Redrawing the grapher after layout

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When a layout algorithm is executed, it moves the nodes and/or reshapes the links of the graph. If the graph is displayed on a screen, its display must be updated to reflect the changes made by the layout.

If you use a diagram component (a subclass of IlvDiagrammer)), the updating is done automatically.
If you call layout by using the method performLayout , you have more detailed control on the redraw mechanism, as explained in the following sections:

Rogue Wave® JViews provides complete flexibility, concerning the redraw of an IlvGrapher instance that has undergone layout. Your choice will depend on your particular application. The following scenarios are possible:

Automatic and selective redraw

If you just want the grapher to be automatically redrawn after the layout, simply call the following method with the value true for the redraw argument:

IlvGraphLayoutReport performLayout(boolean force, boolean redraw)

When you do this, an initReDraws/ reDrawViews session is initiated automatically. When the nodes and the links are moved or reshaped, the value true is passed for the redraw argument of the appropriate methods of IlvGrapher. At the end of the layout, the initReDraws/reDrawViews session is ended. This produces a selective redraw of the invalid regions of the views where the graph is displayed.

Nonautomatic and complete redraw

If all the nodes are moved by the layout, it may be more efficient to redraw the entire graph at the end of the layout instead of using the mechanism of the invalid regions provided by IlvGrapher . In this case, you can use the following code:

try {
  layout.performLayout(false, false); // argument redraw at false
} catch (IlvGraphLayoutException e) {
  e.printStackTrace();
} finally {
  // redraw in the final clause to ensure that the redraw
  // is performed even if an exception occurs
  grapher.reDraw();
}

This completely redraws the grapher in all its visible views. Alternatively, you can call the method repaint on some of its views.

Delayed redraw

After the layout, you may want to perform other changes in the grapher before redrawing. You can start the initReDraws/ reDrawViews session on your own to control the point in time when the redraw is performed. You can use the following code:

grapher.initReDraws();
try {
  layout.performLayout(false, true);
} catch (IlvGraphLayoutException e) {
  e.printStackTrace();
} finally {
  grapher.moveObject(..., false); // some other changes in the grapher
  grapher.reDrawViews();
}

No redraw at all

Sometimes, the layout may need to be performed without any display of the grapher. For instance, this can be done to automatically produce .ivl files containing the result of the layout for future use. To avoid any redraw during the layout, just call the method performLayout with the value false for the redraw argument.

Note

During animated layout (for layouts supporting this option), the grapher needs to be redrawn after each step to produce the animation effect. Therefore, you need to pass the value true for the redraw argument of the method performLayout. In this case, the initReDraws/ reDrawViews session is automatically used for each animation step. Users should not add their own initReDraw/reDrawViews session because this would prevent the graph from being redrawn during the animation.

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