/// <summary>
/// Draws a branch in a tree. This function is recursive.
/// </summary>
/// <param name="branch">the branch to draw</param>
/// <param name="graphics">allows graphics to be drawn</param>
/// <param name="pen">for drawing lines</param>
/// <param name="nodeFill">for drawing nodes</param>
/// <param name="direction">the side of the tree the node is drawn on</param>
/// <param name="slotsUsed">the number of slots on this side of the tree that have already been used</param>
/// <param name="pixelsPerSlot">the number of pixels in a slot</param>
/// <param name="parentPositionX">the x-position of this branch's parent</param>
private void drawBranch(TreeNode branch, Graphics graphics, Pen pen, Brush nodeFill, int direction, int slotsUsed, float pixelsPerSlot, float parentPositionX)
{
// calculate some useful numbers
int slotsInThisBranch = branch.GetNumChildlessDescendents();
float nodeCenterX = (this.Width / 2) + (direction * (slotsUsed + ((slotsInThisBranch + 1) / 2)) * pixelsPerSlot);
// draw this node
graphics.FillEllipse(nodeFill, nodeCenterX - (NODE_DIAMETER / 2), ValueToYCoordinate(branch.value) - (NODE_DIAMETER / 2), NODE_DIAMETER, NODE_DIAMETER);
// draw lines from the branch node back to its parent
graphics.DrawLine(pen, parentPositionX, ValueToYCoordinate(branch.GetParents()[0].value), nodeCenterX, ValueToYCoordinate(branch.GetParents()[0].value));
graphics.DrawLine(pen, nodeCenterX, ValueToYCoordinate(branch.GetParents()[0].value), nodeCenterX, ValueToYCoordinate(branch.value));
int slotsUsedAfterChild = slotsUsed;
foreach (TreeNode parent in branch.GetChildren()) {
drawBranch(parent, graphics, pen, nodeFill, direction, slotsUsedAfterChild, pixelsPerSlot, nodeCenterX);
slotsUsedAfterChild += parent.GetNumChildlessDescendents(); }
}