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PDF Document Programmatic Zoom

Hi guys

Using VS2017 on Windows 10 Professional with version 16.3460.0.21 of the PDF Controls. In the code below PDFViewerEx is the name of the form and ViewerCtl is a PdfViewer.PdfDocumentView.

I am trying to make the control zoom with the user using the mousewheel and control key and whilst it is working, I have found what I believe to be a bug. Code follows.

The bug I believe is only in the zoom up functionality - the control move up a page on each scroll and I cater for that by adjusting the page back - that of course is an issue. Can you confirm my code is correct and confirm that there is a bug?


.. 
        enum ZoomDirection { None, Up, Down };

        private void PDFViewerEx_KeyDown(object sender, KeyEventArgs e)
        {
            CtrlIsDown = e.Control;

        }
        private void PDFViewerEx_MouseWheel(object sender, MouseEventArgs e)
        {
            //check if control is being held down
            int page = ViewerCtl.CurrentPageIndex;
            Debug.WriteLine("In mousewhereel event - Zoom Up - page " + ViewerCtl.CurrentPageIndex.ToString());
            if (CtrlIsDown)
            {
                //evaluate the delta's sign and call the appropriate zoom command
                int i = Math.Sign(e.Delta);
                if (i < 0)
                {
                    Zoom(ZoomDirection.Down);

                }
                else if (i > 0)
                {
                    Zoom(ZoomDirection.Up);
                    Debug.WriteLine("In mousewhereel event - Zoom Up1 - page " + ViewerCtl.CurrentPageIndex.ToString());
                    if (page > 1)
                        ViewerCtl.GoToPageAtIndex(page + 1);
                    else
                        ViewerCtl.GoToPageAtIndex(page);

                    Debug.WriteLine("In mousewhereel event - Zoom Up2 - page " + ViewerCtl.CurrentPageIndex.ToString());
                }
            }
        }
        void Zoom(ZoomDirection zd)
        {
            int ZoomLevel = ViewerCtl.ZoomPercentage;
            //Debug.WriteLine("In Zoom event " + ZoomLevel.ToString());
            switch (zd)
            {
                case ZoomDirection.Up:
                    ViewerCtl.ZoomTo(ZoomLevel + 2);
                    break;
                case ZoomDirection.Down:
                    ViewerCtl.ZoomTo(ZoomLevel - 2);
                    break;
                case ZoomDirection.None:
                    ViewerCtl.ZoomTo(ZoomLevel);
                    break;

            }
            //Debug.WriteLine("After Zoom event " + ViewerCtl.ZoomPercentage.ToString());
            CtrlIsDown = false;
        }

        private void ViewerCtl_KeyDown(object sender, KeyEventArgs e)
        {
            CtrlIsDown = e.Control;
        }

        private void ViewerCtl_ZoomChanged(object sender, int zoomFactor)
        {
            Debug.WriteLine("In ViewerCtl_ZoomChanged event");
        }


7 Replies

KK Karthik Krishnaraj Syncfusion Team December 24, 2018 07:19 AM

Hi Darrin, 
 
Greetings from Syncfusion, 
 
On analyzing the provided code snippet, we came to know that you are performing zooming operation on Mouse wheel (Ctrl + mouse scroll) and trying to maintain the current page on zooming. But the page index moves up as reported by you. 
 
While performing zooming internally we have updated the page index based on verticalscrolloffset  
​So we suggest you to update the verticalscrolloffset instead of using GoToPageIndes() 
 
We have modified the provided sample to achieve your requirement of maintaining the page index and position, by using the VerticalScrollOffset and HorizontalScrollOffset of the control instead of CurrentPageIndex and GoToPageAtIndex methods. Please find the code snippet below. 
 
Before perform zooming (Take the backup of VerticalScrollOffset and HorizontalScrollOffset with respect to zoom percentage of 100) 
 
 
int backupVerticalOffset = ViewerCtl.VerticalScrollOffset / ViewerCtl.ZoomPercentage;
int backupHorizontalOffset = ViewerCtl.HorizontalScrollOffset / ViewerCtl.ZoomPercentage;
 
 
 
After perform zooming (Apply the backed up VerticalScrollOffset and HorizontalScrollOffset with respect to the current zoom percentage) 
 
 
ViewerCtl.VerticalScrollOffset = backupVerticalOffset * ViewerCtl.ZoomPercentage; 
ViewerCtl.HorizontalScrollOffset = backupHorizontalOffset * ViewerCtl.ZoomPercentage; 
 
 
 
Regards, 
Karthik. 



