Delay disappearance of loading screen in single player

[Kieran P]

With the new loading screen, people will want to read the new tips.

Fast computers load the map too quickly though, and don't give users a chance to read them fully.

In single player, stop the game from auto-starting, provide a "Start game" button on the loading screen that the user clicks when they are ready to start.

Provide a local.cfg setting which can disable this pausing.

config.loading.wait_for_user = true

Setting to false does the current behavior of starting the game right away when map is loaded.

[Erik Johansson]

This would be a nice thing on slower computers as well, because then you could set the game to load and go do something else while it's loading. Hopefully the loading will never be slow enough to make that "necessary", but if nothing else it can be nice to have the game start when you're prepared for it rather than just "jump into it" at the end of the loading.

[Philip Taylor]

I'm not sure a config setting is worthwhile here. It'd probably be simpler for users if we detect mouse clicks and key presses while the loading process is ongoing, and disable the pause in that case, so they can trivially just click/press immediately after doing "start game" if they want to start as soon as possible.

Part of the loading actually happens when first rendering the world view (since most graphics files are loaded on-demand by the renderer), so if we want to pause on the loading screen then we ought to make it load as much as possible before that point (probably by doing a hidden render of the initial camera position to force it to load what's needed).

[leper]

Duplicate of #2087 which has a patch.