Merge lp:~widelands-dev/widelands/bug-1818494-no-negative-zoom into lp:widelands

[GunChleoc]

Safeguards in draw_terrain to prevent negative zoom.

This is our last remaining known crash, so I'd like this for Build 20. If we can get it in by the weekend, we'll still do the Release Candidate on Monday.

The branch has already been tested and only needs a code review.

[bunnybot (widelandsofficial)]

Continuous integration builds have changed state:

Travis build 4727. State: passed. Details: https://travis-ci.org/widelands/widelands/builds/521578152.
Appveyor build 4512. State: failed. Details: https://ci.appveyor.com/project/widelands-dev/widelands/build/_widelands_dev_widelands_bug_1818494_no_negative_zoom-4512.

[bunnybot (widelandsofficial)]

Continuous integration builds have changed state:

Travis build 4744. State: passed. Details: https://travis-ci.org/widelands/widelands/builds/522405788.
Appveyor build 4529. State: success. Details: https://ci.appveyor.com/project/widelands-dev/widelands/build/_widelands_dev_widelands_bug_1818494_no_negative_zoom-4529.

[GunChleoc (gunchleoc)]

This has been tested, so let's have it before it will delay the release.

@bunnybot merge

=== modified file 'src/wui/mapview.cc'
--- src/wui/mapview.cc	2019-03-31 15:37:35 +0000
+++ src/wui/mapview.cc	2019-04-20 05:46:31 +0000
@@ -352,10 +352,12 @@
 		}
 
 		// Linearly interpolate between the next and the last.
-		const float t = (now - plan[0].t) / static_cast<float>(plan[1].t - plan[0].t);
+		// Using std::max as a workaround for https://bugs.launchpad.net/widelands/+bug/1818494
+		const float t = (std::max(1U, now - plan[0].t)) / static_cast<float>(std::max(1U, plan[1].t - plan[0].t));
 		const View new_view = {
 		   mix(t, plan[0].view.viewpoint, plan[1].view.viewpoint),
-		   mix(t, plan[0].view.zoom, plan[1].view.zoom),
+			// Using math::clamp as a workaround for https://bugs.launchpad.net/widelands/+bug/1818494
+		   math::clamp(mix(t, plan[0].view.zoom, plan[1].view.zoom), 1.f / kMaxZoom, kMaxZoom)
 		};
 		set_view(new_view, Transition::Jump);
 		break;