[SCM] WebKit Debian packaging branch, debian/experimental, updated. debian/1.3.8-1-1049-g2e11a8e

[commit-queue at webkit.org]

The following commit has been merged in the debian/experimental branch:
commit 613004480b36edae7c035a241d6329cb0743ee33
Author: commit-queue at webkit.org <commit-queue at webkit.org@268f45cc-cd09-0410-ab3c-d52691b4dbfc>
Date:   Wed Jan 5 01:14:53 2011 +0000

    2011-01-04  Cosmin Truta  <ctruta at chromium.org>
    
            Reviewed by Eric Seidel.
    
            [chromium] PNG compression settings optimized for speed
            https://bugs.webkit.org/show_bug.cgi?id=51719
    
            Although Z_HUFFMAN_ONLY is the fastest on hard-to-compress images,
            it is also the slowest, by a wide margin, on easy-to-compress images.
            Use a more balanced configuration, based on the libpng compression defaults,
            but with a faster compression level (3 instead of 6), and a faster filter
            ("sub" instead of "all").
    
            No change in behaviour, so no new tests.
    
            * platform/image-encoders/skia/PNGImageEncoder.cpp:
            (WebCore::PNGImageEncoder::encode):
    
    git-svn-id: http://svn.webkit.org/repository/webkit/trunk@75032 268f45cc-cd09-0410-ab3c-d52691b4dbfc

diff --git a/WebCore/ChangeLog b/WebCore/ChangeLog
index 5ece5a4..0cda95c 100644
--- a/WebCore/ChangeLog
+++ b/WebCore/ChangeLog
@@ -1,3 +1,21 @@
+2011-01-04  Cosmin Truta  <ctruta at chromium.org>
+
+        Reviewed by Eric Seidel.
+
+        [chromium] PNG compression settings optimized for speed
+        https://bugs.webkit.org/show_bug.cgi?id=51719
+
+        Although Z_HUFFMAN_ONLY is the fastest on hard-to-compress images,
+        it is also the slowest, by a wide margin, on easy-to-compress images.
+        Use a more balanced configuration, based on the libpng compression defaults,
+        but with a faster compression level (3 instead of 6), and a faster filter
+        ("sub" instead of "all").
+
+        No change in behaviour, so no new tests.
+
+        * platform/image-encoders/skia/PNGImageEncoder.cpp:
+        (WebCore::PNGImageEncoder::encode):
+
 2011-01-04  Chris Fleizach  <cfleizach at apple.com>
 
         Reviewed by Sam Weinig.
diff --git a/WebCore/platform/image-encoders/skia/PNGImageEncoder.cpp b/WebCore/platform/image-encoders/skia/PNGImageEncoder.cpp
index 265c14a..78f737e 100644
--- a/WebCore/platform/image-encoders/skia/PNGImageEncoder.cpp
+++ b/WebCore/platform/image-encoders/skia/PNGImageEncoder.cpp
@@ -83,8 +83,17 @@ bool PNGImageEncoder::encode(const SkBitmap& bitmap, Vector<unsigned char>* outp
         return false;
     }
 
-    png_set_compression_level(png, Z_BEST_SPEED);
-    png_set_compression_strategy(png, Z_HUFFMAN_ONLY);
+    // Optimize compression for speed.
+    // The parameters are the same as what libpng uses by default for RGB and RGBA images, except:
+    // - the zlib compression level is 3 instead of 6, to avoid the lazy Ziv-Lempel match searching;
+    // - the delta filter is 1 ("sub") instead of 5 ("all"), to reduce the filter computations.
+    // The zlib memory level (8) and strategy (Z_FILTERED) will be set inside libpng.
+    //
+    // Avoid the zlib strategies Z_HUFFMAN_ONLY or Z_RLE.
+    // Although they are the fastest for poorly-compressible images (e.g. photographs),
+    // they are very slow for highly-compressible images (e.g. text, drawings or business graphics).
+    png_set_compression_level(png, 3);
+    png_set_filter(png, PNG_FILTER_TYPE_BASE, PNG_FILTER_SUB);
 
     png_set_write_fn(png, output, writeOutput, 0);
     png_set_IHDR(png, info, imageSize.width(), imageSize.height(),

-- 
WebKit Debian packaging