[BUG] minimap zoom level

[Mariculous]

On stephenson-siemens, everything was all right due to the small map.
On bridgewater, however, the maximum zoom is still quite tiny and the minimum zoom will still show very much black around a tiny map.

I would rather expect a constant size of minimap pixels in specific zoom levels, either constant in on-screen pixles or constant in on-screen percents.

[jamespetts]

This is not a bug - this is how the minimap has always been. That it might benefit from some improvement is not the same as it being an actual bug.

[Vladki]

Could this be related with the minimap crash? https://forum.simutrans.com/index.php/topic,19882.0.html

Open small game, open minimap, zoom in, open big game, open minimap, crash because you tried to zoom in to unsupported level

[Mariculous]

Yes, it seems to be related.

[Ranran(retired)]

I took a little look at this limitation, but I don't know much about it, so I need someone's perspective.
I found a comment in the code as to why zoom in is limited on large maps.

https://github.com/jamespetts/simutrans-extended/blob/f2aab7f6dca1201a3751eb23650f092b061ea6f1/gui/karte.cc#L534

Is it difficult to mitigate zoom-in? (´・ω・｀)

[Mariculous]

I had a look a the code and it's actually correct that your linked line forbids the game to zoom in further, to prevent an overflow in karte_to_screen.

karte_to_screen is quite straight forward: It takes a map koord and multiplies it by zoom_in and divides it by zoom_out. One of these two is always 1.
That will result in an overflow for sure, if koord * zoom_in is greater or equal to 2^15.
Later, that calculated screen koord will be offset according to maps viewport.

I see two possible solutions here:
1. Use an sint32 version of the screen koord.

2. Apply the offset before scaling to screen koord.
Applying an offset to coordinates before passing them karte_to_screen, so the top-left corner of current minimaps viewport is (0,0) will circumvent the overflow entirely.
That, however, requires reorganising the minimap drawing code.