[Qt-jambi-interest] Polygonzug

[Gunnar Sletta]

Dawid Sip wrote:
> Hi,
> I'm working on an option in my graphics editing application for drawing 
> Polygon around an object in an image. It should work comparably to Path 
> in Gimp except for that I'd like the line between the last added vertex 
> and the one to be placed to be animated (stretched between the pouse 
> pointer and the last added vertex. I cant really find any example in 
> which i could look up howto do this so I'm hoping someone could point me 
> in the right direction. I forgot to mention.

Hi Dawid,

I assume you want to do this on a QGraphicsView, since this is what you 
were using in the previous post. I've attached a small example that 
shows how this can be done.

Basically you maintain two shapes. The first is what you have built so 
far, in my case a plain QPainterPath. The second is a line. The last 
point on the QPainterPath corresponds to the first point in the line and 
when you move the mouse you update the last point in the line, thus 
animating it along the cursor.

If you want to do this on a plain widget it will be almost identical, 
except you need to implement a paintEvent and draw the actual path and line.

> I'm using an small 
> rectangle made in .svg for vertices. This is because i need the polygon 
> to be scalable when i zoom in or out..

QPainter and QGraphicsView are vectorial and will zoom for you. Unless 
you want an especially fancy looking rectangle, just setting a zoom 
factor on the graphics view or painter and drawing the rect will do.

best regards,
Gunnar
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