Zoom: Preserve Mouse-on-Land even when zoomed-out; don't screen-center

[SimonN]

Lix 0.10.9

My original report for NeoLemmix on Lemmings Forums

In Lix, when you zoom in or out of the map, the zoom preserves mouse-on-land only when after that zoom, the visible area leaves no dark-blue borders at the sides of the screen. Otherwise, Lix avoids showing void (out-of-bound areas shown using the dark blue border color) by shifting more visible land onto the screen. If all the land is visible, Lix will also center the land on the screen.

Expected instead:

• When the mouse cursor is over a land pixel, zooming should always preverve mouse-on-land, even at the cost of not shifting all the land into view. The canvas should allow some land to remain out of view when there is still void visible.
• When the mouse cursor is over a void pixel (in the dark blue border beside the visible land), zooming should preserve-on-screen the closest land pixel to the mouse instead, i.e., clamp the preservation land coordinates to the inbound land.