code so there is nothing wrong with the cache in general. As for your bounding rect - see that when your item has no children its bounding rect will be invalid. If you create the cache at that time and not pass the amount of memory you want allocated for the item's cache, it will allocate as much memory as needed to fit your bounding rect. Which in your case is... 0. This is likely to lead to problems although I'd expect everything to be black, not just the background.

I suggest you start from scratch (or with my code) and build upon it until you encounter a situation where cache fails. It might take shorter than wild bug chasing.

[JohannesMunk]

Caching is only enabled for the TextItem! That is a child to a projecteditem, whose shape/boundingrect code I have given you earlier. The caching of the TextItem should not be affected by that, or is it?

The TextItems-Bounding-Rect seems to be fine, as the cache-related black background suggests.

[wysota]

So is everything alright now or not?

[JohannesMunk]

Hi there!

I'm afraid it is not. The solid black background stays in my application. As you suggested, I continued our minimal error example in introducing the 3DTextItem and a dummy ProjectedItem. Sadly, still works.

main.cpp:

#include <QtGui>
#include <QGLWidget>
#include "textitem.h"
 
class CGLScene : public QGraphicsScene
{
protected:
	void drawBackground(QPainter *painter, const QRectF &rect)
	{
		glClearColor(1.0,1.0,0.0,1.0);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	}
};
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  CGLScene scene;
 
  view.setScene(&scene);
  view.setViewport(new QGLWidget);
 
  CGL3dTextItem* item = new CGL3dTextItem("");
  item->setHTML("<font color=#FF0000>FAT TEST </font>");
 
  scene.addItem(item);
 
  QFont f;
  f.setPointSize(36);
  item->setFont(f);
  item->setFlag(QGraphicsItem::ItemIsMovable);
  //item->setCacheMode(QGraphicsItem::ItemCoordinateCache);
 
  QTransform trans;
  trans.rotate(60, Qt::YAxis);
  item->setTransform(trans);
  item->setOpacity(1);
  view.show();
  return app.exec();
}

#include <QtGui>
#include <QGLWidget>
#include "textitem.h"

class CGLScene : public QGraphicsScene
{
protected:
	void drawBackground(QPainter *painter, const QRectF &rect)
	{
		glClearColor(1.0,1.0,0.0,1.0);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	}
};

int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  CGLScene scene;

  view.setScene(&scene);
  view.setViewport(new QGLWidget);

  CGL3dTextItem* item = new CGL3dTextItem("");
  item->setHTML("<font color=#FF0000>FAT TEST </font>");

  scene.addItem(item);

  QFont f;
  f.setPointSize(36);
  item->setFont(f);
  item->setFlag(QGraphicsItem::ItemIsMovable);
  //item->setCacheMode(QGraphicsItem::ItemCoordinateCache);

  QTransform trans;
  trans.rotate(60, Qt::YAxis);
  item->setTransform(trans);
  item->setOpacity(1);
  view.show();
  return app.exec();
}

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textitem.h - a separate header file for moc to start up.

#ifndef TEXTITEM_H
#define TEXTITEM_H
 
#include <QtGui>
#include <QObject>
 
class CGL3dProjectedItem : public QObject, public QGraphicsItem
{	Q_OBJECT
protected:
	virtual QRectF boundingRect() const {return shape().boundingRect();}
	virtual QPainterPath shape() const {QPainterPath p;QPolygonF polygon = mapToScene(this->childrenBoundingRect());p.addPolygon(polygon);return p;}
	virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0) {}
};
 
class CGL3dTextItem : public CGL3dProjectedItem
{	Q_OBJECT
	Q_PROPERTY(QObject* textitem READ getTextItem)
	Q_PROPERTY(QString text READ getText WRITE setText)
	Q_PROPERTY(QString html READ getHTML WRITE setHTML)
	Q_PROPERTY(QFont font READ getFont WRITE setFont)
public:
	CGL3dTextItem(QString text) : CGL3dProjectedItem()
	{
		_textitem = new QGraphicsTextItem(text,this);
		_textitem->setTextInteractionFlags(Qt::TextBrowserInteraction);
		QTextOption textoption(Qt::AlignCenter);
		textoption.setWrapMode(QTextOption::WrapAtWordBoundaryOrAnywhere);
		_textitem->document()->setDefaultTextOption(textoption);
		_textitem->setCacheMode(QGraphicsItem::ItemCoordinateCache);
		//setHandlesChildEvents(true);
	}
	enum { Type = UserType+2};
	int type() const { return Type;}
	QObject* getTextItem() {return _textitem;}
	QString getText() {return _textitem->toPlainText();}
	void setText(QString plaintext) {_textitem->setPlainText(plaintext);TextChanged();}
	QString getHTML() {return _textitem->toHtml();}
	void setHTML(QString htmltext) {_textitem->setHtml(htmltext);TextChanged();}
	QFont getFont() {return _textitem->font();}
	void setFont(QFont f) {_textitem->setFont(f);TextChanged();}
protected:
	void TextChanged()
	{
	//	SetCenterPos(CGL3d(-_textitem->document()->size().width()/2,0,0));
		//qDebug() << "TextItem Center: " << CenterPos().toString();
	}
private:
	QGraphicsTextItem* _textitem;
};
 
#endif // TEXTITEM_H

#ifndef TEXTITEM_H
#define TEXTITEM_H

#include <QtGui>
#include <QObject>

class CGL3dProjectedItem : public QObject, public QGraphicsItem
{	Q_OBJECT
protected:
	virtual QRectF boundingRect() const {return shape().boundingRect();}
	virtual QPainterPath shape() const {QPainterPath p;QPolygonF polygon = mapToScene(this->childrenBoundingRect());p.addPolygon(polygon);return p;}
	virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = 0) {}
};

class CGL3dTextItem : public CGL3dProjectedItem
{	Q_OBJECT
	Q_PROPERTY(QObject* textitem READ getTextItem)
	Q_PROPERTY(QString text READ getText WRITE setText)
	Q_PROPERTY(QString html READ getHTML WRITE setHTML)
	Q_PROPERTY(QFont font READ getFont WRITE setFont)
public:
	CGL3dTextItem(QString text) : CGL3dProjectedItem()
	{
		_textitem = new QGraphicsTextItem(text,this);
		_textitem->setTextInteractionFlags(Qt::TextBrowserInteraction);
		QTextOption textoption(Qt::AlignCenter);
		textoption.setWrapMode(QTextOption::WrapAtWordBoundaryOrAnywhere);
		_textitem->document()->setDefaultTextOption(textoption);
		_textitem->setCacheMode(QGraphicsItem::ItemCoordinateCache);
		//setHandlesChildEvents(true);
	}
	enum { Type = UserType+2};
	int type() const { return Type;}
	QObject* getTextItem() {return _textitem;}
	QString getText() {return _textitem->toPlainText();}
	void setText(QString plaintext) {_textitem->setPlainText(plaintext);TextChanged();}
	QString getHTML() {return _textitem->toHtml();}
	void setHTML(QString htmltext) {_textitem->setHtml(htmltext);TextChanged();}
	QFont getFont() {return _textitem->font();}
	void setFont(QFont f) {_textitem->setFont(f);TextChanged();}
protected:
	void TextChanged()
	{
	//	SetCenterPos(CGL3d(-_textitem->document()->size().width()/2,0,0));
		//qDebug() << "TextItem Center: " << CenterPos().toString();
	}
private:
	QGraphicsTextItem* _textitem;
};

#endif // TEXTITEM_H

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So maybe the problem is hidden in the kind of transformation I am doing. I will investigate.

Thx

Joh