JAL-147 don't scroll up beyond startRes = 0

[jalview.git] / src / jalview / gui / AlignmentPanel.java

diff --git a/src/jalview/gui/AlignmentPanel.java b/src/jalview/gui/AlignmentPanel.java
index a732527..e62707f 100644 (file)
--- a/src/jalview/gui/AlignmentPanel.java
+++ b/src/jalview/gui/AlignmentPanel.java
@@ -809,14 +809,14 @@ public class AlignmentPanel extends GAlignmentPanel implements
       {
         return;
       }
-      else if (newY > -1)
+      if (newY > -1)
       {
         /*
          * limit page up/down to one width's worth of positions
          */
         int rowSize = vpRanges.getViewportWidth();
         int newX = newY > oldY ? oldX + rowSize : oldX - rowSize;
-        vpRanges.setViewportStartAndWidth(newX, rowSize);
+        vpRanges.setViewportStartAndWidth(Math.max(0, newX), rowSize);
       }
     }
     else