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 bd535a8a23811006d8ed01759a4749986972e26b..45a4c60500aaeaaf93271820354a50c744b647b1 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -33,10 +33,50 @@ 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(
+          static_cast<int>(static_cast<double>(width()) / vertical_ratio),

[Daniel Erat, 2012/02/29 21:41:40]

nit: round this?

[Emmanuel Saint-loubert-Bié, 2012/02/29 22:04:16]

Do you mean using floor() or similar function and applying to the "double"
resulting from the division?

[Daniel Erat, 2012/02/29 22:10:40]

i meant doing static_cast<int>(round(...)) on the result of the division.  the
static_cast<int> that you're currently doing is pretty much the same as calling
floor(), but i think it'd be more accurate to round.

+          wallpaper_.height());
+    } else {
+      cropped_size = gfx::Size(wallpaper_.width(),
+          static_cast<int>(static_cast<double>(height()) / horizontal_ratio));

[Daniel Erat, 2012/02/29 21:41:40]

nit: round?

+    }
+
+    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 {
+    // Center the wallpaper and crop to the destination rectangle.

[Daniel Erat, 2012/02/29 21:41:40]

have you tested whether it's okay for the destination coordinates to fall
outside of the destination bounds (i.e. will skia do the clipping for you)?  if
so, you could probably just do:

  canvas->DrawBitmapInt(
      wallpaper_,
      (width() - wallpaper_.width()) / 2,
      (height() - wallpaper_.height()) / 2);

[Emmanuel Saint-loubert-Bié, 2012/02/29 22:04:16]

Ha yes that works too, much clearer. I applied your suggestion.

+    gfx::Rect wallpaper_centered_rect = wallpaper_rect.Center(gfx::Size(
+        std::min(wallpaper_.width(), width()),
+        std::min(wallpaper_.height(), height())));
+    canvas->DrawBitmapInt(wallpaper_,
+       wallpaper_centered_rect.x(), wallpaper_centered_rect.y(),
+       wallpaper_centered_rect.width(), wallpaper_centered_rect.height(),
+       std::max(0, (width() - wallpaper_centered_rect.width()) / 2),
+       std::max(0, (height() - wallpaper_centered_rect.height()) / 2),
+       wallpaper_centered_rect.width(), wallpaper_centered_rect.height(),
+       true);
+  }
 }
 
 bool DesktopBackgroundView::OnMousePressed(const views::MouseEvent& event) {