From c4699a46daeffee2165626850a0757740e42fbab Mon Sep 17 00:00:00 2001
From: sbarman <sbarman@L3CWZ5T.(none)>
Date: Sun, 25 Sep 2011 16:27:06 -0700
Subject: [PATCH] fix bugs with predictors, png predictor type 0 and 5 (ie noop
 and paeth)

---
 pdf.js | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/pdf.js b/pdf.js
index 224becdf1..24066d7bf 100644
--- a/pdf.js
+++ b/pdf.js
@@ -714,7 +714,6 @@ var PredictorStream = (function() {
     var columns = this.columns = params.get('Columns') || 1;
 
     this.pixBytes = (colors * bits + 7) >> 3;
-    // add an extra pixByte to represent the pixel left of column 0
     this.rowBytes = (columns * colors * bits + 7) >> 3;
 
     DecodeStream.call(this);
@@ -796,10 +795,12 @@ var PredictorStream = (function() {
     var currentRow = buffer.subarray(bufferLength, bufferLength + rowBytes);
     var prevRow = buffer.subarray(bufferLength - rowBytes, bufferLength);
     if (prevRow.length == 0)
-      prevRow = currentRow;
+      prevRow = new Uint8Array(rowBytes);
 
     switch (predictor) {
       case 0:
+        for (var i = 0; i < rowBytes; ++i)
+          currentRow[i] = rawBytes[i];
         break;
       case 1:
         for (var i = 0; i < pixBytes; ++i)
@@ -822,8 +823,11 @@ var PredictorStream = (function() {
       case 4:
         // we need to save the up left pixels values. the simplest way
         // is to create a new buffer
-        for (var i = 0; i < pixBytes; ++i)
-          currentRow[i] = rawBytes[i];
+        for (var i = 0; i < pixBytes; ++i) {
+          var up = prevRow[i];
+          var c = rawBytes[i];
+          currentRow[i] = up + c;
+        }
         for (; i < rowBytes; ++i) {
           var up = prevRow[i];
           var upLeft = prevRow[i - pixBytes];