exo: Add Surface::SetBufferScale.

components/exo/surface.cc

Index: components/exo/surface.cc
diff --git a/components/exo/surface.cc b/components/exo/surface.cc
index d822e5b03a59697ebc90f6d5852593e55966a454..e4151cb1a14e3d5693f5e79d0a6ea199244ed7f7 100644
--- a/components/exo/surface.cc
+++ b/components/exo/surface.cc
@@ -19,6 +19,7 @@
 #include "ui/compositor/layer.h"
 #include "ui/gfx/buffer_format_util.h"
 #include "ui/gfx/gpu_memory_buffer.h"
+#include "ui/gfx/transform_util.h"
 
 DECLARE_WINDOW_PROPERTY_TYPE(exo::Surface*);
 
@@ -90,6 +91,7 @@ class EmptyWindowDelegate : public aura::WindowDelegate {
 Surface::Surface()
     : aura::Window(new EmptyWindowDelegate),
       has_pending_contents_(false),
+      pending_buffer_scale_(1.0f),
       needs_commit_surface_hierarchy_(false),
       update_contents_after_successful_compositing_(false),
       compositor_(nullptr),
@@ -149,6 +151,12 @@ void Surface::SetOpaqueRegion(const SkRegion& region) {
   pending_opaque_region_ = region;
 }
 
+void Surface::SetBufferScale(float scale) {
+  TRACE_EVENT1("exo", "Surface::SetBufferScale", "scale", scale);
+
+  pending_buffer_scale_ = scale;
+}
+
 void Surface::AddSubSurface(Surface* sub_surface) {
   TRACE_EVENT1("exo", "Surface::AddSubSurface", "sub_surface",
                sub_surface->AsTracedValue());
@@ -271,10 +279,14 @@ void Surface::CommitSurfaceHierarchy() {
                                  texture_mailbox_release_callback.Pass(),
                                  texture_mailbox.size_in_pixels());
       layer()->SetTextureFlipped(false);
-      layer()->SetBounds(gfx::Rect(layer()->bounds().origin(),
-                                   texture_mailbox.size_in_pixels()));
+      gfx::Size contents_size(gfx::ScaleToFlooredSize(
+          texture_mailbox.size_in_pixels(), 1.0f / pending_buffer_scale_));
+      layer()->SetBounds(gfx::Rect(layer()->bounds().origin(), contents_size));
       layer()->SetFillsBoundsOpaquely(pending_opaque_region_.contains(
-          gfx::RectToSkIRect(gfx::Rect(texture_mailbox.size_in_pixels()))));
+          gfx::RectToSkIRect(gfx::Rect(contents_size))));
+      layer()->SetTransform(gfx::GetScaleTransform(
+          gfx::Rect(texture_mailbox.size_in_pixels()).CenterPoint(),
+          1.0f / pending_buffer_scale_));

[lpique, 2016/01/04 19:36:20]

The call to ScaleToFlooredSize() includes (as the name indicates) flooring to an
integer value.

Shouldn't this set a scale transform of "contents_size /
texture_mailbox.size_in_pixels()" so that the adjusted size is used to set the
scale?

[reveman, 2016/01/05 09:02:48]

Good point. Done.

     } else {
       // Show solid color content if no buffer is attached or we failed
       // to produce a texture mailbox for the currently attached buffer.
@@ -331,7 +343,9 @@ void Surface::CommitSurfaceHierarchy() {
 }
 
 gfx::Size Surface::GetPreferredSize() const {
-  return pending_buffer_ ? pending_buffer_->GetSize() : layer()->size();
+  return pending_buffer_ ? gfx::ScaleToFlooredSize(pending_buffer_->GetSize(),
+                                                   1.0f / pending_buffer_scale_)
+                         : layer()->size();
 }
 
 bool Surface::IsSynchronized() const {