Add ability to render more than one tree

main.go

@@ -42,7 +42,7 @@ func main() {
 	}
 	defer termui.Close()
 
-	tree := NewTreeWidget([]*Node{buildTree(0)})
+	tree := NewTreeWidget([]*Node{buildTree(0), buildTree(0)})
 	width, height := termui.TerminalDimensions()
 	tree.SetRect(0, 0, width, height)
 	tree.Block.Border = true

tree.go

@@ -41,8 +41,9 @@ func NewTreeWidget(rootNodes []*Node) *TreeWidget {
 // Draw draws the tree widget
 func (tree *TreeWidget) Draw(buffer *termui.Buffer) {
 	tree.Block.Draw(buffer)
+	row := tree.Block.Inner.Min.Y
 	for _, item := range tree.rootNodes {
-		tree.renderSingleTree(item, buffer)
+		row = tree.renderSingleTree(item, buffer, row)
 	}
 }
 
@@ -50,7 +51,7 @@ func (tree *TreeWidget) Draw(buffer *termui.Buffer) {
 func (tree *TreeWidget) AddRootNode(node *Node) {
 	tree.rootNodes = append(tree.rootNodes, node)
 	if len(tree.rootNodes) == 1 {
-		tree.selectedNode = node
+		tree.selectedNode = node.children[0]
 	}
 	node.setTree(tree)
 }
@@ -74,12 +75,14 @@ func (tree *TreeWidget) SelectNext() {
 	}
 }
 
-func (tree *TreeWidget) renderSingleTree(root *Node, buffer *termui.Buffer) {
+// renderSingleTree renders a node and all its descendents
+// Returns the number of rows needed to render it (inculding wrapping)
+func (tree *TreeWidget) renderSingleTree(root *Node, buffer *termui.Buffer, startRow int) int {
 	baseWidth := tree.Inner.Max.X - tree.Inner.Min.X
 
 	depths := map[*Node]int{root: 0}
 	toVisit := []*Node{root}
-	row := tree.Inner.Min.Y
+	row := startRow
 	for len(toVisit) > 0 {
 		var node *Node
 		toVisit, node = toVisit[:len(toVisit)-1], toVisit[len(toVisit)-1]
@@ -97,6 +100,8 @@ func (tree *TreeWidget) renderSingleTree(root *Node, buffer *termui.Buffer) {
 		startingCol := tree.Inner.Min.X + currentDepth*indentWidth
 		row += node.render(buffer, row, startingCol, width)
 	}
+
+	return row
 }
 
 // render renders this node in the term ui, and return the number of rows that were required to render it