[gfx] Add a utility to calculate visible margins of an image.

ui/gfx/image/image_util.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/image/image_util.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/codec/jpeg_codec.h"
 #include "ui/gfx/image/image.h"
 #include "ui/gfx/image/image_skia.h"
 
 namespace gfx {
 
 // The iOS implementations of the JPEG functions are in image_util_ios.mm.
 #if !defined(OS_IOS)
 Image ImageFrom1xJPEGEncodedData(const unsigned char* input,
                                  size_t input_size) {
   scoped_ptr<SkBitmap> bitmap(gfx::JPEGCodec::Decode(input, input_size));
   if (bitmap.get())
     return Image::CreateFrom1xBitmap(*bitmap);
 
   return Image();
 }
 
 bool JPEG1xEncodedDataFromImage(const Image& image, int quality,
-                              std::vector<unsigned char>* dst) {
+                                std::vector<unsigned char>* dst) {
   const gfx::ImageSkiaRep& image_skia_rep =
       image.AsImageSkia().GetRepresentation(1.0f);
   if (image_skia_rep.scale() != 1.0f)
     return false;
 
   const SkBitmap& bitmap = image_skia_rep.sk_bitmap();
   SkAutoLockPixels bitmap_lock(bitmap);
 
   if (!bitmap.readyToDraw())
     return false;
 
   return gfx::JPEGCodec::Encode(
           reinterpret_cast<unsigned char*>(bitmap.getAddr32(0, 0)),
           gfx::JPEGCodec::FORMAT_SkBitmap, bitmap.width(),
           bitmap.height(),
           static_cast<int>(bitmap.rowBytes()), quality,
           dst);
 }
 #endif  // !defined(OS_IOS)
 
+bool VisibleMargins(const ImageSkia& image, int* leading, int* trailing) {
+  *leading = 0;
+  *trailing = std::max(1, image.width()) - 1;
+  if (!image.HasRepresentation(1.0))
+    return false;
+
+  const ImageSkiaRep& rep = image.GetRepresentation(1.0);
+  if (rep.is_null())
+    return false;
+
+  const SkBitmap& bitmap = rep.sk_bitmap();
+  if (bitmap.isNull() || bitmap.width() == 0)
+    return false;
+
+  if (bitmap.isOpaque())
+    return true;
+
+  SkAutoLockPixels l(bitmap);
+  int innerMin = bitmap.width();

[Robert Sesek, 2014/01/30 20:41:38]

naming: Use under_scores, not camelCase. Here and on line 78.

[Greg Billock, 2014/01/30 23:39:19]

Done.

+  for (int x = 0; x < bitmap.width(); ++x) {
+    for (int y = 0; y < bitmap.height(); ++y) {
+      if (SkColorGetA(bitmap.getColor(x, y)) > 12) {
+        innerMin = x;
+        break;
+      }
+    }
+    if (innerMin < bitmap.width())
+      break;
+  }
+
+  int innerMax = -1;
+  for (int x = bitmap.width() - 1; x > innerMin; --x) {
+    for (int y = 0; y < bitmap.height(); ++y) {
+      if (SkColorGetA(bitmap.getColor(x, y)) > 12) {
+        innerMax = x;
+        break;
+      }
+    }
+    if (innerMax > -1)
+      break;
+  }
+
+  if (innerMin == bitmap.width()) {
+    *leading = bitmap.width()/2;
+    *trailing = bitmap.width()/2 + 1;
+    return true;
+  }
+
+  *leading = innerMin;
+  *trailing = innerMax;
+  return true;
 }
+
+}  // namespace gfx