Zooming like in googlemaps

[MickeyKnox]

I would like to be able to zoom like in googlemaps, meaning that the mouse
cursor does not only stay at the same screen coordinates while zooming, but
also on the same map coordinates.

The relevant code in the event handling section looks somewhat like this:

Code: [Select]

178         case sf::Event::MouseWheelMoved:
179             {
186                 float zoom = event.mouseWheel.delta > 0 ? 0.5f : 2.f;
187                 sf::Vector2f newpos (window->getSize().x, window->getSize().y);
188                 newpos /= 2.f;
189                 newpos -= sf::Vector2f (sf::Mouse::getPosition(*window).x, sf::Mouse::getPosition(*window).y);
190                 newpos /= zoom;
191                 view.move (-newpos);
192                 view.zoom (zoom);
194                 break;
195             }
I played around with some of the parameters, but i can't get it to zoom towards
the mouse position. Any suggestions?

[eXpl0it3r]

I'm not sure what's wrong in the math, because I didn't try to understand it.
But wouldn't it be easier if you zoomed first and then reset the view?

[Lo-X]

I'm not sure why you divide the pos by the zoom factor

newpos /= zoom;

If I had to implement such a thing, I think I would start moving the view to the cursor coordinates before actually zooming. Anyway, apart from what I said above, I understand what you're doing and can't say anything else without more precision (or some sleep :p)

[MickeyKnox]

Ok, well, i forgot to present the idea of what i'm doing, here it comes:

First, i calculate the vector between the mouse position and the center
of the screen. Then i scale that vector by the zoom to be applied. Lastly,
i move the view with that vector.

newpos *= zoom makes more sense, i guess, but it didn't work either.
Does it make a difference, if i zoom first and move then? Theoretically,
i mean? However, i tried it and i played around a little with subtle changes
in the ordering of things or the multiplication versus differentiation
without finding the desired result.

I think, the idea presentet above is right, but it seems like i'm missing
something or have to work around some quirks or so...

[MickeyKnox]

Well, i figured it out, the following code does the trick:

Code: [Select]

178         case sf::Event::MouseWheelMoved:
179             {
180                 view.zoom (event.mouseWheel.delta > 0 ? 0.5f : 2.f);
181                 zoom_factor = view.getSize ().y / window->getSize ().y;
182
183                 sf::Vector2f newpos (window->getSize().x, window->getSize().y);
184                 newpos /= 2.f;
185                 newpos -= sf::Vector2f (sf::Mouse::getPosition(*window).x, sf::Mouse::getPosition(*window).y);
186                 newpos *= event.mouseWheel.delta > 0 ? zoom_factor : zoom_factor / 2.f;
187                 view.move (event.mouseWheel.delta > 0 ? -newpos : newpos);
188                 break;
189             }
The trick is, the zoom i'm just about to apply is not enough, i have to scale
the vector by the overall zoom of the view.