Removed an extra space that was added between commands.

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/TemplateProgram.kt

@@ -1,13 +1,11 @@
-import com.martianwabbit.HPGL
-import com.martianwabbit.logger
+
+import com.martianwabbit.saveToHPGL
+import com.martianwabbit.selectPen
 import org.openrndr.application
 import org.openrndr.color.ColorRGBa
 import org.openrndr.math.Vector2
 import org.openrndr.shape.CompositionDrawer
 import java.io.File
-import com.martianwabbit.saveToHPGL
-import org.openrndr.Configuration
-import org.openrndr.Program
 
 fun main() = application {
     configure {
@@ -18,10 +16,12 @@ fun main() = application {
     program {
         extend {
             val c = CompositionDrawer()
-            c.circle(Vector2(20.0, 20.0), 12.0)
-
-            c.composition.saveToHPGL(File("output.plt"))
+            c.selectPen(1)
+            c.circle(Vector2(40.0, 40.0), 30.0)
+            c.rectangle(75.0, 60.0, 80.0, 200.0)
+            c.lineSegment(Vector2(0.0, 0.0), Vector2(200.0, 200.0))
 
+            c.composition.saveToHPGL(File("output.plt"), this.width, this.height)
 
             this.application.exit()
             drawer.background(ColorRGBa.WHITE)

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

@@ -3,42 +3,69 @@ package com.martianwabbit
 import org.openrndr.math.Vector2
 import org.openrndr.shape.*
 import java.io.File
-import java.util.logging.Logger
-import kotlin.math.pow
-import kotlin.math.sqrt
 
-val logger = Logger.getLogger("")
-
-fun Composition.saveToHPGL(file: File) {
-    HPGL().generateFromComposition(this)
+fun Composition.saveToHPGL(file: File, width: Int = 0, height: Int = 0) {
+    val plot = HPGL(width = width, height = height).generateFromComposition(this)
+    file.writeText(plot)
 }
 
-class HPGL(pageSize: PageSize = PageSize.A4) {
-    fun generateFromComposition(composition: Composition) {
-        composition.root.traverse { shape ->
-            if (shape == Stage.Before) {
-                if (this is ShapeNode) {
+class HPGL(
+    private val p1: Vector2 = Vector2.ZERO,
+    private val p2: Vector2 = Vector2.ZERO,
+    private val width: Int = 0,
+    private val height: Int = 0
+) {
+    fun generateFromComposition(composition: Composition): String {
+        val hpgl = StringBuilder()
+
+        hpgl.cmd("IN")
+
+        // Setup plotter coordinates
+        if (p1 != Vector2.ZERO || p2 != Vector2.ZERO) {
+            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) {
+            hpgl.cmd("SC")
+        } else {
+            hpgl.cmd("SC", Vector2(.0, width.toDouble()), Vector2(.0, height.toDouble()))
+        }
+
+        hpgl.cmd("PU") // Raise Pen
+        hpgl.cmd("PA", Vector2.ZERO) // Plot absolutely
+
+        composition.root.traverse { stage ->
+            if (stage == Stage.Before) {
+                when (this) {
+                    is ShapeNode -> {
                         this.shape.contours.forEach { shape ->
-                        val i = shape.sampleEquidistant(200)
-                        val rr = StringBuilder()
-                        for (v in i.segments) {
-                            rr.appendln("${v.start.x}, ${v.start.y}")
-                        }
-                        calculateSpline(shape.segments)
+                            val segments = shape.sampleLinear().segments
+                            segments.forEachIndexed { i, segment ->
+                                if (i == 0) {
+                                    hpgl.cmd("PU", segment.start) // Go to shape start
+                                    hpgl.cmd("PD", segment.end)
+                                } else {
+                                    hpgl.cmd("PD", segment.start, segment.end) // PD coordinates for all other segments
                                 }
                             }
+
+                            hpgl.cmd("PU") // Done plotting
                         }
                     }
+
+                    is SelectPen -> hpgl.cmd("SP", this.penNumber)
+                    is VelocitySelect -> hpgl.cmd("VS", this.velocity)
+                }
             }
         }
 
