fix wrap alignment vscroll visible amount

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

diff --git a/src/jalview/gui/SeqCanvas.java b/src/jalview/gui/SeqCanvas.java
index 698489e..c243a2e 100755 (executable)
--- a/src/jalview/gui/SeqCanvas.java
+++ b/src/jalview/gui/SeqCanvas.java
@@ -115,7 +115,7 @@ public class SeqCanvas extends JPanel
 \r
 public void fastPaint(int horizontal, int vertical)\r
 {\r
-    if (horizontal == 0 && vertical == 0)\r
+    if (horizontal == 0 && vertical == 0 || gg==null)\r
       return;\r
 \r
     gg.copyArea(0, 0, imgWidth, imgHeight, -horizontal * av.charWidth,\r
@@ -133,11 +133,19 @@ public void fastPaint(int horizontal, int vertical)
 \r
     else if (vertical > 0) // scroll down\r
     {\r
-      transY = imgHeight - vertical * av.charHeight;\r
       ss = es - vertical;\r
+      if(ss<av.startSeq) // ie scrolling too fast, more than a page at a time\r
+        ss = av.startSeq;\r
+      else\r
+        transY = imgHeight - vertical * av.charHeight;\r
     }\r
     else if (vertical < 0)\r
+    {\r
       es = ss - vertical;\r
+      if(es > av.endSeq)\r
+        es = av.endSeq;\r
+    }\r
+\r
 \r
     gg.translate(transX, transY);\r
 \r