Ajax viewer pan/zoom executes two spatial queries on Chrome

[brucedechant]

Using Chrome, the Ajax viewer executes two GETDYNAMICMAPOVERLAY requests for each pan/zoom. This is readily evident using Fiddler. Since two overlay requests are generated, all of the Fdo spatial queries are executed twice for every layer. This reduces MapGuide performance by a factor of two.

[jbirch]

Wow, that sucks. Is this still an issue in 2.1 Bruce?

[brucedechant]

I just tested this against 2.1 and the problem still exists.

[tomfukushima]

Some info from Arthur: In ajaxmappane.templ, when the function RequestMapImage is invoked, the img tag "mapImage" will send out the http request to get the image. When the "mapImage" is loaded, it's image src will be set to "mapImage1" tag. For IE and FF, "mapImage1" will use the cached image, but for Chrome and Safari, a new request will be sent out. Further investigation is needed to make sure it's not the browser's behavior.

[chrisclaydon]

I've attached a patch that does 2 things:

1) It handles the "behind-the-scenes" loading of images the same way for Chrome that it does for Safari, preventing a stale image from flashing up while the new image loads when mouse-wheel zooming.

2) For Chrome and Safari, we now skip the pre-loading of map and selection images into a hidden image. We already have special handling of image loads for Safari, making use of one hidden and one visible image. The images are swapped each time a new image finishes loading. There is no need for an additional hidden image in this setup. This change fixes the problem of issuing two requests for each new map image.

[chrisclaydon]

I forgot to mention that the patch was created against the sandbox/adsk/2.2gp branch

[chrisclaydon]

Submitted to 2.2gp stream:

​http://trac.osgeo.org/mapguide/changeset/4695

and Trunk:

​http://trac.osgeo.org/mapguide/changeset/4696