[OpenLayers-Users] Smooth transition between two Image layers

[Jesper Larsen]

Hi Kenneth and others,

Thank you for taking the time to elaborate on Christophers suggestion,
it was really helpful (I am new to OpenLayers so I haven't really got
an overview of the code). It seems to solve the problem. I will modify
my own version of the OpenLayers code as a first step. When I am more
confortable with the code and use larger parts of it I will try to
submit a patch (otherwise I will probably just break something else).

Regarding turning on "Smooth transition": My impression from the
documentation is that there are only two transition options (for
Layers), namely null and resize. Where is the option you mention
described?

Regards,
Jesper

2008/7/15 Kenneth Skovhede, GEOGRAF A/S <ks at geograf.dk>:
> As I understand Christopher's answer, this is not built into OpenLayers.
> So, you must modify the source code yourself to get this behavior.
>
> "Nothing you can do" then translates to, "There is no option you can switch
> on".
>
> You can start up by looking into Layer\Image.js and the function "setUrl"
> which calls Tile\Image.js "draw", which in turn invokses .\Tile.js "draw".
>
> You can see here that it calls "clear", which is implemented in
> Tile\Image.js.
> I suppose you can simply comment out line 188 in Tile\Image.js:
>     clear: function() {
>         if(this.imgDiv) {
>             //this.hide();  --> Commented out
>             if (OpenLayers.Tile.Image.useBlankTile) {
>                 this.imgDiv.src = OpenLayers.Util.getImagesLocation() +
> "blank.gif";
>             }
>         }
>     },
>
> I have not tested it, so i probably has some sideeffects.
> You may also want to turn on Smooth transition, as that prevents the
> original
> image from hiding before the new one is visible.
>
> And it is fairly annoying to maintain a modified version of OpenLayers, so
> if at all possible,
> you should consider adding this as a selectable option, and submitting the
> change as a patch.
>
> Another option is to replace the function at runtime, but that is bound to
> break when
>  OpenLayers is updated.
>
> Regards, Kenneth Skovhede, GEOGRAF A/S
>
>
> Jesper Larsen skrev:
>
> Hi Christopher, realjax and others,
>
> As I understand your answer Christopher there is nothing I can do to
> avoid the blinking. Is that a correct understanding? In case that is
> not how I should understand your answer I have setup a minimal demo of
> the problem on:
>
> http://jlar.webfactional.com/static/
>
> When you press the switch button (with most of the browsers I have
> tested) the OpenLayers map blinks but the ordinary html img attribute
> does not. Any help on this issue is still very welcome.
>
> Regards,
> Jesper
>
>
> 2008/7/11 Christopher Schmidt <crschmidt at metacarta.com>:
>
>
> On Fri, Jul 11, 2008 at 12:37:05AM -0700, realjax wrote:
>
>
> Jesper-5 wrote:
>
>
> Is the solution to this to use Tween to create a smooth transition
> between to Layers? I tried it but I haven't been able to understand
> how to do it. I hope someone can help me out. What I tried is simply:
>
>
>
> OpenLayers.Tween is not likely going to suit your needs.
> I think you need to search for an external solution that has one layer fade
> out while the other fades in. You could (with a bit of hacking)  prolly get
> this working in combination with a lightweight framework like Mootools for
> example.
>
>
> I don't think this will do what he wants. The proble is that OpenLayers
> intentionally hides images before they're loaded -- look at delayDisplay
> in OpenLayers.Util.createImage.
>
> In general, we have put no effort into changing this behavior.
>
> Regards,
> --
> Christopher Schmidt
> MetaCarta
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