Question

So there is a great open source tutorial on creating TreeNode class. It is great. But I wonder how to change its Arrange function to make it draw indented tree?

Here’s the function:

// Arrange the node and its children in the allowed area.
// Set xmin to indicate the right edge of our subtree.
// Set ymin to indicate the bottom edge of our subtree.
public void Arrange(Graphics gr, ref float xmin, ref float ymin)
{
    // See how big this node is.
    SizeF my_size = Data.GetSize(gr, MyFont);

    // Recursively arrange our children,
    // allowing room for this node.
    float x = xmin;
    float biggest_ymin = ymin + my_size.Height;
    float subtree_ymin = ymin + my_size.Height + Voffset;
    foreach (TreeNode<T> child in Children)
    {
        // Arrange this child's subtree.
        float child_ymin = subtree_ymin;
        child.Arrange(gr, ref x, ref child_ymin);

        // See if this increases the biggest ymin value.
        if (biggest_ymin < child_ymin) biggest_ymin = child_ymin;

        // Allow room before the next sibling.
        x += Hoffset;
    }

    // Remove the spacing after the last child.
    if (Children.Count > 0) x -= Hoffset;

    // See if this node is wider than the subtree under it.
    float subtree_width = x - xmin;
    if (my_size.Width > subtree_width)
    {
        // Center the subtree under this node.
        // Make the children rearrange themselves
        // moved to center their subtrees.
        x = xmin + (my_size.Width - subtree_width) / 2;
        foreach (TreeNode<T> child in Children)
        {
            // Arrange this child's subtree.
            child.Arrange(gr, ref x, ref subtree_ymin);

            // Allow room before the next sibling.
            x += Hoffset;
        }

        // The subtree's width is this node's width.
        subtree_width = my_size.Width;
    }

    // Set this node's center position.
    Center = new PointF(
        xmin + subtree_width / 2,
        ymin + my_size.Height / 2);

    // Increase xmin to allow room for
    // the subtree before returning.
    xmin += subtree_width;

    // Set the return value for ymin.
    ymin = biggest_ymin;
}

How it looks now:

How indented tree looks like ( image based on DmitryG s grate answer):

So.. How do I make it draw the graph in the indented form?

Answer 1

I have modified the TreeNode.Arrange() method for indented tree arrangement.

Now it looks like this:

public void Arrange(Graphics gr, ref float xmin, ref float ymin) {
    // See how big this node is.
    SizeF my_size = Data.GetSize(gr, MyFont);
    // Recursively arrange our children,
    // allowing room for this node.
    float y = ymin + my_size.Height;
    float biggest_xmin = xmin + my_size.Width;
    float subtree_xmin = xmin + my_size.Width + Hoffset;
    foreach(TreeNode<T> child in Children) {
        // Arrange this child's subtree.
        float child_xmin = subtree_xmin;
        child.Arrange(gr, ref child_xmin, ref y);
        // See if this increases the biggest ymin value.
        if(biggest_xmin < child_xmin) biggest_xmin = child_xmin;
        // Allow room before the next sibling.
        y += Voffset;
    }
    // Remove the spacing after the last child.
    if(Children.Count > 0) y -= Voffset;
    // See if this node is wider than the subtree under it.
    float subtree_height = y - ymin;
    if(my_size.Height > subtree_height) {
        y = ymin + (my_size.Height - subtree_height) / 2;
        foreach(TreeNode<T> child in Children) {
            // Arrange this child's subtree.
            child.Arrange(gr, ref subtree_xmin, ref y);
            y += Voffset;
        }
        subtree_height = my_size.Height;
    }
    // Set this node's center position.
    Center = new PointF(xmin + my_size.Width / 2, ymin + my_size.Height / 2);
    ymin += subtree_height;
    xmin = biggest_xmin;
}

Note, that the DrawSubtreLinks() method have also been modified:

private void DrawSubtreeLinks(Graphics gr) {
    foreach(TreeNode<T> child in Children) {
        PointF p = new PointF(Center.X, child.Center.Y);
        gr.DrawLine(MyPen, Center, p);
        gr.DrawLine(MyPen, p, child.Center);
        child.DrawSubtreeLinks(gr);
    }
}