[MapServer-dev] SCALEBAR "TRANSPARENT" option was supposed to have been removed on 8.0?

Seth G sethg at geographika.co.uk
Sun Oct 22 01:50:22 PDT 2023

Hi Mateus,

You are correct - there is an issue with the documentation. Originally SCALEBAR TRANSPARENT was marked for removal in the RFC as it had been marked as deprecated since MapServer 4.6. However when testing I ran into the same issue as you, so the TRANSPARENT keyword was reinstated. This is the same with LEGEND TRANSPARENT. See discussion at https://github.com/MapServer/MapServer/pull/6342

I've created a pull request for the docs at https://github.com/MapServer/MapServer-documentation/pull/860

Thanks for reporting,


web:https://geographika.net & https://mapserverstudio.net
twitter: @geographika

On Sat, Oct 21, 2023, at 10:42 PM, Mateus Medeiros via MapServer-dev wrote:
> Hello!
> I've been configuring a bunch of Mapserver 8.0 mapfiles for a WMS server that was served with GeoServer before. I had almost equivalent configurations but for the past two days struggled quite a bit to find a way to have an embedded scalebar box in the corner of the output of a GetMap request.
> Generating the scale itself on top was super easy, but it was always floating on top of the layers, making it quite hard to read in some cases.
> The OUTPUTFORMAT was configured to be a PNG with IMAGEMODE set to RGBA and TRANSPARENT set to ON. This is because I have a raster layer and a bunch of vector layers on top of it, but either of them can contain some holes and the vector styles are mostly outline colors, so I need the GetMap to output an image that can potentially have transparent areas.
> I saw a TRANSPARENT option in the SCALEBAR section in the docs that said "Should the background color for the scalebar be transparent." which sounds like just what I needed, but it said "Removed in version 8.0." and "This flag is now deprecated in favor of declaring transparency within OUTPUTFORMAT declarations. Default is off.". Unfortunately, setting transparency to OFF within the OUTPUTFORMAT declaration didn't work because then the resulting PNG had no transparency at all, including in the layers.
> I tried a bunch of different things with IMAGECOLOR and BACKGROUNDCOLOR, including setting different "alpha" values in the colors ("#FFFFFFDD"), but it seemed to make no difference. I was already accepting that I would have to render the box and then the label as separate repeated layers or maybe overlay that from outside Mapserver, but decided to take a look at the source code (which was surprisingly easy thankfully because the codebase is quite well-organized for a project this size made mostly in C) to see why IMAGECOLOR was not working the way I expected and/or if I could find anything useful in there about how to achieve what I wanted now that the TRANSPARENT option was removed.
> Then I found the function `msDrawScalebar` in the file `src/mapscale.c`, and in there I realized that the TRANSPARENT option seemed to still be accounted (https://github.com/MapServer/MapServer/blob/24d36f842c243f96eba88ff896db1bf34d8a687a/src/mapscale.c#L240-L248). To my surprise, after simply setting "TRANSPARENT" to "OFF" in my SCALEBAR section, lo and behold, it worked flawlessly (I could even control the opacity by including a color with the alpha part as IMAGECOLOR).
> So I went to the documentation repo and tried to find when the "Removed in 8.0" part was added and found the original change referencing RFC #133 (https://mapserver.org/development/rfc/ms-rfc-133.html). It seems the RFC explicitly lists the TRANSPARENT option of SCALEBAR as one that needed to be removed.
> For me it seemed like an error in the documentation, as I couldn't easily find a way to add a non-transparent background box on my SCALEBAR only and therefore it made more sense to me that the setting still existed instead of being removed or deprecated. Unfortunately I ended up using all the time I had to spare trying to identify if the intention was to keep the TRANSPARENT option and adding the removal comment was a mistake or if the comment was ok and the option should have been removed, but couldn't reach a conclusion.
> So I think there's either a bug in the documentation or a bug in Mapserver itself. If indeed the TRANSPARENT option inside the SCALEBAR section was supposed to be removed, then how would I go about achieving this non-transparent scalebar box within a transparent output in a GetMap WMS request? And if it's just the documentation that is wrong, should I just open a PR correcting that in the Mapserver docs repo? Or are there other steps I should take before as part of the process of contributing a change like that in the docs?
> Thanks for the help!
> Mateus Medeiros
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