Fix scaling the legend and scalebar when the resolution is changing (#5029)

[szekerest]

No description provided.

[tbonfort]

The autotests are failing with this patch:

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# renderers => legend_resolution_point_4.png
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compare: image widths or heights differ `../expected/legend_resolution_point_4.png' @ error/compare.c/CompareImageCommand/957.
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# renderers => legend_resolution_point_2.png
######################################
compare: image widths or heights differ `../expected/legend_resolution_point_2.png' @ error/compare.c/CompareImageCommand/957.

it would seem that the images are created with a size different than what was requested.

[szekerest]

@tbonfort I noticed the failure, but I might think that it could be a correct result however. Images at a higher resolution should be proportionally larger in order to keep the same look.

[tbonfort]

Let me disagree. If the user requests a 50x50 image he should get back a 50x50 image. If he wants a similar hi-res image, he should request a 100x100 image and a higher dpi.

[szekerest]

I understand what you mention, but in this case we are talking about the keysize (what is expected), but the autotest check is about the legend image size, which is not the same as the keysize. For example the actual image size for legend_resolution_point_4.png seems to be 199x90 and that won't necessary be the same after the patch, since we also want keysize/keyspacing/hMargin/vMargin to grow proportionally along with the resolution factor.
It is also a theoretical question whether we would want to let the user calculate all these modified parameters externally, or let mapserver to do that so setting the resolution factor should behave something like the symbolscale setting currently. That means the specified keysize would be the same as the pixel size only if the resolution/defresolution =1
But anyway this patch should be refined indeed.

[mapserver-bot]

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