implemented graphviz builderin dot.go to build dot files for graphviz

internal/viz/dot.go

@@ -1,3 +1,37 @@
 package viz
 
-//init
+import (
+	"bspviz/internal/bsp"
+	"bytes"
+	"fmt"
+	"os"
+)
+
+func EmitDOT(root *bsp.Node, path string) error {
+	var buf bytes.Buffer
+	buf.WriteString("digraph BSP {\n")
+	buf.WriteString("  node [fontname=\"Helvetica\"];\n")
+
+	id := 0
+	var walk func(*bsp.Node) int
+	walk = func(n *bsp.Node) int {
+		my := id
+		id++
+		if n.Leaf != nil {
+			fmt.Fprintf(&buf, "  n%d [label=\"Leaf\\nSegs=%d\", shape=ellipse, style=filled, fillcolor=lightgray];\n",
+				my, len(n.Leaf.Segs))
+			return my
+		}
+		fmt.Fprintf(&buf, "  n%d [label=\"Split\\nO=(%.0f,%.0f) D=(%.0f,%.0f)\"];\n",
+			my, n.O.X, n.O.Y, n.D.X, n.D.Y)
+		l := walk(n.Left)
+		r := walk(n.Right)
+		fmt.Fprintf(&buf, "  n%d -> n%d [label=\"L\"];\n", my, l)
+		fmt.Fprintf(&buf, "  n%d -> n%d [label=\"R\"];\n", my, r)
+		return my
+	}
+	walk(root)
+
+	buf.WriteString("}\n")
+	return os.WriteFile(path, buf.Bytes(), 0644)
+}