Update libwebp to 0.4.0

third_party/libwebp/enc/config.c

Index: third_party/libwebp/enc/config.c
diff --git a/third_party/libwebp/enc/config.c b/third_party/libwebp/enc/config.c
index acf96b0f303ceb6bdf73fce39459af27e36fd3e9..af7f0b09e821dd9e2712817de9fc98bbd88f0edb 100644
--- a/third_party/libwebp/enc/config.c
+++ b/third_party/libwebp/enc/config.c
@@ -13,10 +13,6 @@
 
 #include "../webp/encode.h"
 
-#if defined(__cplusplus) || defined(c_plusplus)
-extern "C" {
-#endif
-
 //------------------------------------------------------------------------------
 // WebPConfig
 //------------------------------------------------------------------------------
@@ -33,7 +29,7 @@ int WebPConfigInitInternal(WebPConfig* config,
   config->target_PSNR = 0.;
   config->method = 4;
   config->sns_strength = 50;
-  config->filter_strength = 60;   // rather high filtering, helps w/ gradients.
+  config->filter_strength = 60;   // mid-filtering
   config->filter_sharpness = 0;
   config->filter_type = 1;        // default: strong (so U/V is filtered too)
   config->partitions = 0;
@@ -58,11 +54,13 @@ int WebPConfigInitInternal(WebPConfig* config,
       config->sns_strength = 80;
       config->filter_sharpness = 4;
       config->filter_strength = 35;
+      config->preprocessing &= ~2;   // no dithering
       break;
     case WEBP_PRESET_PHOTO:
       config->sns_strength = 80;
       config->filter_sharpness = 3;
       config->filter_strength = 30;
+      config->preprocessing |= 2;
       break;
     case WEBP_PRESET_DRAWING:
       config->sns_strength = 25;
@@ -72,10 +70,12 @@ int WebPConfigInitInternal(WebPConfig* config,
     case WEBP_PRESET_ICON:
       config->sns_strength = 0;
       config->filter_strength = 0;   // disable filtering to retain sharpness
+      config->preprocessing &= ~2;   // no dithering
       break;
     case WEBP_PRESET_TEXT:
       config->sns_strength = 0;
       config->filter_strength = 0;   // disable filtering to retain sharpness
+      config->preprocessing &= ~2;   // no dithering
       config->segments = 2;
       break;
     case WEBP_PRESET_DEFAULT:
@@ -111,7 +111,7 @@ int WebPValidateConfig(const WebPConfig* config) {
     return 0;
   if (config->show_compressed < 0 || config->show_compressed > 1)
     return 0;
-  if (config->preprocessing < 0 || config->preprocessing > 1)
+  if (config->preprocessing < 0 || config->preprocessing > 3)
     return 0;
   if (config->partitions < 0 || config->partitions > 3)
     return 0;
@@ -138,6 +138,3 @@ int WebPValidateConfig(const WebPConfig* config) {
 
 //------------------------------------------------------------------------------
 
-#if defined(__cplusplus) || defined(c_plusplus)
-}    // extern "C"
-#endif