From 2fe6c8805adb166cf4ccd9eff8df154f1d3fd7a6 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <kuba@niegowski.pl>
Date: Sun, 19 Aug 2012 23:36:53 +0200
Subject: [PATCH] bitblt

---
 lib/png.js | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/png.js b/lib/png.js
index 0d1e624..00cf3d1 100644
--- a/lib/png.js
+++ b/lib/png.js
@@ -92,3 +92,25 @@ PNG.prototype._metadata = function(width, height) {
     this.height = height;
     this.data = null;
 };
+
+PNG.prototype.bitblt = function(dst, sx, sy, w, h, dx, dy) {
+
+    var src = this;
+
+    if (sx > src.width || sy > src.height
+            || sx + w > src.width || sy + h > src.height)
+        throw new Error('bitblt reading outside image');
+    if (dy > dst.width || dy > dst.height
+            || dx + w > dst.width || dy + h > dst.height)
+        throw new Error('bitblt writing outside image');
+
+    for (var y = 0; y < h; y++) {
+        src.data.copy(dst.data,
+            ((dy + y) * dst.width + dx) << 2,
+            ((sy + y) * src.width + sx) << 2,
+            ((sy + y) * src.width + sx + w) << 2
+        );
+    }
+
+    return this;
+};