cc: Trigger GPU rasterization based on a per-layer hint

cc/base/switches.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 "cc/base/switches.h"
 
+#include <string>
+
 #include "base/command_line.h"
 
 namespace cc {
 namespace switches {
 
 // On platforms where checkerboards are used, prefer background colors instead
 // of checkerboards.
 const char kBackgroundColorInsteadOfCheckerboard[] =
     "background-color-instead-of-checkerboard";
 
@@ skipping 12 matching lines @@
 
 // Enables LCD text.
 const char kEnableLCDText[] = "enable-lcd-text";
 
 // Paint content on the compositor thread instead of the main thread.
 const char kEnableImplSidePainting[] = "enable-impl-side-painting";
 
 const char kEnableTopControlsPositionCalculation[] =
     "enable-top-controls-position-calculation";
 
-// Allow heuristics to determine when a layer tile should be drawn with
-// the Skia GPU backend.  Only valid with GPU accelerated compositing +
-// impl-side painting.
-const char kEnableGPURasterization[] = "enable-gpu-rasterization";
-
-// Disable GPU rasterization, i.e. rasterize on the CPU only.
-// Overrides the kEnableGPURasterization flag.
-const char kDisableGPURasterization[] = "disable-gpu-rasterization";
+// Select the location used for drawing layer tiles. Allowed values are
+// 'cpu' (rasterize on the CPU only), 'gpu' (always use the Skia GPU backend
+// for rasterization), and 'hybrid' (use hints and heuristics to determine
+// when to rasterize using the Skia GPU backend).
+const char kRasterizationSite[] = "rasterization-site";
 
 // The height of the movable top controls.
 const char kTopControlsHeight[] = "top-controls-height";
 
 // Percentage of the top controls need to be hidden before they will auto hide.
 const char kTopControlsHideThreshold[] = "top-controls-hide-threshold";
 
 // Percentage of the top controls need to be shown before they will auto show.
 const char kTopControlsShowThreshold[] = "top-controls-show-threshold";
 
@@ skipping 101 matching lines @@
   else if (command_line->HasSwitch(switches::kEnableLCDText))
     return true;
 
 #if defined(OS_ANDROID)
   return false;
 #else
   return true;
 #endif
 }
 
+bool IsHybridRasterizationEnabled() {
+  if (!IsImplSidePaintingEnabled())
+    return false;
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  std::string rasterization_site =
+      command_line.GetSwitchValueASCII(switches::kRasterizationSite);
+  return rasterization_site == "hybrid";
+}
+
 bool IsGpuRasterizationEnabled() {
+  if (!IsImplSidePaintingEnabled())
+    return false;

[piman, 2014/03/06 22:13:53]

I think all these flags and helper functions should be in content/

Having them in cc/ suggests they apply to both the browser compositor and the
renderer compositor, whereas they only apply to the latter.

They're also not accurate since gpu rasterization is only enabled if
--enable-bleeding-edge-rendering-fast-paths is set as well.

The temptation is high to use them inside of cc/ and cause issues because of
mismatches.

My suggestion is to move the flags to content_flags.cc, and the helper functions
to somewhere on content/renderer (e.g. maybe bools on RenderThreadImpl), and
have them accurately reflect the full policy..

[ernstm, 2014/03/06 22:47:26]

GPU rasterization can be enabled without setting
--enable-bleeding-edge-rendering-fast-paths. As I understand it,
--enable-bleeding-edge-rendering-fast-paths is just a shortcut to enable a
collection of features with a single flag.

   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-
-  if (command_line.HasSwitch(switches::kDisableGPURasterization))
-    return false;
-  else if (command_line.HasSwitch(switches::kEnableGPURasterization))
-    return true;
-
-  return false;
+  std::string rasterization_site =
+      command_line.GetSwitchValueASCII(switches::kRasterizationSite);
+  return rasterization_site == "gpu";
 }
 
 bool IsImplSidePaintingEnabled() {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
 
   if (command_line.HasSwitch(switches::kDisableImplSidePainting))
     return false;
   else if (command_line.HasSwitch(switches::kEnableImplSidePainting))
     return true;
 
@@ skipping 10 matching lines @@
   if (command_line.HasSwitch(switches::kDisableMapImage))
     return false;
   else if (command_line.HasSwitch(switches::kEnableMapImage))
     return true;
 
   return false;
 }
 
 }  // namespace switches
 }  // namespace cc