Add AxisHelper to orx-camera

* Rename Debug3D to GridHelper

orx-camera/src/main/kotlin/GridHelper.kt

@@ -0,0 +1,56 @@
+package org.openrndr.extras.camera
+
+import org.openrndr.Extension
+import org.openrndr.Program
+import org.openrndr.color.ColorRGBa
+import org.openrndr.draw.*
+import org.openrndr.math.Vector3
+
+@Suppress("unused")
+class GridHelper(val size: Int = 10, val divisions: Int = 10) : Extension {
+    override var enabled: Boolean = true
+    private val step = size / divisions.toDouble()
+
+    private val grid = vertexBuffer(
+            vertexFormat {
+                position(3)
+            }
+            , 4 * (size * divisions + 1)).apply {
+        put {
+            val halfSize = size / 2.0
+            var k = -halfSize
+
+            for(i in 0 until divisions + 1) {
+                write(Vector3(-halfSize, 0.0, k))
+                write(Vector3(halfSize, 0.0, k))
+
+                write(Vector3(k, 0.0, -halfSize))
+                write(Vector3(k, 0.0, halfSize))
+
+                k += step
+            }
+        }
+    }
+
+    override fun beforeDraw(drawer: Drawer, program: Program) {
+        draw(drawer)
+    }
+
+    fun draw(drawer: Drawer) {
+        drawer.isolated {
+            drawer.fill = ColorRGBa.WHITE
+            drawer.stroke = ColorRGBa.WHITE
+            drawer.vertexBuffer(grid, DrawPrimitive.LINES)
+
+            // Axis cross
+            drawer.stroke = ColorRGBa.RED
+            drawer.lineSegment(Vector3.ZERO, Vector3(step, 0.0, 0.0))
+
+            drawer.stroke = ColorRGBa.GREEN
+            drawer.lineSegment(Vector3.ZERO, Vector3(0.0, step, 0.0))
+
+            drawer.stroke = ColorRGBa.BLUE
+            drawer.lineSegment(Vector3.ZERO, Vector3(0.0, 0.0, step))
+        }
+    }
+}