-private fun Vector2.distanceTo(point: Vector2): Double {
-    return sqrt((point.x - this.x).pow(2.0) + (point.y - this.y).pow(2.0))
+        hpgl.cmd("PA", Vector2.ZERO)
+        return hpgl.toString()
     }
-
-enum class PageSize {
-    A4,
-    A3
 }
 
 private enum class Stage {
@@ -49,51 +76,37 @@ private enum class Stage {
 private fun CompositionNode.traverse(cb: CompositionNode.(stage: Stage) -> Unit) {
     this.cb(Stage.Before)
 
-    if (this is GroupNode) {
+    if (this is GroupNode && this.children.size > 0) {
         this.children.forEach { it.traverse(cb) }
     }
+
+    this.cb(Stage.After)
 }
 
-// These default values correspond to a centripetal Catmull-Rom spline
-private fun calculateSpline(segments: List<Segment>, resolution: Int = 100, alpha: Double = .5, tension: Double = .0) {
-    val result = mutableListOf<Vector2>()
-    segments.forEach {
-        val points = mutableListOf<Vector2>()
-        points.add(it.start)
-        points.addAll(it.control)
-        points.add(it.end)
-
-        when(points.size) {
-            4 -> { // Catmull-Rom
-                val t0 = 0.0
-                val t1 = t0 + points[0].distanceTo(points[1]).pow(alpha)
-                val t2 = t1 + points[1].distanceTo(points[2]).pow(alpha)
-                val t3 = t2 + points[2].distanceTo(points[3]).pow(alpha)
-
-                val p0 = points[0]
-                val p1 = points[1]
-                val p2 = points[2]
-                val p3 = points[3]
-
-                val m1 = ((p1 - p0) / (t1 - t0) - (p2 - p0) / (t2 - t0) + (p2 - p1) / (t2 - t1)) * (1.0 - tension) * (t2 - t1)
-                val m2 = ((p2 - p1) / (t2 - t1) - (p3 - p1) / (t3 - t1) + (p3 - p2) / (t3 - t2)) * (1.0 - tension) * (t2 - t1)
-
-                val a = (p1 - p2) + m1 + m2 * 2.0
-                val b = ((p1 - p2) * -3.0) - m1 - m1 - m2
-
-                for (i in 0..100 step 10) {
-                    val t = (i / 100).toDouble()
-                    val r = a * t.pow(3) + b * t.pow(2) + m1 * t.pow(1) + p1
-                    result.add(r)
-                }
-            }
-        }
+private val Vector2.coords: String
+    get() {
+        return "$x,$y"
     }
 
-    val rr = StringBuilder()
-    for (v in result) {
-        rr.appendln("${v.x}, ${v.y}")
+
+// HPGL Custom Instructions
+private class SelectPen(val penNumber: Int) : GroupNode()
+
+fun CompositionDrawer.selectPen(pen: Int) {
+    require(pen >= 0) { "The pen can only be 0 or greater." }
+    this.root.children.add(SelectPen(pen))
 }
-    val a = Vector2(0.0, 10.0).distanceTo(Vector2(13.0, 12.0))
-    logger.info("done")
+
+private class VelocitySelect(val velocity: Double) : GroupNode()
+
+fun CompositionDrawer.velocitySelect(velocity: Double) {
+    require(velocity in 0.0..127.9999) { "Invalid velocity value. The velocity should be a value between 0 and 127.9999" }
+    this.root.children.add(VelocitySelect(velocity))
 }
+
+// StringBuilder Extensions
+private fun StringBuilder.cmd(cmd: String) = this.appendln("$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(separator = ",", prefix = cmd, postfix = ";") { it.coords })