I've god an OpenLayer web with a custom XYZ layer which downloads tiles from the server itself:

OpenLayers.Layer.MOBAC_OSMDROID_ZIP = OpenLayers.Class(
          OpenLayers.Layer.XYZ, {
              name: "tiles base",
              transitionEffect: "resize",
              sphericalMercator: true,
              url: '../map/${z}/${x}/${y}.png',
              [...]
          });

The funny thing here is that I can use MOBAC to download selected parts of OpenStreetMap and serve them from my website. So far, so good.

The problem is: obviously I do not want to download the whole world from OpenStreetMap, but only, for example, zoom levels 0 & 1 for the world, 2-4 for Europe, 5-7 for Spain and so on. Then, when I am zomming in to Spain I get the right tiles. But if I move outside Spain, I just get the damn pink "no-tile" image. I can easily remove such no-image with the .olImageLoadError CSS class... but it still does not show a map.

What I would like is: if there is no tile, use the previous tile, scaled. This way you will probably have an overview of where you are when there are no specific tiles for such level.

I idea? Is something like this included in OpenLayers? Any idea to implemente it myself?

Since the "resize" effect does not remove the old tiles for a while, maybe keeping them "forever" would work...