From 500fa6c3a934ac9d9f0a5c1ded5c00ad1709187f Mon Sep 17 00:00:00 2001
From: Derek Jones <derek.jones@ellislab.com>
Date: Mon, 12 May 2008 15:08:35 +0000
Subject: changed overlay_watermark() to check for an alpha value before
 applying the image to help support PNG-24s with alpha transparency

http://codeigniter.com/bug_tracker/bug/4506/
---
 system/libraries/Image_lib.php | 25 +++++++++++++++++++------
 user_guide/changelog.html      |  3 ++-
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/system/libraries/Image_lib.php b/system/libraries/Image_lib.php
index 0750b6454..4017afb13 100644
--- a/system/libraries/Image_lib.php
+++ b/system/libraries/Image_lib.php
@@ -943,10 +943,23 @@ class CI_Image_lib {
 		{
 			@imagealphablending($src_img, TRUE);
 		} 		
-
-		// Set RGB values for text and shadow		
-		imagecolortransparent($wm_img, imagecolorat($wm_img, $this->wm_x_transp, $this->wm_y_transp));
-		imagecopymerge($src_img, $wm_img, $x_axis, $y_axis, 0, 0, $wm_width, $wm_height, $this->wm_opacity);
+		
+		// Set RGB values for text and shadow
+		$rgba = imagecolorat($wm_img, $this->wm_x_transp, $this->wm_y_transp);
+		$alpha = ($rgba & 0x7F000000) >> 24;
+		
+		// make a best guess as to whether we're dealing with an image with alpha transparency or no/binary transparency
+		if ($alpha > 0)
+		{
+			// copy the image directly, the image's alpha transparency being the sole determinant of blending
+			imagecopy($src_img, $wm_img, $x_axis, $y_axis, 0, 0, $wm_width, $wm_height);
+		}
+		else
+		{
+			// set our RGB value from above to be transparent and merge the images with the specified opacity
+			imagecolortransparent($wm_img, imagecolorat($wm_img, $this->wm_x_transp, $this->wm_y_transp));
+			imagecopymerge($src_img, $wm_img, $x_axis, $y_axis, 0, 0, $wm_width, $wm_height, $this->wm_opacity);			
+		}
 				
 		//  Output the image
 		if ($this->dynamic_output == TRUE)
@@ -1533,6 +1546,6 @@ class CI_Image_lib {
 
 }
 // END Image_lib Class
-
-/* End of file Image_lib.php */
+
+/* End of file Image_lib.php */
 /* Location: ./system/libraries/Image_lib.php */
\ No newline at end of file
diff --git a/user_guide/changelog.html b/user_guide/changelog.html
index c5231655c..43905db3f 100644
--- a/user_guide/changelog.html
+++ b/user_guide/changelog.html
@@ -139,7 +139,8 @@ SVN Commit: not currently released</p>
 	<li>Fixed a bug in the table library that could cause identically constructed rows to be dropped (#3459).</li>
 	<li>Fixed a bug (#4206) in the Directory Helper where the directory resource was not being closed, and minor improvements.</li>
 	<li>Fixed a bug where SMTP emails were not having dot transformation performed on lines that begin with a dot.</li>
-	<li>Fixed a bug in display_error() in the DB driver that was instantiating new Language and Exception objects, and not using the error heading.</li> 
+	<li>Fixed a bug in display_error() in the DB driver that was instantiating new Language and Exception objects, and not using the error heading.</li>
+	<li>Fixed a bug (#4506) with overlay_watermark() in the Image library preventing support for PNG-24s with alpha transparency</li>
 </ul>
 
 <h2>Version 1.6.1</h2>
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