From 1d05e3d265a03b00f621b5d1769196dd3e74a397 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sat, 18 Jul 2015 15:18:57 -0700
Subject: [PATCH] optimize tng for disposeOp=2.

---
 vendor/tng.js | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/vendor/tng.js b/vendor/tng.js
index 99ff65f..731ef6c 100644
--- a/vendor/tng.js
+++ b/vendor/tng.js
@@ -932,14 +932,18 @@ PNG.prototype.renderFrame = function(bmp, frame, i) {
     }
   }
 
-  this._lastBmp = [];
-  for (y = 0; y < frame.fctl.height; y++) {
-    line = [];
-    for (x = 0; x < frame.fctl.width; x++) {
-      p = this._curBmp[yo + y][xo + x];
-      line.push({ r: p.r, g: p.g, b: p.b, a: p.a });
+  if (frame.fctl.disposeOp === 2) {
+    this._lastBmp = [];
+    for (y = 0; y < frame.fctl.height; y++) {
+      line = [];
+      for (x = 0; x < frame.fctl.width; x++) {
+        p = this._curBmp[yo + y][xo + x];
+        line.push({ r: p.r, g: p.g, b: p.b, a: p.a });
+      }
+      this._lastBmp.push(line);
     }
-    this._lastBmp.push(line);
+  } else {
+    this._lastBmp = null;
   }
 
   for (y = 0; y < frame.fctl.height; y++) {