Added orx-no-clear

orx-no-clear/README.md

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+# orx-no-clear
+
+A simple OPENRNDR Extension that provides the classical drawing-without-clearing-the-screen functionality that
+OPENRNDR does not support natively.
+
+#### Usage
+
+```
+class NoClearProgram: Program() {
+
+    override fun setup() {
+        backgroundColor = ColorRGBa.PINK
+        extend(NoClear())
+    }
+
+    override fun draw() {
+        drawer.circle(Math.cos(seconds) * width / 2.0 + width / 2.0, Math.sin(seconds * 0.24) * height / 2.0 + height / 2.0, 20.0)
+    }
+}
+
+```

orx-no-clear/src/main/kotlin/NoClear.kt

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+import org.openrndr.Extension
+import org.openrndr.Program
+import org.openrndr.color.ColorRGBa
+import org.openrndr.draw.Drawer
+import org.openrndr.draw.RenderTarget
+import org.openrndr.draw.isolated
+import org.openrndr.draw.renderTarget
+
+class NoClear : Extension {
+    override var enabled: Boolean = true
+    private var renderTarget: RenderTarget? = null
+
+
+    override fun beforeDraw(drawer: Drawer, program: Program) {
+        if (renderTarget == null || renderTarget?.width != program.width || renderTarget?.height != program.height) {
+            renderTarget?.let {
+                it.colorBuffer(0).destroy()
+                it.detachColorBuffers()
+                it.destroy()
+            }
+            renderTarget = renderTarget(program.width, program.height) {
+                colorBuffer()
+                depthBuffer()
+            }
+
+            renderTarget?.let {
+                drawer.withTarget(it) {
+                    background(program.backgroundColor ?: ColorRGBa.TRANSPARENT)
+                }
+            }
+        }
+        renderTarget?.bind()
+    }
+
+    override fun afterDraw(drawer: Drawer, program: Program) {
+        renderTarget?.unbind()
+
+        renderTarget?.let {
+            drawer.isolated {
+                drawer.ortho()
+                drawer.image(it.colorBuffer(0))
+            }
+        }
+    }
+}