[orx-camera] Re-add Camera2D (#275)

orx-camera/src/commonMain/kotlin/Camera2D.kt

@@ -0,0 +1,36 @@
+package org.openrndr.extra.camera
+
+import org.openrndr.Extension
+import org.openrndr.Program
+import org.openrndr.draw.Drawer
+import org.openrndr.math.Matrix44
+import org.openrndr.math.transforms.buildTransform
+
+/**
+ * The [Camera2D] extension enables:
+ * - **panning** the view by moving the mouse while a mouse button is pressed
+ * - **zooming** in and out by using the mouse wheel
+ *
+ * Usage: `extend(Camera2D())`
+ */
+class Camera2D : Extension {
+    override var enabled = true
+    var view = Matrix44.IDENTITY
+    override fun setup(program: Program) {
+        program.mouse.dragged.listen {
+            view = buildTransform { translate(it.dragDisplacement) } * view
+        }
+        program.mouse.scrolled.listen {
+            val scaleFactor = 1.0 - it.rotation.y * 0.03
+            view = buildTransform {
+                translate(it.position)
+                scale(scaleFactor)
+                translate(-it.position)
+            } * view
+        }
+    }
+
+    override fun beforeDraw(drawer: Drawer, program: Program) {
+        drawer.view = view
+    }
+}