PostProcessor working: nested FBO won't work, use FrameBufferManager

src/net/torvald/terrarum/FrameBufferManager.java

@@ -0,0 +1,30 @@
+package net.torvald.terrarum;
+
+import com.badlogic.gdx.graphics.glutils.FrameBuffer;
+
+import java.util.Stack;
+
+/**
+ * Nested FBOs are just not a thing in GL!
+ *
+ * Created by minjaesong on 2018-07-03.
+ *
+ * @link https://stackoverflow.com/questions/25471727/libgdx-nested-framebuffer
+ */
+public class FrameBufferManager {
+    private static Stack<FrameBuffer> stack = new Stack<FrameBuffer>();
+
+    public static void begin(FrameBuffer buffer) {
+        if (!stack.isEmpty()) {
+            stack.peek().end();
+        }
+        stack.push(buffer).begin();
+    }
+
+    public static void end() {
+        stack.pop().end();
+        if (!stack.isEmpty()) {
+            stack.peek().begin();
+        }
+    }
+}