Right Aligning On Zoom - No Horizontal Scrollbar to Horizontal Scrollbar state

[Jacob-Kizzee]

Hello,

I have run across an issue while implementing Diva for a client. As seen in GIF below the renderer right aligns the page when zooming from a "no-horizontal-scrollbar" state to a "horizontal-scrollbar" state.

I have used the basic demo to illustrate the issue.

The expected result on zoom would be to zoom to center. The zoom-in function works properly and zooms on the center of the view window if the "horizontal-scrollbar" already exists.

The issue appears to lie in the handleZoom function of viewer-core.js. When a focalpoint is not provided (zoom button clicked, not a double click) we see:
offset.left = (viewport.width / 2) - (currentRegion.left - viewport.left)

After reviewing the values of viewport and currentRegion I was unable to understand when and where these values are calculated during the zoom process. They appear to jump around severely when moving between "no-horizontal-scrollbar" state to a "horizontal-scrollbar" state.

The revised code below produces a centered view on zoom into a horizontal scrollbar state, but harms the math for the next zoom-in level when the scrollbar exists:
offset.left = (viewport.width > (viewport._innerDimensions.width / 2) ? (viewport._innerDimensions.width / 2) : viewport.width)/2 - (currentRegion.left - viewport.left)

Am I missing a setting for center align on zoom or has anyone else seen this issue?

Your help and consideration are both greatly appreciated.

Thanks

[EricHanLiu]

This issue also exists when double click zooming (so a focalPoint is given, anywhere on the page) from specific zoom levels and page views. Therefore, it seems like the issue shouldn't even be within the focalPoint calculation (where

left: (viewport.width / 2) - (currentRegion.left - viewport.left)

is calculated) since this calculation shouldn't even happen when double click zooming

Using the basic demo:

• In single page view, going from zoomLevel 2.0 and 3.0 will right align the page, whether using the zoom buttons or double click zooming (anywhere on the page)
• In book page view, going from zoomLevel 1.0 and 2.0 will right align the page, using either zoom method as well.

It is likely that these exact zoomLevels are only compatible with my exact viewport size.
eg. the horizontal scrollbar only appears at zoomlevel 3.0 in single page , but could be at 2.0 for another monitor

[EricHanLiu]

The issue seems to be inside the getPositionForZoomLevel(zoomLevel) function (within handleZoom), when calculating the horizontalOffset.

The exact calculation is

var horizontalOffset = (focalPoint.offset.left * zoomRatio) - focalXToCenter;

It seems the issue could lie with the focalXToCenter, or the focalPoint.offset.left variables

Changing this value changes the alignment when zooming between a no-scrollbar to a scrollbar state.

[EricHanLiu]

Overall it seems that once the zoom level crosses the horizontal scrollbar threshold, the image gets scrolled some pixels to the right (~200px), regardless of where the mouse is. If using double click zooming, it'll still nearly centre around the mouse, but it will offset to the right just a tad

[Jacob-Kizzee]

Hello,

Has there been any consideration or movement on this item as part of Release 6.0?

Thanks,
Jacob