how to get color at coordinate when i press mouse on canvasview or widget?

[kstking]

I want to know colors at my coordinates when i press mouse on canvasview or widget. how can i do?
i don't know all function to do that. Would you please give me some examples?

[kernel_panic]

you could grab you widget and convert the pixmap into QImage. then you get the pixel under the mouse and get the color of the pixel. i don't know if it works, you have to try.

[wysota]

I want to know colors at my coordinates when i press mouse on canvasview or widget. how can i do?
i don't know all function to do that. Would you please give me some examples?

We tend not to do things this way. What exactly are you trying to achieve? If you use a canvas, you can access a pointer to the item under cursor and then you can often know the colour right away based on the item properties or you can implement your items in a smart way so that it can tell you what colour it has at a specified coordinate.

[sincnarf]

I am currently trying to implement the same thing only on a QGraphicsView. I have a question though, when you click on an item in the graphics view, what coordinates do you get? the coordinates of the image or the graphicsview's scene? i don't get it

[marcel]

Depends how you access the coordinates, but mostly you will get scene coordinates.

[jpn]

A QGraphicsItem receives a QGraphicsSceneMouseEvent which has methods to get the position in any coordinates you want.

QGraphicsSceneMouseEvent::pos():

Returns the mouse cursor position in item coordinates.

QGraphicsSceneMouseEvent::scenePos():

Returns the mouse cursor position in scene coordinates.

QGraphicsSceneMouseEvent::screenPos():

Returns the mouse cursor position in screen coordinates.

The Graphics View Coordinate System docs explain the coordinate system in detailed level.

[kstking]

this is my code:

void FigureEditor::contentsMousePressEvent(QMouseEvent* e)
{
       QPoint p = inverseWorldMatrix().mp(e->pos());
	QPoint tmpPointEdit = e->pos();
        QCanvasItemList l=canvas()->collisions(p);
	QCanvasItemList::Iterator it = l.begin();
        ImageItem *item;
        for (it; it!=l.end(); ++it) {
            if ( (*it)->rtti() == imageRTTI ) {
                item = (ImageItem*)(*it);
                if ( !item->hit( p ) )
                    continue;
            }
 
            tmpPointEdit = p;  
            moving = *it;
            moving_start = p;
            break;
        }
		int ix = tmpPointEdit.x();
		int iy = tmpPointEdit.y();
		QImage *img = (QImage*)(*it);
 		QRgb newPixel = img -> pixel( ix, iy );
}

void FigureEditor::contentsMousePressEvent(QMouseEvent* e)
{
       QPoint p = inverseWorldMatrix().mp(e->pos());
	QPoint tmpPointEdit = e->pos();
        QCanvasItemList l=canvas()->collisions(p);
	QCanvasItemList::Iterator it = l.begin();
        ImageItem *item;
        for (it; it!=l.end(); ++it) {
            if ( (*it)->rtti() == imageRTTI ) {
                item = (ImageItem*)(*it);
                if ( !item->hit( p ) )
                    continue;
            }

            tmpPointEdit = p;  
            moving = *it;
            moving_start = p;
            break;
        }
		int ix = tmpPointEdit.x();
		int iy = tmpPointEdit.y();
		QImage *img = (QImage*)(*it);
 		QRgb newPixel = img -> pixel( ix, iy );
}

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this code is one part of example: http://doc.trolltech.com/3.3/canvas-example.html
i have edited code in pressmouse method .
RUN:
+ First: i draw Rect with Red color on canvas. and use canvasview to show it.
+Second: i click on Rect. I want to get color at position when i press mouse. And save it into newPixel variable.
--> i wrong?

[wysota]

But could you answer the question why you want to know the colour of the pixel under cursor?