c# - How to make to limit the image dragging area in app? -

now, i'm developing photo application(windows phone 8.1 runtime) got problem did not limit image dragging area while photos zooming.

here below code:

<canvas name="zoomgrid" visibility="collapsed">     <image x:name="zoomimages"            stretch="fill"            width="480"            height="800"            manipulationdelta="img_intro_manipulationdelta"            rendertransformorigin="0.5,0.5"            manipulationmode="all">         <image.rendertransform>             <compositetransform/>         </image.rendertransform>                     </image> </canvas>  double mincale = 0.5; double maxscale = 10.0;  private void image_manipulationdelta(object sender, manipulationdeltaroutedeventargs e) {                image elemt = sender image;     compositetransform transform = elemt.rendertransform compositetransform;      transform.scalex *= e.delta.scale;     transform.scaley *= e.delta.scale;      transform.translatex += e.delta.translation.x;     transform.translatey += e.delta.translation.y;      if (transform.scalex < mincale) transform.scalex = mincale;     if (transform.scaley < mincale) transform.scaley = mincale;     if (transform.scalex > maxscale) transform.scalex = maxscale;     if (transform.scaley > maxscale) transform.scaley = maxscale;      //to limit images dragging did not success.     double scalewidth = zoomimages.actualwidth * ct.scalex;     double scleheight = zoomimages.actualheight * ct.scaley;      double xdiff = math.max(0, (scalewidth - this.content.actualwidth) / 2);     double ydiff = math.max(0, (scleheight - this.content.actualheight) / 2);      if (math.abs(ct.translatex) > xdiff)         ct.translatex = xdiff * math.sign(e.delta.translation.x);     if (math.abs(ct.translatey) > ydiff)         ct.translatey = ydiff * math.sign(e.delta.translation.y);              } 

i've achieved using helper method check whether image within bounds of element.

in case, element you'd want check image, , want check it's within bounds of canvas.

private bool iselementvisible(frameworkelement element, frameworkelement container)     {         if (!element.isvisible)             return false;          rect bounds = element.transformtoancestor(container).transformbounds(new rect(0.0, 0.0, element.actualwidth, element.actualheight));         rect rect = new rect(0.0, 0.0, container.actualwidth, container.actualheight);          if (rect.left > bounds.right || rect.right < bounds.left || rect.bottom < bounds.top || rect.top > bounds.bottom)         {             return false;         }          return true;     } 

in case, i've used matrixtransform instead of compositetransform, method should same.

i create handlers 'manipulationstarting' , 'manipulationcompleted', where:

manipulationstarting:

1. stores current (pre-manipulation) copy of transform.

manipulationcompleted:

1. check see if image out of bounds (using method i've posted).
2. if out of bounds, revert original transform.

this way, if image dragged out of view - user lifts finger, image pop last location.

if you're interested broader context in used code, have wpf behaviour encapsulates functionality. code on codeplex. class may of interest you.

i hope helps :)