Dots while freehand drawing on QGraphicsView and Problem while remove items from QGraphicsView.

[raven-worx]

so a possible solution to 2) could be as simple as:
@
WhiteBoardView::WhiteBoardView()
{
mDrawnPathItem = mWhiteBoardScene->addPath(QPainterPath());
mDrawnPathItem->setBrush( QColor(...) );
mDrawnPathItem->setPen(Qt::NoPen);
}

void WhiteBoardView::drawLineTo(const QPointF &previous, const QPointF &current, const QPen& drawPen)
{
QGraphicsLineItem lineHelper;
lineHelper.setLine( QLineF(previous, current) );
lineHelper.setPen(drawPen);

QPainterPath path = mDrawnPathItem->path();
    path.setFillRule(Qt::WindingFill);
    path.addPath( lineHelper.shape() );
path = path.simplified();

mDrawnPathItem->setPath(path);    //mDrawnPathItem is of type QGraphicsPathItem* and was added in the constructor with an empty QPainterPath()

}
@

[Himanshu Rohilla]

Thanks a lot Raven.

It works very fine. But, I have one more problem with this. If i draw a line with a color (for example: Black) , it draws very fine. But, when i start drawing again with different color(for example: Red) , it also changes the color of drawn lines( Black to Red)...

Once again, thanks a lot....

[raven-worx]

yes sure... solution to your problem was to not create multiple line-items but one single item so get rid of the overlapping edges (dots in your case). Thus a change of color affects the whole item.
If you need to draw multi color lines, then you need to create for every color a own path.

[Himanshu Rohilla]

Thanks Raven.. Now, i am using different different path for every color. It works very fine.

But, i could not understand what you want to say about Eraser concept, sorry.. :(

[raven-worx]

when in "eraser-mode" (in the mouse move event) you create a QPainterPath with the radius and the center of the current mouse position. Now just "subtract":http://qt-project.org/doc/qt-4.8/qpainterpath.html#subtracted the eraser painterpath from every item you have in your graphicsview.
Thats it.

[Himanshu Rohilla]

I try this but not working.... :(

the following is my code.

@WhiteBoardView::WhiteBoardView()
{
/* This is for Red Color */
mRedPathItem = mWhiteBoardScene->addPath(QPainterPath());
mRedPathItem->setPen(Qt::NoPen);

 /*  This is for Green Color */
 mGreenPathItem = mWhiteBoardScene->addPath(QPainterPath());
 mGreenPathItem->setPen(Qt::NoPen);
 
 /*  This is for Blue Color */
 mBluePathItem = mWhiteBoardScene->addPath(QPainterPath());
 mBluePathItem->setPen(Qt::NoPen);

 /*  This is for Eraser */
 mEraserPathItem = mWhiteBoardScene->addPath(QPainterPath());
 mEraserPathItem->setPen(Qt::NoPen);

}

/* When in "Eraser Mode(In mouseMoveEvent)", i am calling the following function. */

void WhiteBoardView::eraseLineTo(const QPointF &current)
{
QPainterPath eraserPath = mEraserPathItem->path();

eraserPath.addEllipse(current, 20,20);

QList<QGraphicsItem*> items = this->items();

for(int i=0; i<items.size(); i++)
{
    QPainterPath drawnPath = items[i]->shape();

    drawnPath.subtracted(eraserPath);
}

}@

[raven-worx]

you need to save the changes back to the item, since you only get a copy of the shape from the item. And also you don't need to add an eraser-item to the scene and add a circle to it on every call ;)
@
void WhiteBoardView::eraseLineTo(const QPointF &current)
{
QPainterPath eraserPath;
eraserPath.addEllipse(current, 20,20);

QList<QGraphicsItem*> items = this->items();

for(int i=0; i<items.size(); i++)
{
    QPainterPath drawnPath = items[i]->shape();
    drawnPath.subtracted(eraserPath);
    items[i]->setShape(drawnPath);
}

}
@

[Himanshu Rohilla]

items[i] which is a QGraphicsItem does not have any "setShape" property. I also create a new instance of QGraphicsPathItem and using that i again set the path. But, it also does not work.

@void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

QList<QGraphicsItem*> items = this->items();

for(int i=0; i<items.size(); i++)
{
    QPainterPath drawnPath = items[i]->shape();

    QGraphicsPathItem *pathItem = new QGraphicsPathItem();

    pathItem->setPath(drawnPath.subtracted(eraserPath));
}

}@

[raven-worx]

sorry...the path property is the right one.

In your code you create a new QGraphicsPathItem but never add it to the scene. And even if you would add it to the scene you would leave the old items in there.
Why not holding your own list of the added QGraphicsPathItem objects?
@
void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

    //m_DrawnItems = QList<QGraphicsPathItem*>
    foreach( QGraphicsPathItem* item, m_DrawnItems)
    {
        QPainterPath drawnPath = item->path();
              drawnPath.subtracted(eraserPath)
        item->setPath(drawnPath);
    }
}

@
so every time you add a linepath to the scene you need to also add it to the m_DrawnItems list

[Himanshu Rohilla]

thanks sir....
Now, everything is going fine... :)

thanks a lot....

[Himanshu Rohilla]

Hi Raven,

As u told me about how to do drawing on QGraphicsView and how to remove drawn paths. Now, i am facing a new problem while removing drawn paths.

If i draw large no. of polygons , then the number of paths will increase and the size of list which maintain all paths(m_DrawnItems) is large. In the following code, which is to remove paths from view, For loop is taking a lot of time in case of large number of path.

@ void WhiteBoardView::EraserLineTo(const QPointF &current, double radius)
{
QPainterPath eraserPath = mEraserPathItem->path();
eraserPath.addEllipse(current, 20,20);

    //m_DrawnItems = QList<QGraphicsPathItem*>
    foreach( QGraphicsPathItem* item, m_DrawnItems)
    {
        QPainterPath drawnPath = item->path();
              drawnPath.subtracted(eraserPath)
        item->setPath(drawnPath);
    }
}@

Is there any way which removes the drawn paths fastly ???

[Himanshu Rohilla]

Another problem is that i can't draw free hand drawing on images which are drawn on QGraphicsView .....