Desktop chrome tab capture-chooseDesktopMedia()

chrome/browser/media/desktop_media_list.h

 // Copyright 2013 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.
 
 #ifndef CHROME_BROWSER_MEDIA_DESKTOP_MEDIA_LIST_H_
 #define CHROME_BROWSER_MEDIA_DESKTOP_MEDIA_LIST_H_
 
 #include "base/basictypes.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "content/public/browser/desktop_media_id.h"
+#include "ui/gfx/image/image.h"
 #include "ui/gfx/image/image_skia.h"
 
 class DesktopMediaListObserver;
 
 // DesktopMediaList provides the list of desktop media source (screens, windows,
 // tabs), and their thumbnails, to the desktop media picker dialog. It
 // transparently updates the list in the background, and notifies the desktop
 // media picker when something changes.
 class DesktopMediaList {
  public:
+  enum SourceTypes { SCREENS = 1, WINDOWS = 2, TABS = 4 };
   // Struct used to represent each entry in the list.
   struct Source {
     // Id of the source.
     content::DesktopMediaID id;
 
     // Name of the source that should be shown to the user.
     base::string16 name;
 
     // The thumbnail for the source.
     gfx::ImageSkia thumbnail;
@@ skipping 17 matching lines @@
 
   // Starts updating the model. The model is initially empty, so OnSourceAdded()
   // notifications will be generated for each existing source as it is
   // enumerated. After the initial enumeration the model will be refreshed based
   // on the update period, and notifications generated only for changes in the
   // model.
   virtual void StartUpdating(DesktopMediaListObserver* observer) = 0;
 
   virtual int GetSourceCount() const = 0;
   virtual const Source& GetSource(int index) const = 0;
+
+ protected:
+  // Create a image with an enlarged favicon on its center and black boundary.
+  // If fails, an empty image will return.
+  // The function is used to create a thumbnail for chrome tab preview.
+  static gfx::ImageSkia CreateImageEncloseFavicon(gfx::Size size,

[qiangchen, 2015/12/07 22:45:56]

Better to separate the definition from declaration, as this function is large.

[GeorgeZ, 2015/12/09 19:36:37]

Done.

+                                                  gfx::Image& favicon) {
+    // Enlarge scale for favicon.
+    int scale = 3;

[qiangchen, 2015/12/07 22:45:56]

const?

[GeorgeZ, 2015/12/09 19:36:37]

Done.

+    // Thickness of image boundary.
+    int thick = 5;

[qiangchen, 2015/12/07 22:45:56]

const?

[GeorgeZ, 2015/12/09 19:36:37]

Done.

+
+    // Sanity check. If failed, return a empty image.
+    if (size.width() < favicon.Width() * scale ||
+        size.height() < favicon.Height() * scale)
+      return gfx::ImageSkia();
+
+    // Create a SkBitmap for faviocn.
+    SkBitmap icon = favicon.AsBitmap();
+
+    // Create a bitmap.
+    SkBitmap result;
+    result.allocN32Pixels(size.width(), size.height(), true);
+
+    // Two SkBitmaps' color type need match to merge.
+    if (icon.colorType() != result.colorType())
+      return gfx::ImageSkia();
+
+    result.lockPixels();
+    uint8* pixels_data = reinterpret_cast<uint8*>(result.getPixels());
+
+    // Set background.
+    int span = result.rowBytes();
+    int bpp = result.bytesPerPixel();

[qiangchen, 2015/12/07 22:45:56]

Again my question, the follow code seems to assume bpp = 4. 
Is that always true?

[GeorgeZ, 2015/12/09 19:36:37]

 result.allocN32Pixels() guarantees result image's bpp=4;

(icon.colorType() != result.colorType())
  return gfx::ImageSkia();

guarantees result image's bpp == icon image's bpp

+    for (int y = 0; y < result.height(); ++y) {
+      for (int x = 0; x < result.width(); ++x) {
+        if (y < thick || y >= result.height() - thick || x < thick ||
+            x >= result.width() - thick) {
+          pixels_data[span * y + x * bpp] = 0;
+          pixels_data[span * y + x * bpp + 1] = 0;
+          pixels_data[span * y + x * bpp + 2] = 0;
+        } else {
+          pixels_data[span * y + x * bpp] = 0xff;
+          pixels_data[span * y + x * bpp + 1] = 0xff;
+          pixels_data[span * y + x * bpp + 2] = 0xff;
+        }
+        pixels_data[span * y + x * bpp + 3] = 0xff;
+      }
+    }
+
+    // Copy enlarged favicon into center of result image.
+    icon.lockPixels();
+    uint8* icon_data = reinterpret_cast<uint8*>(icon.getPixels());
+
+    int icon_span = icon.rowBytes();
+    int icon_bpp = icon.bytesPerPixel();
+    int offsety = (result.height() - icon.height() * scale) / 2;
+    int offsetx = (result.width() - icon.width() * scale) / 2;
+    for (int y = 0; y < icon.height() * scale; ++y) {
+      for (int x = 0; x < icon.width() * scale; ++x) {
+        pixels_data[span * (y + offsety) + (x + offsetx) * bpp] =
+            icon_data[icon_span * (y / scale) + (x / scale) * icon_bpp];
+        pixels_data[span * (y + offsety) + (x + offsetx) * bpp + 1] =
+            icon_data[icon_span * (y / scale) + (x / scale) * icon_bpp + 1];
+        pixels_data[span * (y + offsety) + (x + offsetx) * bpp + 2] =
+            icon_data[icon_span * (y / scale) + (x / scale) * icon_bpp + 2];
+      }
+    }
+    icon.unlockPixels();
+    result.unlockPixels();
+
+    // Create a skia image.
+    return gfx::ImageSkia::CreateFrom1xBitmap(result);
+  }
 };
 
 #endif  // CHROME_BROWSER_MEDIA_DESKTOP_MEDIA_LIST_H_