Speeding up QPaint

[georgie]

I think my computer swallowed my last posting of the same info... not sure tho...sorry if this is a double post

Still trying to make my nice array of 100 pretty round buttons even nicer

due to the fact that I often have to update the state of about 25-30 buttons at a time, the repaints that I am calling are kinda slow....

I thought I could maybe speed up the repaints by not calling

QPainter painter (this);

QPainter painter (this);

To copy to clipboard, switch view to plain text mode 

every single repaint, but instead creating the painter on initialisation and having a QPainter* as a member of the RoundButton class - but there are a couple of qns
1. Will this actually make it that much faster?
2. When I try to do this, it says that a painter can only be created for a QWidget (RoundButton is a derivative of QPushButton) during a paint event, so i can't initialize it during construction

anybody tried anything similar? any success? am I barking up the wrong tree completely?

[wysota]

1. Will this actually make it that much faster?

No.

2. When I try to do this, it says that a painter can only be created for a QWidget (RoundButton is a derivative of QPushButton) during a paint event, so i can't initialize it during construction

By default, you can't paint on widgets outside paint events in Qt4. You can pass a flag to a widget that you want to paint on it outside the paint event, but it won't help you much here.

am I barking up the wrong tree completely?

Yes, I think so. You'd better focus on optimising the paint event itself. Use pixmaps, redraw only the part of the widget which needs repainting, use faster routines, etc.

[georgie]

bummer, cause the only reason i ever need to redraw is to change the colour completely, so repainting only a little won't help me much
and it is already a very simple routine which only does the bare minimum so i doubt i can make it much faster



it's just because i always have to do so many at once that it's a prob....oh well....

the only thing i can think of then, is instead of creating a new gradient every time i could draw from one of 3 predefined pixmaps (i want 3 diff colours)....but i don't think this will help either because even when i paint flat colours you can't notice any real speed increase over the gradients....

thanks anyway

[wysota]

But do you always need to redraw the whole widget? Could you show me your paintEvent routine?

[georgie]

for a wonderfully wacky and convoluted reason, the attached pic is what my buttons need to look like...the yellow is the selected, the definition of what a "hex" is follows the yellow one - i.e. if i select a diff button, the diff group of buttons becomes the hex centre so the extra circles get removed from one set of buttons and drawn on a diff set

void RoundButton::paintEvent(QPaintEvent* event)
{
  QRadialGradient grad(15, 15, 35, 0, 0);
  QPainter painter(this);
  grad.setColorAt(0.1, Qt::white);
  if(this->focus)
      grad.setColorAt(0.2, Qt::yellow); //the selected one is yellow
  if(this->arr->getHex()) //if the user has selected "display hex" the buttons get linked into            
                                  //6's by another circle around the one in the centre of the hex
      {
      if(this->hexCentre)
         {
	    grad.setColorAt(0.2, Qt::cyan);
	    QPen pen(Qt::darkRed);
	    painter.setPen(pen);
	    painter.drawEllipse(0.5,0.5,29, 29);
	    pen.setColor(Qt::black);
	    painter.setPen(pen);
	 }
 }
  grad.setColorAt(0.7, Qt::black);
 
  QBrush brush(grad);
  painter.setBrush(brush);
  painter.drawEllipse(8,8,14,14); 
}

void RoundButton::paintEvent(QPaintEvent* event)
{
  QRadialGradient grad(15, 15, 35, 0, 0);
  QPainter painter(this);
  grad.setColorAt(0.1, Qt::white);
  if(this->focus)
      grad.setColorAt(0.2, Qt::yellow); //the selected one is yellow
  if(this->arr->getHex()) //if the user has selected "display hex" the buttons get linked into            
                                  //6's by another circle around the one in the centre of the hex
      {
      if(this->hexCentre)
         {
	    grad.setColorAt(0.2, Qt::cyan);
	    QPen pen(Qt::darkRed);
	    painter.setPen(pen);
	    painter.drawEllipse(0.5,0.5,29, 29);
	    pen.setColor(Qt::black);
	    painter.setPen(pen);
	 }
 }
  grad.setColorAt(0.7, Qt::black);
  
  QBrush brush(grad);
  painter.setBrush(brush);
  painter.drawEllipse(8,8,14,14); 
}

To copy to clipboard, switch view to plain text mode 

thanks for looking at this

[wysota]

Do you need all those buttons as separate buttons? Wouldn't it be easier to have a single widget which handles them all?

I see your paint events shouldn't experience any slowdowns. The reason has to be somewhere else. The only thing you may improve here is not to generate the gradient every repaint -- make it a member of the button and modify it only when it changes.

