a WebP encoder

converts PNG & JPEG to WebP

This is an experimental early version, with lot of room
of later optimizations in both speed and quality.

Compile with the usual `./configure && make`
Command line example is examples/cwebp

Usage:

   cwebp [options] -q quality input.png -o output.webp

where 'quality' is between 0 (poor) to 100 (very good).
Typical value is around 80.

More encoding options with 'cwebp -longhelp'

Change-Id: I577a94f6f622a0c44bdfa9daf1086ace89d45539

src/enc/config.c

@@ -0,0 +1,107 @@
+// Copyright 2011 Google Inc.
+//
+// This code is licensed under the same terms as WebM:
+//  Software License Agreement:  http://www.webmproject.org/license/software/
+//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
+// -----------------------------------------------------------------------------
+//
+// Coding tools configuration
+//
+// Author: Skal (pascal.massimino@gmail.com)
+
+#include <assert.h>
+#include "webp/encode.h"
+
+//-----------------------------------------------------------------------------
+// WebPConfig
+//-----------------------------------------------------------------------------
+
+int WebPConfigInitInternal(WebPConfig* const config,
+                           WebPPreset preset, float quality, int version) {
+  if (version != WEBP_ENCODER_ABI_VERSION) {
+    return 0;   // caller/system version mismatch!
+  }
+  if (config == NULL) return 0;
+
+  config->quality = quality;
+  config->target_size = 0;
+  config->target_PSNR = 0.;
+  config->method = 4;
+  config->sns_strength = 50;
+  config->filter_strength = 20;   // default: light filtering
+  config->filter_sharpness = 0;
+  config->filter_type = 0;        // default: simple
+  config->partitions = 0;
+  config->segments = 4;
+  config->pass = 1;
+  config->show_compressed = 0;
+  config->preprocessing = 0;
+  config->autofilter = 0;
+
+  // TODO(skal): tune.
+  switch (preset) {
+    case WEBP_PRESET_PICTURE:
+      config->sns_strength = 80;
+      config->filter_sharpness = 4;
+      config->filter_strength = 35;
+      break;
+    case WEBP_PRESET_PHOTO:
+      config->sns_strength = 80;
+      config->filter_sharpness = 3;
+      config->filter_strength = 30;
+      break;
+    case WEBP_PRESET_DRAWING:
+      config->sns_strength = 25;
+      config->filter_sharpness = 6;
+      config->filter_strength = 10;
+      break;
+    case WEBP_PRESET_ICON:
+      config->sns_strength = 0;
+      config->filter_strength = 0;   // disable filtering to retain sharpness
+      break;
+    case WEBP_PRESET_TEXT:
+      config->sns_strength = 0;
+      config->filter_strength = 0;   // disable filtering to retain sharpness
+      config->segments = 2;
+      break;
+    case WEBP_PRESET_DEFAULT:
+    default:
+      break;
+  }
+  return WebPValidateConfig(config);
+}
+
+int WebPValidateConfig(const WebPConfig* const config) {
+  if (config == NULL) return 0;
+  if (config->quality < 0 || config->quality > 100)
+    return 0;
+  if (config->target_size < 0)
+    return 0;
+  if (config->target_PSNR < 0)
+    return 0;
+  if (config->method < 0 || config->method > 6)
+    return 0;
+  if (config->segments < 1 || config->segments > 4)
+    return 0;
+  if (config->sns_strength < 0 || config->sns_strength > 100)
+    return 0;
+  if (config->filter_strength < 0 || config->filter_strength > 100)
+    return 0;
+  if (config->filter_sharpness < 0 || config->filter_sharpness > 7)
+    return 0;
+  if (config->filter_type < 0 || config->filter_type > 1)
+    return 0;
+  if (config->autofilter < 0 || config->autofilter > 1)
+    return 0;
+  if (config->pass < 1 || config->pass > 10)
+    return 0;
+  if (config->show_compressed < 0 || config->show_compressed > 1)
+    return 0;
+  if (config->preprocessing < 0 || config->preprocessing > 1)
+    return 0;
+  if (config->partitions < 0 || config->partitions > 3)
+    return 0;
+  return 1;
+}
+
+//-----------------------------------------------------------------------------