Change Aura desktop background behavior.

ash/desktop_background/desktop_background_view.cc

Index: ash/desktop_background/desktop_background_view.cc
diff --git a/ash/desktop_background/desktop_background_view.cc b/ash/desktop_background/desktop_background_view.cc
index 44526cb89a1adee344acc78023614709d848d2c7..79470f0dbddb8f9ddf40cab326ee3758554f3604 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -4,6 +4,8 @@
 
 #include "ash/desktop_background/desktop_background_view.h"
 
+#include <limits>
+
 #include "ash/ash_export.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ -18,6 +20,11 @@
 namespace ash {
 namespace internal {
 
+// For our scaling ratios we need to round positive numbers.
+static int RoundPositive(double x) {
+  return static_cast<int>(floor(x + 0.5));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopBackgroundView, public:
 
@@ -34,10 +41,43 @@ DesktopBackgroundView::~DesktopBackgroundView() {
 // DesktopBackgroundView, views::View overrides:
 
 void DesktopBackgroundView::OnPaint(gfx::Canvas* canvas) {
-  canvas->DrawBitmapInt(wallpaper_,
-      0, 0, wallpaper_.width(), wallpaper_.height(),
-      0, 0, width(), height(),
-      true);
+  // Scale the image while maintaining the aspect ratio, cropping as
+  // necessary to fill the background. Ideally the image should be larger
+  // than the largest display supported, if not we will center it rather than
+  // streching to avoid upsampling artifacts (Note that we could tile too, but
+  // decided not to do this at the moment).
+  gfx::Rect wallpaper_rect(0, 0, wallpaper_.width(), wallpaper_.height());
+  if (wallpaper_.width() > width() && wallpaper_.height() > height()) {
+    // The dimension with the smallest ratio must be cropped, the other one
+    // is preserved. Both are set in gfx::Size cropped_size.
+    double horizontal_ratio = static_cast<double>(width()) /
+        static_cast<double>(wallpaper_.width());
+    double vertical_ratio = static_cast<double>(height()) /
+        static_cast<double>(wallpaper_.height());
+
+    gfx::Size cropped_size;
+    if (vertical_ratio > horizontal_ratio) {
+      cropped_size = gfx::Size(
+          RoundPositive(static_cast<double>(width()) / vertical_ratio),
+          wallpaper_.height());
+    } else {
+      cropped_size = gfx::Size(wallpaper_.width(),
+          RoundPositive(static_cast<double>(height()) / horizontal_ratio));
+    }
+
+    gfx::Rect wallpaper_cropped_rect = wallpaper_rect.Center(cropped_size);
+    canvas->DrawBitmapInt(wallpaper_,
+       wallpaper_cropped_rect.x(), wallpaper_cropped_rect.y(),
+       wallpaper_cropped_rect.width(), wallpaper_cropped_rect.height(),
+       0, 0, width(), height(),
+       true);
+  }
+  else {

[tfarina, 2012/03/01 17:24:12]

nit: else should be in the of the previous line.

+    // Center the wallpaper in the destination rectangle (Skia will crop
+    // as needed). We might decide later to tile small solid color images.
+    canvas->DrawBitmapInt(wallpaper_, (width() - wallpaper_.width()) / 2,
+        (height() - wallpaper_.height()) / 2);
+  }
 }
 
 bool DesktopBackgroundView::OnMousePressed(const views::MouseEvent& event) {