JAL-1722 fix: don’t draw visible regions outside viewport view

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

diff --git a/src/jalview/gui/SeqCanvas.java b/src/jalview/gui/SeqCanvas.java
index 5706fe7..0f24b4b 100755 (executable)
--- a/src/jalview/gui/SeqCanvas.java
+++ b/src/jalview/gui/SeqCanvas.java
@@ -335,6 +335,7 @@ public class SeqCanvas extends JComponent
    */
 
   // Set this to false to force a full panel paint
+  @Override
   public void paintComponent(Graphics g)
   {
     updateViewport();
@@ -682,10 +683,17 @@ public class SeqCanvas extends JComponent
         g1.translate(-screenY * charWidth, 0);
         screenY += blockEnd - blockStart + 1;
         blockStart = hideEnd + 1;
+
+        if (screenY > (endRes - startRes))
+        {
+          // already rendered last block
+          return;
+        }
       }
 
       if (screenY <= (endRes - startRes))
       {
+        // remaining visible region to render
         blockEnd = blockStart + (endRes - startRes) - screenY;
         g1.translate(screenY * charWidth, 0);
         draw(g1, blockStart, blockEnd, startSeq, endSeq, offset);