diff --git a/README.md b/README.md
index 50d429a..8923908 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,9 @@ the `V` key.  Rows and columns are now stored as sorted lists intead
 of sets.  Rows and columns are now in a consistent order in the file
 export.  Performance boosts in bit marking, background bit marking and
 alignment.  Universal binary for macOS.  RomAlignerTilting works
-better for designs with a gap between banks.
+better for designs with a gap between banks.  Out-of-view bits are no
+longer drawn during dragging, speeding up adjusting groups of long
+lines.
 
 2024-07-14 -- Fixes crash when deleting a double-selected item.  Delete
 and backspace now delete objects like `D`.  Multiple disassemblers.
diff --git a/maskromtool.cpp b/maskromtool.cpp
index 73988d8..8700036 100644
--- a/maskromtool.cpp
+++ b/maskromtool.cpp
@@ -1401,6 +1401,11 @@ void MaskRomTool::markBit(RomLineItem* row, RomLineItem* col){
 
     //This rectangle will be a small box around the pixel.
     QPointF point=bitLocation(row, col);
+    //When dragging, skip anything that's not immediately visible.
+    if(dragging && !isPointVisible(point))
+        return;
+
+
     RomBitItem *bit=new RomBitItem(point, bitSize, row, col);
     scene->addItem(bit);
     bit->setVisible(bitsVisible);
@@ -1534,6 +1539,24 @@ static bool colthroughrect(QLineF line, QRectF rect){
     return false;
 }
 
+//Is a point visible?  Handy when dragging.
+bool MaskRomTool::isPointVisible(QPointF p){
+    //Primary view.
+    QRectF rect=view->mapToScene(view->viewport()->rect()).boundingRect();
+    if(p.x()<rect.right() && p.x()>rect.left()
+        && p.y()>rect.top() && p.y()<rect.bottom())
+        return true;
+
+    //Secondary view, only if visible.
+    if(!second.isVisible()) return false;
+    rect=second.view->mapToScene(second.view->viewport()->rect()).boundingRect();
+    if(p.x()<rect.right() && p.x()>rect.left()
+        && p.y()>rect.top() && p.y()<rect.bottom())
+        return true;
+
+    return false;
+}
+
 //Mark up all of the bits where rows and columns collide.
 bool MaskRomTool::markBits(bool full){
     bool bitswerevisible=bitsVisible;
diff --git a/maskromtool.h b/maskromtool.h
index 547d6a4..d3a235d 100644
--- a/maskromtool.h
+++ b/maskromtool.h
@@ -98,6 +98,7 @@ class MaskRomTool : public QMainWindow{
      * hogging the rendering thread.
      */
     enum {STATE_IDLE, STATE_CLEARING, STATE_MARKING} state=STATE_IDLE;
+    bool dragging=false; //Only mark visible bits when true.
 
     //Marks all of the bit positions, but not their connections.
     bool markBits(bool full=true);
@@ -121,6 +122,8 @@ class MaskRomTool : public QMainWindow{
     void moveList(QList<QGraphicsItem*> list, QPointF offset);
     //Inserts a new line, either row or column.
     bool insertLine(RomLineItem* line);
+    //Is a point visible?  Handy when dragging.
+    bool isPointVisible(QPointF p);
 
     //Get a bit at a point.
     RomBitItem* getBit(QPointF point);
diff --git a/romscene.cpp b/romscene.cpp
index 917a204..87c58cc 100644
--- a/romscene.cpp
+++ b/romscene.cpp
@@ -192,6 +192,7 @@ void RomScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent){
 
     //Right mouse can drag a line, so we mark an undo point before moving.
     if(mouseEvent->buttons()==Qt::RightButton){
+        maskRomTool->dragging=true;
         maskRomTool->markUndoPoint();
         maskRomTool->clearBits(false);
     }
@@ -222,7 +223,6 @@ void RomScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent){
         //qDebug()<<"Selection: "<<x<<y<<w<<h;
 
         auto newselection=items(x, y, w, h,
-
                           //Qt::ItemSelectionMode::ContainsItemBoundingRect,  //Useful for bits.
                           //Qt::ItemSelectionMode::ContainsItemShape, // Only when fully covered.
                           //Qt::ItemSelectionMode::IntersectsItemBoundingRect,  //Useful for a near miss, sometimes too wide.
@@ -278,6 +278,7 @@ void RomScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent){
          * arrangement.  As a workaround, we remark the bits after releasing the
          * button from a moving drag.
          */
+        maskRomTool->dragging=false;
         if(maskRomTool->bitsVisible){
             //Clear the old bits in the background.
             //This will continue until redrawing them.