Doing some cleanup and refactoring.

I've added some extension methods so that adding the commands is cleaner and less error prone (I kept forgetting the semicolons.).

settings.gradle

@@ -1,2 +1,2 @@
-rootProject.name = 'openrndr-template'
+rootProject.name = 'openrndr-hpgl'
 

src/main/kotlin/com/martianwabbit/hpglWriter.kt

@@ -16,64 +16,64 @@ class HPGL(
     private val height: Int = 0
 ) {
     fun generateFromComposition(composition: Composition): String {
-        val result = StringBuilder()
+        val hpgl = StringBuilder()
 
-        result.appendln("IN;") // Initialize the plotter
+        hpgl.cmd("IN")
 
-        // Setup coordinates
+        // Setup plotter coordinates
         if (p1 != Vector2.ZERO || p2 != Vector2.ZERO) {
-            result.appendln("IP${p1.getCoords()},${p2.getCoords()};")
+            hpgl.cmd("IP", p1, p2)
         }
 
         // Setup scaling
+        // If no width and height is provided it'll default to the plotter's scaling.
+        // Ideally this should always be the screen width and height as that'll make it
+        // so that everything scales correctly from the screensize into the page size.
         if (width == 0 && height == 0) {
-            result.appendln("SC;")
+            hpgl.cmd("SC")
         } else {
-            result.appendln("SC0,$width,0,$height;")
+            hpgl.cmd("SC", Vector2(.0, width.toDouble()), Vector2(.0, height.toDouble()))
         }
 
-        result.appendln("PA0,0;") // Plot absolutely
+        hpgl.cmd("PU") // Raise Pen
+        hpgl.cmd("PA", Vector2.ZERO) // Plot absolutely
 
         composition.root.traverse { stage ->
             if (stage == Stage.Before) {
                 when (this) {
                     is ShapeNode -> {
-                        for (shape in this.shape.contours) {
+                        this.shape.contours.forEach { shape ->
                             val segments = shape.sampleLinear().segments
                             segments.forEachIndexed { i, segment ->
                                 if (i == 0) {
-                                    result.appendln("PU${segment.start.getCoords()};") // Go to shape start
-                                    result.appendln("PD${segment.end.getCoords()};")
+                                    hpgl.cmd("PU", segment.start) // Go to shape start
+                                    hpgl.cmd("PD", segment.end)
                                 } else {
-                                    result.appendln("PD${segment.start.getCoords()};") // PD coordinates for all other segments
-                                    result.appendln("PD${segment.end.getCoords()};") // PD coordinates for all other segments
+                                    hpgl.cmd("PD", segment.start) // PD coordinates for all other segments
+                                    hpgl.cmd("PD", segment.end) // PD coordinates for all other segments
                                 }
                             }
 
-                            result.appendln("PU;") // Done plotting
+                            hpgl.cmd("PU") // Done plotting
                         }
                     }
 
                     is SelectPen -> {
-                        result.appendln("SP${this.penNumber};")
+                        hpgl.cmd("SP", this.penNumber)
                     }
 
                     is VelocitySelect -> {
-                        result.appendln("VS${this.velocity};")
+                        hpgl.cmd("VS", this.velocity)
                     }
                 }
             }
         }
 
-        result.appendln("PA0,0;")
-        return result.toString()
+        hpgl.cmd("PA", Vector2.ZERO)
+        return hpgl.toString()
     }
 }
 
-private fun Vector2.getCoords(): String {
-    return "$x,$y"
-}
-
 private enum class Stage {
     Before,
     After
@@ -104,3 +104,14 @@ fun CompositionDrawer.velocitySelect(velocity: Double) {
     this.root.children.add(VelocitySelect(velocity))
 }
 
+private fun StringBuilder.cmd(cmd: String) = this.appendln("$cmd;")
+private fun StringBuilder.cmd(cmd: String, i: Int) = this.appendln("$cmd${i};")
+private fun StringBuilder.cmd(cmd: String, i: Double) = this.appendln("$cmd${i};")
+private fun StringBuilder.cmd(cmd: String, vararg vectors: Vector2) {
+    this.appendln(vectors.joinToString(prefix = cmd, postfix = ";") { it.coords })
+}
+
+private val Vector2.coords: String
+    get() {
+        return "$x,$y"
+    }