[OpenLayers-Users] Pink tiles in FireFox doesn't disappear after refresh - a possible solution

[Pietro Ianniello]

WOW!
I was looking on nabble if my post was arrived, made a search and...I have
just found another "solution" like mine!
http://n2.nabble.com/Possible-pink-tile-fix-td1827492.html by Ben Brehmer.
It's interesting, He appends "&retry="+this._attempts;
and by using a temporary var doesn't have to check if it was added or not.

Do have someone else verified it? If yes, will it be included in future OL
versions?

Pietr Ianniello



On Sun, Mar 14, 2010 at 6:16 PM, Pietro Ianniello <
pietro.ianniello at gmail.com> wrote:

> Dear list,
>
> this is second time I make this post: for some reason the first post was
> lost... and it's good because it was buggy!
>
> On to the problem: pink tiles showing up in FireFox.
>
> The pink tiles are generated because of too many connections, so my problem
> it's not that there are pink tiles, the problem it's that when the server is
> reachable again, if I for ex. zoom in and out, they don't desappear as they
> should.
> This is because of aggressive caching on tile to be displayed. If I disable
> caching on server side for tiles, they behave ok... bu I want tiles to be
> able to cache them on clients!
>
> After some days fighting against this problem, enabling caching, disabling
> caching.......... I decided to inspect Openlayers code. It' not all really
> clear, but I realized that the problem *can be* related to "*
> OpenLayers.Util.onImageLoadError*".
> Finally I realized that changing it as reported will fix my problem:
>
> OpenLayers.Util.onImageLoadError = function() {
>     this._attempts = (this._attempts) ? (this._attempts + 1) : 1;
>     if (this._attempts <= OpenLayers.IMAGE_RELOAD_ATTEMPTS) {
>         var urls = this.urls;
>         if (urls && urls instanceof Array && urls.length > 1) {
>             var src = this.src.toString();
>             var current_url, k;
>             for (k = 0; current_url = urls[k]; k++) {
>                 if (src.indexOf(current_url) != -1) {
>                     break;
>                 }
>             }
>             var guess = Math.floor(urls.length * Math.random());
>             var new_url = urls[guess];
>             k = 0;
>             while (new_url == current_url && k++ < 4) {
>                 guess = Math.floor(urls.length * Math.random());
>                 new_url = urls[guess];
>             }
>             this.src = src.replace(current_url, new_url);
>         } else {
>             this.src = this.src;
>         }
>         *OpenLayers.Console.log("attemp n.:",this._attempts);*
>     } else {
>         *OpenLayers.Console.log("error loading", "appending uuu!");**
>         var dummy = "&uuu";
>         if (this.src.match(dummy + "$") != dummy) { //only add if it was
> not added before
>             this.src = this.src + "&uuu";
>         }*
>         this.style.backgroundColor = OpenLayers.Util.onImageLoadErrorColor;
>     }
>     this.style.display = "";
> };
>
> That is: I change the the url of the tile appending some dummy character
> [in this case "uuu", but it can be anything].
> This can be done only if the dummy string was not added before [first post
> bug: I didn't check it]. If you don't check It and the address *this.src*is wrong, you will get OL to continue adding the dummy string going in loop
> and bombardig the server with requests.
> I don't know enough OL to understand why, but that's it.
>
> I would like to have comments from people who knows OL better than me about
> this "solution".
>
> NOTE: it's possible to use the same technique without modifying OL, doing
> something *like* [untested - must be sure about what is '*this*' in the
> context]:
>
> OpenLayers.Util.oldOnImageLoadError = OpenLayers.Util.onImageLoadError;
> OpenLayers.Util.onImageLoadError = function() {
>    this.oldOnImageLoadError();
>    if (this._attempts >= OpenLayers.IMAGE_RELOAD_ATTEMPTS) {
>       //TODO: add dummy
>    }
> }
>
> Pietro Ianniello
>
>
>
>
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