Use OrthogonalLayout to generate initial placement for SpringLayout

In a series of posts we’ll explore ways to combine graph layout algorithms for various purposes, such as improving layout speed or achieving specific layout constraints.

In this example we’ll show how to apply OrthogonalLayout as preprocessing step for SpringLayout used to minimize edge crossings. A problem with force-directed layout algorithms such as SpringLayout is that they can reach equilibrium of the simulated forces while there are link crossings present. However if the simulation starts from an initial layout that has minimal number of crossing, it will tend to reach balance without introducing new crossings. So we can use any of the layout algorithms used for arranging planar graphs (OrthogonalLayout, TriangularLayout, CascadingLayout) to create the initial configuration for SpringLayout.

OrthogonalLayout is designed to create planar drawings of graphs (having no crossing links at all if possible) where edge segments are either horizontal or vertical. For some types of diagrams, such as flowcharts, you might use OrthogonalLayout as is. However in many cases you might prefer SpringLayout, e.g. in order to achieve aesthetic criteria like uniform edge lengths, or to conform to accepted drawing conventions such as the one used to present state machines. So when you know your graphs are planar or close to planar, you can run OrthogonalLayout as pre-processing step, and then run the physical-force simulation using SpringLayout to achieve straight-line uniform length drawings:

void ApplySpringLayout(bool preArrange)
{
    if (preArrange)
    {
        var tl = new OrthogonalLayout();
        tl.Arrange(diagram);
    }

    var sl = new SpringLayout();
    sl.Randomize = false;
    sl.MinimizeCrossings = true;
    sl.IterationCount = 50;
    sl.Arrange(diagram);

    diagramView.ZoomToFit();
}

Here are several examples of the method results when called respectively with false (on the left side) and with true (on the right side of image). Note that for such small graphs SpringLayout will probably remove the crossings if left to run for more iterations, but in the general case and with larger graphs that’s not guaranteed.

The code above uses MindFusion’s .NET API and can be used with Windows Forms, WPF, Silverlight and ASP.NET diagramming components. The Java API for Android and desktop Swing application will look similar, with setter method calls instead of property assignments.

Enjoy!

In this post we’ll show how to create custom formula shapes with adjustable control points. Shape control points are a new feature in version 6.1 of the Flowchart.NET control, which is currently in beta tests. You can download a copy of the beta version from the following link.

https://mindfusion.dev/_beta/DiagWinForms61.zip

A shape formula is defined using a script, which calls one of the following functions to draw the node shape.

For example, the following formula defines a rounded rectangle shape using lines and arcs, and expects to receive a “radius” control point parameter that will control the corner radii:

// a rounded rectangle shape, with an arc at each corner
string roundRect = @"
	r = Min(Width / 2, radius.X);
	MoveTo(r, 0);
	LineTo(Width - r, 0);
	ArcTo(Width, r, false, false, r, r);
	LineTo(Width, Height - r);
	ArcTo(Width - r, Height, false, false, r, r);
	LineTo(r, Height);
	ArcTo(0, Height - r, false, false, r, r);
	LineTo(0, r);
	ArcTo(r, 0, false, false, r, r);
 ";

When creating a Shape instance, we must add a ShapeControlPoint object to it that defines the radius parameter and its constraints. The following code specifies that the default radius is 5, the minimum and maximum values allowed are 1 and 15 respectively, and prevents the control point from moving vertically by setting minY and maxY to 0.

var myRect = new Shape(roundRect, "MyRect");

// add a control point for the 'radius' parameter
myRect.ControlPoints.Add(new ShapeControlPoint(
	"radius", 5, 1, 15, UnitType.Fixed, 0, 0, 0, UnitType.Fixed));

Here is another example that defines an anchor-like shape with two parameters controlling the tips of the anchor arms.

// an anchor shape, with two arcs outlining each anchor arm
string anchor = @"
	r = Width / 3;
	y1 = p1.Y * Height / 100;
	y2 = p2.Y * Height / 100;
	MoveTo(Width / 2, Height);
	MoveTo(Width / 2 + 3, Height - 5);
	ArcTo(Width, y2, false, true, r, r);
	ArcTo(Width / 2 + 3, Height - 10, false, false, r, r);
	LineTo(Width / 2 + 3, 0);
	LineTo(Width / 2 - 3, 0);
	LineTo(Width / 2 - 3, Height - 10);
	ArcTo(0, y1, false, false, r, r);
	ArcTo(Width / 2 - 3, Height - 5, false, true, r, r);
	LineTo(Width / 2, Height);
 ";

var myAnchor = new Shape(anchor, "MyAnchor");

// add control points at the tips of anchor arms
myAnchor.ControlPoints.Add(new ShapeControlPoint(
	"p1", 0, 0, 0, UnitType.Percentage, 55, 50, 80, UnitType.Percentage));
myAnchor.ControlPoints.Add(new ShapeControlPoint(
	"p2", 100, 100, 100, UnitType.Percentage, 55, 50, 80, UnitType.Percentage));

The following diagram contains several nodes displaying the shapes above, with some of the control points moved to different positions.

Some additional functions that you can call from shape scripts are listed below.

The complete sample project is available for download here:
https://mindfusion.dev/_samples/ParamShapes.zip

Enjoy!