From 762fcfc2dbdc5867646c9ed13a262bb18ebb9a9b Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Mon, 12 Mar 2018 03:23:04 +0900
Subject: [PATCH] examples/airship: Bug fix: stop if z value equals to or is
 less than 0

---
 examples/airship/main.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/examples/airship/main.go b/examples/airship/main.go
index 5f0e37f74..65c495c50 100644
--- a/examples/airship/main.go
+++ b/examples/airship/main.go
@@ -198,6 +198,9 @@ func drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) {
 		// z is in [1, -1]
 		rate := float64(j) / float64(ph)
 		z := (1-rate)*1 + rate*-1
+		if z <= 0 {
+			break
+		}
 		op := &ebiten.DrawImageOptions{}
 		op.GeoM.Translate(-float64(pw)/2, 0)
 		op.GeoM.Scale(1/z, 8) // 8 is an arbitrary number not to make empty lines.