Multitouch support for Pdf Viewer / Image Editor

[Christine]

Hello,

is there a possibility to support multitouch input on Pdf Viewer and Image Editor?

Moving and tapping is supported. So I can scroll through the pages for example. But I need to use zoom and pinch gesture for zooming in or out to documents / images also.

As we need to zoom just areas (e.g. maps with geo information) and keep the menus on top, the pages are not user-scalable as a whole:
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1,minimum-scale=1, user-scalable=no,text/html,charset=utf-8">

Is there any workaround to catch the event and set the zoom factor?

And is there a possibility to couple the mouse wheel / double click event to the zoom factor?

Thanks,

Christine

[Marc]

So the PDF viewer is totally unusable on mobile devices...

Please fix!

[Marc]

I have been trying for three years to make you understand that the PDF viewer on mobile is almost unusable because you cannot zoom using pinching, the normal way of zooming on mobile devices. It is truly incomprehensible to me that this still hasn’t been addressed, especially since pdf.js, your underlying library, fully supports it.

There has already been a ticket open for a long time, but you simply don’t listen to what I’m saying:
THE PDF VIEWER CANNOT BE USED ON MOBILE!

https://feedback.telerik.com/aspnet-core-ui/1481051-zoom-in-out-file-using-the-build-in-zoom-functionality-of-the-pdfviewer-when-zooming-with-two-fingers

And try zooming on mobile in your own sample:
https://www.telerik.com/blazor-ui/documentation/components/pdfviewer/overview

We produce a newspaper, which means a lot of text on a single page, so our customers must be able to zoom in and out quickly, easily and intuitively. That is exactly why pinching was invented. The dropdown is not convenient when you are in the middle of a page and certainly not the desired or intuitive way of zooming on mobile.

I notice this more often with Telerik. Very simple, practical issues are not being addressed. I call these the “quick wins” that actually keep customers engaged.

It would be great if you could finally fix this and make the Blazor PDF Viewer usable on mobile. In the meantime, we are forced to use another PDF component for mobile. That can’t be the intention, right?

Can you please give this ticket extra priority, considering we have already been waiting five years (!) for this component to become functional?

[Marc]

Technical Explanation for Priority Increase

The current Blazor PDFViewer does not support pinch-to-zoom on mobile devices, even though the underlying rendering engine (pdf.js) natively supports gesture-based zooming. This means that a core browser interaction is being blocked at the component layer rather than by technical limitations of the PDF technology itself.

Key Technical Points

1. pdf.js supports pinch-to-zoom out of the box.
   The Blazor PDFViewer disables or does not expose this functionality. This is an artificial limitation introduced by the Telerik component.

2. touch-action is not the issue.
   Allowing gesture events with CSS does not enable pinch-zoom because the PDFViewer does not implement event listeners for gesturestart, gesturechange, or pointer events required for pinch processing.

3. The PDFViewer only exposes zoom via a toolbar dropdown, which:

   • is not accessible when viewing large documents

   • is not intuitive on mobile

   • is not aligned with standard mobile interaction patterns

4. The absence of mobile zooming makes the component effectively unusable for any document containing:

   • dense text

   • multi-column layouts

   • newspaper or magazine pages

   • technical manuals or PDFs with small fonts

5. This is not a UX improvement request but a core functional requirement for mobile use.
   Every modern mobile PDF viewer (Chrome, Safari, iOS Viewer, Adobe, etc.) supports pinch-to-zoom as a baseline interaction.

Business Impact

We produce and distribute a digital newspaper with thousands of readers who primarily use mobile devices. Without intuitive pinch-zoom, the PDFViewer fails to meet basic usability standards, forcing us to adopt a third-party PDF component despite being long-term Telerik subscribers.

Requested Action

Please enable native pinch-to-zoom support by exposing the existing pdf.js gesture-zoom functionality through the Blazor PDFViewer. This has been requested for several years and is essential for mobile usability.

[Aleksandar]

Hi Christine,

We have a Feature request on improving the experience with zooming for the PDFViewer on mobile devices and I will urge you to vote on it here:

https://feedback.telerik.com/aspnet-core-ui/1481051-zoom-in-out-file-using-the-build-in-zoom-functionality-of-the-pdfviewer-when-zooming-with-two-fingers 

Indeed currently when when you "pinch-zoom" to zoom a PDF file it is zoomed using the browser's zoom functionality, but not the PDFViewer zoom command.

Regards,
Aleksandar
Progress Telerik

[Marc]

Technical Explanation for Priority Increase

The current Blazor PDFViewer does not support pinch-to-zoom on mobile devices, even though the underlying rendering engine (pdf.js) natively supports gesture-based zooming. This means that a core browser interaction is being blocked at the component layer rather than by technical limitations of the PDF technology itself.

Key Technical Points

1. pdf.js supports pinch-to-zoom out of the box.
   The Blazor PDFViewer disables or does not expose this functionality. This is an artificial limitation introduced by the Telerik component.

2. touch-action is not the issue.
   Allowing gesture events with CSS does not enable pinch-zoom because the PDFViewer does not implement event listeners for gesturestart, gesturechange, or pointer events required for pinch processing.

3. The PDFViewer only exposes zoom via a toolbar dropdown, which:

   • is not accessible when viewing large documents

   • is not intuitive on mobile

   • is not aligned with standard mobile interaction patterns

4. The absence of mobile zooming makes the component effectively unusable for any document containing:

   • dense text

   • multi-column layouts

   • newspaper or magazine pages

   • technical manuals or PDFs with small fonts

5. This is not a UX improvement request but a core functional requirement for mobile use.
   Every modern mobile PDF viewer (Chrome, Safari, iOS Viewer, Adobe, etc.) supports pinch-to-zoom as a baseline interaction.

Business Impact

We produce and distribute a digital newspaper with thousands of readers who primarily use mobile devices. Without intuitive pinch-zoom, the PDFViewer fails to meet basic usability standards, forcing us to adopt a third-party PDF component despite being long-term Telerik subscribers.

Requested Action

Please enable native pinch-to-zoom support by exposing the existing pdf.js gesture-zoom functionality through the Blazor PDFViewer. This has been requested for several years and is essential for mobile usability.

[Viktor Tachev]

Hi Marc,

Thank you for the feedback.

The functionality you describe has is logged as a feature request multiple suites - two requests in Blazor and on in UI for ASP.NET Core suites. 

Would you elaborate on what is the technology you are working with so I can reach out to the correct team and ty to raise the priority of the request?

Regards,
Viktor Tachev
Progress Telerik