JAL-2774 Fix repaint artefacts

diff --git a/src/jalview/gui/SeqCanvas.java b/src/jalview/gui/SeqCanvas.java
index 58af47b..7724592 100755 (executable)
--- a/src/jalview/gui/SeqCanvas.java
+++ b/src/jalview/gui/SeqCanvas.java
@@ -296,47 +296,48 @@ public class SeqCanvas extends JComponent implements ViewportListenerI
       int transX = 0;
       int transY = 0;
 
-    gg.copyArea(horizontal * charWidth, vertical * charHeight,
-            img.getWidth(), img.getHeight(), -horizontal * charWidth,
-            -vertical * charHeight);
+      gg.copyArea(horizontal * charWidth, vertical * charHeight,
+              img.getWidth(), img.getHeight(), -horizontal * charWidth,
+              -vertical * charHeight);
 
-    if (horizontal > 0) // scrollbar pulled right, image to the left
-    {
-      transX = (endRes - startRes - horizontal) * charWidth;
-      startRes = endRes - horizontal;
-    }
-    else if (horizontal < 0)
-    {
-      endRes = startRes - horizontal;
-    }
-    else if (vertical > 0) // scroll down
-    {
-      startSeq = endSeq - vertical;
-
-      if (startSeq < ranges.getStartSeq())
-      { // ie scrolling too fast, more than a page at a time
-        startSeq = ranges.getStartSeq();
+      if (horizontal > 0) // scrollbar pulled right, image to the left
+      {
+        transX = (endRes - startRes - horizontal) * charWidth;
+        startRes = endRes - horizontal;
       }
-      else
+      else if (horizontal < 0)
       {
-        transY = img.getHeight() - ((vertical + 1) * charHeight);
+        endRes = startRes - horizontal;
       }
-    }
-    else if (vertical < 0)
-    {
-      endSeq = startSeq - vertical;
 
-      if (endSeq > ranges.getEndSeq())
+      if (vertical > 0) // scroll down
+      {
+        startSeq = endSeq - vertical;
+
+        if (startSeq < ranges.getStartSeq())
+        { // ie scrolling too fast, more than a page at a time
+          startSeq = ranges.getStartSeq();
+        }
+        else
+        {
+          transY = img.getHeight() - ((vertical + 1) * charHeight);
+        }
+      }
+      else if (vertical < 0)
       {
-        endSeq = ranges.getEndSeq();
+        endSeq = startSeq - vertical;
+
+        if (endSeq > ranges.getEndSeq())
+        {
+          endSeq = ranges.getEndSeq();
+        }
       }
-    }
 
-    gg.translate(transX, transY);
-    drawPanel(gg, startRes, endRes, startSeq, endSeq, 0);
-    gg.translate(-transX, -transY);
+      gg.translate(transX, transY);
+      drawPanel(gg, startRes, endRes, startSeq, endSeq, 0);
+      gg.translate(-transX, -transY);
 
-    repaint();
+      repaint();
     } finally
     {
       fastpainting = false;
@@ -1711,8 +1712,11 @@ public class SeqCanvas extends JComponent implements ViewportListenerI
       }
       else if (eventName.equals(ViewportRanges.STARTRESANDSEQ))
       {
-        fastPaint(scrollX, ((int[]) evt.getNewValue())[1]
-                - ((int[]) evt.getOldValue())[1]);
+        fastPaint(scrollX, 0);
+        // bizarrely, we only need to scroll on the x value here as fastpaint
+        // copies the full height of the image anyway. Passing in the y value
+        // causes nasty repaint artefacts, which only disappear on a full
+        // repaint.
       }
     }
   }