JAL-3002 don't use fastPaint for page up/down

diff --git a/src/jalview/gui/SeqCanvas.java b/src/jalview/gui/SeqCanvas.java
index 2d8eb7d..c89ba56 100755 (executable)
--- a/src/jalview/gui/SeqCanvas.java
+++ b/src/jalview/gui/SeqCanvas.java
@@ -1740,7 +1740,7 @@ public class SeqCanvas extends JComponent implements ViewportListenerI
       }
       ViewportRanges vpRanges = av.getRanges();
 
-      int range = vpRanges.getEndRes() - vpRanges.getStartRes();
+      int range = vpRanges.getEndRes() - vpRanges.getStartRes() + 1;
       if (scrollX > range)
       {
         scrollX = range;
@@ -1809,10 +1809,10 @@ public class SeqCanvas extends JComponent implements ViewportListenerI
   {
     ViewportRanges ranges = av.getRanges();
 
-    if (Math.abs(scrollX) > ranges.getViewportWidth())
+    if (Math.abs(scrollX) >= ranges.getViewportWidth())
     {
       /*
-       * shift of more than one view width is 
+       * shift of one view width or more is 
        * overcomplicated to handle in this method
        */
       fastPaint = false;
@@ -2003,10 +2003,17 @@ public class SeqCanvas extends JComponent implements ViewportListenerI
 
       while (y >= 0)
       {
+        /*
+         * shift 'widthToCopy' residues by 'positions' places to the right
+         */
         gg.copyArea(copyFromLeftStart, y, widthToCopy, heightToCopy,
                 positions * charWidth, 0);
         if (y > 0)
         {
+          /*
+           * copy 'positions' residue from the row above (right hand end)
+           * to this row's left hand end
+           */
           gg.copyArea(copyFromRightStart, y - wrappedRepeatHeightPx,
                   positions * charWidth, heightToCopy, -widthToCopy,
                   wrappedRepeatHeightPx);