Redraw problems when scrolling with ScrollGraphicalViewer

Question

Environment: Eclipse Neon on Win10.

I have an older GEF/SWT RCP application that uses a ScrollingGraphicalViewer to handle scrolling. When I scroll, the original image that should be preserved in the scroll is moved properly, but the new area is not drawn. Sometimes, minimizing and restoring the application window gets it to redraw correctly. although at other times, it will show the image as if it hadn't been scrolled, but the scroll bar indicates that it has.

This happens with both horizontal and vertical scrolling. I'm only testing with thumb scrolling because it's a single move rather than a continuous operation with lots of redraws.

Here's a code sample. It's the paintFigure() method from one of my figures that goes the full width.

      protected void paintFigure (Graphics graphics)
      {
        if (log.isTraceEnabled ()) {
          final Rectangle dummy = new Rectangle ();
          log.trace (String.format ("Paint rung %s, bounds %s, clip %s", rungId.getText (), getBounds (), graphics.getClip (dummy))); //$NON-NLS-1$
        }
        super.paintFigure (graphics);

        // Draw the vertical bars
        Rectangle r = getBounds ().getCopy ();
        r.width -= LINE_WIDTH;
        r.width += 1; // Coming up 1 short for some reason
        r.shrink (MARGIN, 0);
        if (log.isTraceEnabled ()) {
          log.trace (String.format ("Adjusted bounds %s", r)); //$NON-NLS-1$
        }
        final int connectionY = r.y + connectionYOffset;
        int connectionXStart = instructionsFigure.getBounds ().right ();
        int connectionXStop = r.right ();
        graphics.drawLine (connectionXStart, connectionY, connectionXStop, connectionY);
        connectionXStart = r.x-4;
        connectionXStop = instructionsFigure.getBounds ().x;
        graphics.drawLine (connectionXStart, connectionY, connectionXStop, connectionY);

        graphics.setLineWidth (LINE_WIDTH);
        graphics.drawLine (r.getTopRight (), r.getBottomRight ());

        graphics.drawLine (r.x - 4, r.y, r.x - 4, r.y+r.height);
      }

Here is some trace output. Note that LadderLayer is the parent figure to the Rung.

Initial display:
TRACE   2018-06-30 10:08:56,289 10099   com.bas.basplc.ui.editors.ladder_editor.figures.LadderLayer [main]  Paint ladder layer, bounds Rectangle(0.0, 0.0, 1200.0, 2190.0), clip Rectangle(0.0, 0.0, 1070.0, 673.0)
TRACE   2018-06-30 10:08:56,289 10099   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Paint rung 0, bounds Rectangle(3.0, 3.0, 1200.0, 384.0), clip Rectangle(3.0, 3.0, 1067.0, 384.0)
TRACE   2018-06-30 10:08:56,290 10100   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Adjusted bounds Rectangle(63.0, 3.0, 1078.0, 384.0)
Not sure what is being drawn here:
TRACE   2018-06-30 10:08:56,370 10180   com.bas.basplc.ui.editors.ladder_editor.figures.LadderLayer [main]  Paint ladder layer, bounds Rectangle(0.0, 0.0, 1200.0, 2190.0), clip Rectangle(1047.0, 15.0, 23.0, 658.0)
TRACE   2018-06-30 10:08:56,370 10180   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Paint rung 0, bounds Rectangle(3.0, 3.0, 1200.0, 384.0), clip Rectangle(1047.0, 15.0, 23.0, 372.0)
TRACE   2018-06-30 10:08:56,370 10180   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Adjusted bounds Rectangle(63.0, 3.0, 1078.0, 384.0)
Thumb scroll right:
TRACE   2018-06-30 10:10:16,244 90054   com.bas.basplc.ui.editors.ladder_editor.figures.LadderLayer [main]  Paint ladder layer, bounds Rectangle(0.0, 0.0, 1200.0, 2190.0), clip Rectangle(940.0, 0.0, 130.0, 673.0)
TRACE   2018-06-30 10:10:16,245 90055   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Paint rung 0, bounds Rectangle(3.0, 3.0, 1200.0, 384.0), clip Rectangle(940.0, 3.0, 130.0, 384.0)
TRACE   2018-06-30 10:10:16,245 90055   com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Adjusted bounds Rectangle(63.0, 3.0, 1078.0, 384.0)
Redraw after minimize/restore:
TRACE   2018-06-30 10:11:56,406 190216  com.bas.basplc.ui.editors.ladder_editor.figures.LadderLayer [main]  Paint ladder layer, bounds Rectangle(0.0, 0.0, 1200.0, 2190.0), clip Rectangle(0.0, 0.0, 1070.0, 673.0)
TRACE   2018-06-30 10:11:56,406 190216  com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Paint rung 0, bounds Rectangle(3.0, 3.0, 1200.0, 384.0), clip Rectangle(3.0, 3.0, 1067.0, 384.0)
TRACE   2018-06-30 10:11:56,407 190217  com.bas.basplc.ui.editors.ladder_editor.figures.RungFigure  [main]  Adjusted bounds Rectangle(63.0, 3.0, 1078.0, 384.0)

Before the thumb scroll:

After the thumb scroll:

Answer 1

Solved! I was using SimpleRootEditPart, Viewport, LayeredPane, Layer, AbstractLayout. Switching to the Freeform versions of these and I can now scroll cleanly.