DE Darrin Edwards December 25, 2018 11:20 PM

Thanks Karthik, when did VerticalScrollOffset come into play ? It seems that the functionality is not available in 16.3*

MTIA

DWE


DE Darrin Edwards December 26, 2018 02:17 AM

Hello -the zoom function is still not working properly - it still scrolls up or down a fraction even in the example provided - I have uploaded a project which we can both work with if thats ok - its a bit easier using this example rather than the example you provided ...

Attachment: Zoom_Issue_20181226170514_ddbd49df.rar


KC Karthikeyan Chandrasekar Syncfusion Team December 31, 2018 07:45 AM

Hi Darrin, 
We are currently working in this feature and it will be available from our upcoming 2019 Vol-1 main release, which is expected to be available in the mid of March. 
Regards, 
Karthikeyan  



DE Darrin Edwards January 7, 2019 06:52 PM

Hi Karthik - I've resolved the scroll issue by the user of ScrollDisplacementValue as follows:

        void Zoom(ZoomDirection zd)
        {
            int backupVerticalOffset = ViewerCtl.VerticalScrollOffset / ViewerCtl.ZoomPercentage;
            int backupHorizontalOffset = ViewerCtl.HorizontalScrollOffset / ViewerCtl.ZoomPercentage;

            int page = ViewerCtl.CurrentPageIndex;
            int ZoomLevel = ViewerCtl.ZoomPercentage;
            //Debug.WriteLine("In Zoom event " + ZoomLevel.ToString());
            switch (zd)
            {
                case ZoomDirection.Up:
                    ViewerCtl.ZoomTo(ZoomLevel + 2);
                    //                    ViewerCtl.VerticalScrollOffset = (backupVerticalOffset) * ZoomLevel +2;// ViewerCtl.ZoomPercentage;
                    ViewerCtl.ScrollDisplacementValue = -10;
                    Debug.WriteLine("In Zoom event Zoom Direction.Up " + ZoomLevel.ToString());
                    break;
                case ZoomDirection.Down:
                    ViewerCtl.ZoomTo(ZoomLevel - 2);
                    ViewerCtl.ScrollDisplacementValue = 0;
                    Debug.WriteLine("In Zoom event Zoom Direction.Down " + ZoomLevel.ToString());
                    break;
                case ZoomDirection.None:
                    ViewerCtl.ZoomTo(ZoomLevel);
                    Debug.WriteLine("In Zoom event ZoomDirection.None " + ZoomLevel.ToString());
                    break;

            }
            ViewerCtl.VerticalScrollOffset = backupVerticalOffset * ViewerCtl.ZoomPercentage ;
            ViewerCtl.HorizontalScrollOffset = backupHorizontalOffset * ViewerCtl.ZoomPercentage;

            //Debug.WriteLine("After Zoom event " + ViewerCtl.ZoomPercentage.ToString());
            ctrlPressed = false;
        }

Sample code attached. Whilst it works for the moment, I'd be grateful if you would confirm once the bug has been ironed out in the next release.

Regards

Darrin

Attachment: Zoom_Issue__2_20190108094554_e8ff4ee2.rar


AK Ayswarya Krishna Kumar Syncfusion Team January 8, 2019 04:14 AM

Hi Darrin,  
  
Thank you for your update. 
  
As mentioned earlier currently we are working on this feature, we will ensure all the zoom operations on mouse functionality. We will update you with the details once the Volume 1 release is rolled out. 
  
Regards,  
Ayswarya 



SS Sathish Sivakumar Syncfusion Team March 14, 2019 02:22 AM

Hi All, 
 
We are glad to inform you that the feature Magnify PDF documents using CTRL key and mouse wheel where the mouse cursor is pointed to. has been included in our Essential Studio 2019 Volume 1 beta release  v17.1.0.32 and is available for download under the following link.  
 
 
Sample link: 
 
 
Regards, 
Sathish 


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