From d39a948bd472da39428d4f267462680463e4ad3c Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Sun, 21 Sep 2014 09:04:59 +0200
Subject: [PATCH] mtseeder: Fixed problem that tiles with missing sub tiles
 were drawn in white entirely.

---
 cmd/mtseeder/pyramid.go | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/cmd/mtseeder/pyramid.go b/cmd/mtseeder/pyramid.go
index 0f48bdf..edde0a4 100644
--- a/cmd/mtseeder/pyramid.go
+++ b/cmd/mtseeder/pyramid.go
@@ -136,6 +136,22 @@ func createParentLevel(oldDir string, jobs chan pyramidJob) (newDir string, err
 	return
 }
 
+func clip8(x int) int {
+	switch {
+	case x < 0:
+		return 0
+	case x > 256:
+		return 256
+	}
+	return x
+}
+
+func clipRect(r image.Rectangle) image.Rectangle {
+	return image.Rectangle{
+		Min: image.Point{X: clip8(r.Min.X), Y: clip8(r.Min.Y)},
+		Max: image.Point{X: clip8(r.Max.X), Y: clip8(r.Max.Y)}}
+}
+
 var dps = [4]image.Point{
 	image.Pt(0, 256),
 	image.Pt(0, 0),
@@ -148,7 +164,7 @@ func fuseTile(scratch *image.RGBA, job *pyramidJob) (err error) {
 
 		img := common.LoadPNG(path)
 
-		sr := img.Bounds()
+		sr := clipRect(img.Bounds())
 		r := sr.Sub(sr.Min).Add(dps[i])
 
 		draw.Draw(scratch, r, img, sr.Min, draw.Src)