[orx-composition] Add test and demo for PR#360

orx-composition/src/commonTest/kotlin/TestComposition.kt

@@ -1,7 +1,14 @@
 package org.openrndr.extra.composition
 
+import org.openrndr.math.Vector2
+import org.openrndr.shape.Circle
+import org.openrndr.shape.LineSegment
+import org.openrndr.shape.Rectangle
 import org.openrndr.shape.Shape
-import kotlin.test.*
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
 
 class TestComposition {
     val composition = let { _ ->
@@ -35,4 +42,46 @@ class TestComposition {
         assertNull(composition.findImage("outer"))
         assertNull(composition.findImage("shape"))
     }
+}
+
+class TestCompositionIntersections {
+    val bounds = Rectangle(Vector2.ZERO, 640.0, 480.0)
+    val outline = Shape(
+        listOf(
+            Circle(bounds.center, 70.0).contour.reversed,
+            Circle(bounds.center, 100.0).contour,
+        )
+    )
+
+    val radius = outline.bounds.dimensions.length / 2
+    val off = outline.bounds.center
+    val num = radius.toInt()
+
+    @Test
+    fun `use a shape as a mask for line segments`() {
+        // Make sure intersections do not fail randomly, which was fixed in
+        // https://github.com/openrndr/orx/commit/e8f50b3dd153ed82de121e9017cf42f6ea95ac8e
+        val svg = List(100) {
+            drawComposition {
+                lineSegments(List(num) { segNum ->
+                    val yNorm = (segNum / (num - 1.0))
+                    val x = ((segNum % 2) * 2.0 - 1.0) * radius
+                    val y = (yNorm * 2.0 - 1.0) * radius
+                    val start = Vector2(-x, y) + off
+                    val end = Vector2(x, y) + off
+                    LineSegment(start, end)
+                })
+                clipMode = ClipMode.INTERSECT
+                shape(outline)
+            }
+        }
+
+        val shapes = svg[50].findShapes()
+        val dimensions = svg[50].bounds.dimensions
+
+        assertTrue(shapes.isNotEmpty())
+        assertTrue(shapes.first().shape.contours.isNotEmpty())
+        assertTrue(dimensions.x > 0.0)
+        assertTrue(dimensions.y > 0.0)
+    }
 }