c# - Use TrackBar to Zoom In/out of Picturebox Proportionately -

i'm using winforms. in form have picturebox want zoom in , out using track bar. picturebox set zoom-mode. want image , picturebox proportion height/width when drag bar. how can accomplish this?

    private void open_btn_click(object sender, eventargs e)     {         openfiledialog openfiledialog1 = new openfiledialog();          if(openfiledialog1.showdialog() == dialogresult.ok)         {             image bmp;             bmp = new bitmap(openfiledialog1.filename);             if (bmp == null)             {                 messagebox.show("loading image failed", "error", messageboxbuttons.yesno, messageboxicon.warning);              }             else             {                 picturebox1.image = bmp;                 openfiledialog1.dispose();             }          }      }      private void zoomslider_scroll(object sender, eventargs e)     {         if(trackbar1.value == 1)         {             picturebox1.height += 50;             picturebox1.width +=  50;          }          if(trackbar1.value == 2)         {             picturebox1.height += 100;             picturebox1.width += 100;         }          if(trackbar1.value == 3)         {             picturebox1.height += 200;             picturebox1.width += 200;          }      //this not had in mind...     } 

when form created have save size

form1 : form {    private size _pictoriginalsize;    form1()    {        initialisecomponent();        _pictoriginalsize = picturebox1.size;        zoomslider.minimum = 0;        zoomsldier.maximum = 1000;        ...    } 

now know it's unzoomed size was.

next need need convert value of slider into scale factor.

private void zoomslider_scroll(object sender, eventargs e) {     const double maxscale = 5.0; // scale factor when @ it's max      double scale = math.pow(maxscale, trackbar1.value / trackbar1.maximum);      size newsize = new size((int) (_pictorignalsize.width * scale),                    (int) (_pictorignalsize.height * scale));      picturebox.size = newsize; } 

i using math.pow function convert scale 1 5 on exponential scale - may want use different technique consider

• having slider have values 1 5 , value becomes scale: scale = zoomslider.value - gives resoultion of 1.
• having slider have values 1 5000 , double division double scale = zoomslider.value / 1000.0; gives 1000 different resolutions.

nb: using 5 example - can use value max scale factor.