[georgie]

to a point, i guess it would be better....but there is quite a bit of associated "internal state" info which goes with each button.....which would get mighty confusing with one big widget :S

thanks for your help though

[wysota]

to a point, i guess it would be better....but there is quite a bit of associated "internal state" info which goes with each button.....which would get mighty confusing with one big widget :S

Why? You can keep states of each of the buttons in some data structure.

[georgie]

i never thought about it like that....how would you be able to register a click within a region - like if there was just one big widget but i wanted to click on button number 5, how would i know exactly where the user had clicked? I was using the mousePressEvent of each individual widget....

[georgie]

keeping the gradient as a "has a" member does speed stuff up quite a bit, but the first time i set the colour at 0.2, this cannot be changed in subsequent repaints (i.e. if i deselect something, it remains its selected colour....e.g. if it was the selected one, but then it becomes only the centre of a hex, instead of going from yellow to cyan it stays yellow for the remainder)

there doesn't seem to be an "unsetColorAt()" function, so i think it is necessary to keep initializing a new grad....which is a bummer cause it made it so much better

[wysota]

i never thought about it like that....how would you be able to register a click within a region - like if there was just one big widget but i wanted to click on button number 5, how would i know exactly where the user had clicked? I was using the mousePressEvent of each individual widget....

void MyWidget::mousePressEvent(QMouseEvent *e){
  QPoint clicked = e->pos();
  // now calculate which button was clicked (if any)
  // for example (simplified problem):
  //  X X X X X
  //   X X X X
  //  X X X X X
  //   X X X X 
  // each X is 20x20px
  // row:
  int row = clicked.y()/20;
  // col:
  int col = clicked.x()/20;
  // check if position occupied and ignore otherwise:
  if(row % 2 && !(col%2)) return; // odd numbered row and even numbered column (starting from 0)
  if(!(row%2) && col%2) return; // even numbered row and odd numbered column
  // now it should be easy to map [row x column] to a button, for example:
  QPoint buttoncoords(row/2, col/2);
  emit buttonClicked(buttoncoords);
}

void MyWidget::mousePressEvent(QMouseEvent *e){
  QPoint clicked = e->pos();
  // now calculate which button was clicked (if any)
  // for example (simplified problem):
  //  X X X X X
  //   X X X X
  //  X X X X X
  //   X X X X 
  // each X is 20x20px
  // row:
  int row = clicked.y()/20;
  // col:
  int col = clicked.x()/20;
  // check if position occupied and ignore otherwise:
  if(row % 2 && !(col%2)) return; // odd numbered row and even numbered column (starting from 0)
  if(!(row%2) && col%2) return; // even numbered row and odd numbered column
  // now it should be easy to map [row x column] to a button, for example:
  QPoint buttoncoords(row/2, col/2);
  emit buttonClicked(buttoncoords);
}

To copy to clipboard, switch view to plain text mode 

keeping the gradient as a "has a" member does speed stuff up quite a bit, but the first time i set the colour at 0.2, this cannot be changed in subsequent repaints (i.e. if i deselect something, it remains its selected colour....e.g. if it was the selected one, but then it becomes only the centre of a hex, instead of going from yellow to cyan it stays yellow for the remainder)

there doesn't seem to be an "unsetColorAt()" function, so i think it is necessary to keep initializing a new grad....which is a bummer cause it made it so much better

So create a new one if it changes. Most of the time it won't change.

void MyButton::paintEvent(QPaintEvent *e){
  if(buttonStateChanged){
    grad = QRadialGradient (15, 15, 35, 0, 0);
    grad.setColorAt(0.1, Qt::white);
    grad.setColorAt(0.2, ...);
    grad.setColorAt(..., ...);
  }
  QPainter p(this);
  drawButton(&p);
}

void MyButton::paintEvent(QPaintEvent *e){
  if(buttonStateChanged){
    grad = QRadialGradient (15, 15, 35, 0, 0);
    grad.setColorAt(0.1, Qt::white);
    grad.setColorAt(0.2, ...);
    grad.setColorAt(..., ...);
  }
  QPainter p(this);
  drawButton(&p);
}

To copy to clipboard, switch view to plain text mode 

or even predefine gradients:

class MyButton : public ... {
//...
private:
static QRadialGradient normalGradient;
static QRadialGradient selectedGradient;
static QRadialGradient someotherGradient;
//...
};
//...
QRadialGradient MyButton::normalGradient = QRadialGradient(15, 15, 35, 0, 0);
//...

class MyButton : public ... {
//...
private:
static QRadialGradient normalGradient;
static QRadialGradient selectedGradient;
static QRadialGradient someotherGradient;
//...
};
//...
QRadialGradient MyButton::normalGradient = QRadialGradient(15, 15, 35, 0, 0);
//...

To copy to clipboard, switch view to plain text mode 

[georgie]

i only ever call repaint if it changes, so this will make no difference....
*BUT* I will definitely try your last idea....it sounds like it will do the trick....thankyou for your help