[orx-shapes] Add demos, tweak comments

orx-shapes/src/jvmDemo/kotlin/alphashape/DemoAlphaShape02.kt

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+package alphashape
+
+import org.openrndr.application
+import org.openrndr.color.ColorRGBa
+import org.openrndr.extra.noise.shapes.uniform
+import org.openrndr.extra.shapes.alphashape.AlphaShape
+import org.openrndr.math.Vector2
+import kotlin.random.Random
+
+/**
+ * Demonstrates the use of [AlphaShape] to create ten
+ * [org.openrndr.shape.ShapeContour] instances out of a collection of random [Vector2] points.
+ *
+ * The same points are used for each contour, but an increased alpha parameter
+ * is passed to the AlphaShape algorithm. Higher values return more convex shapes
+ * = shapes with a larger surface.
+ *
+ * The list of shapes is reversed to draw the smaller contours on top, otherwise only
+ * the last one would be visible.
+ *
+ * An instance of [Random] with a fixed seed is used to ensure the resulting
+ * random shape is always the same.
+ */
+fun main() = application {
+    program {
+        val rand = Random(242)
+        val points = List(40) {
+            drawer.bounds.uniform(rand)
+        }
+        val alphaShape = AlphaShape(points)
+        val minAlpha = alphaShape.determineContourAlpha()
+
+        val contours = List(10) {
+            alphaShape.createContour(minAlpha + it * it * it)
+        }.reversed()
+        extend {
+            drawer.stroke = null
+            contours.forEachIndexed { index, contour ->
+                drawer.fill = ColorRGBa.PINK.shade(0.5 + index * 0.07)
+                drawer.contour(contour)
+            }
+
+            drawer.fill = ColorRGBa.WHITE
+            drawer.circles(points, 4.0)
+        }
+    }
+}