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

cc/base/switches.cc

Index: cc/base/switches.cc
diff --git a/cc/base/switches.cc b/cc/base/switches.cc
index 1fb7ac98e37d6b3b87e1431a530bd25cd16a291e..277b6fccf42e9c3f538e89b858e130e507730471 100644
--- a/cc/base/switches.cc
+++ b/cc/base/switches.cc
@@ -4,6 +4,8 @@
 
 #include "cc/base/switches.h"
 
+#include <string>
+
 #include "base/command_line.h"
 
 namespace cc {
@@ -36,14 +38,11 @@ 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";
@@ -165,15 +164,22 @@ bool IsLCDTextEnabled() {
 #endif
 }
 
-bool IsGpuRasterizationEnabled() {
+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";
+}
 
-  if (command_line.HasSwitch(switches::kDisableGPURasterization))
+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.

-  else if (command_line.HasSwitch(switches::kEnableGPURasterization))
-    return true;
-
-  return false;
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+  std::string rasterization_site =
+      command_line.GetSwitchValueASCII(switches::kRasterizationSite);
+  return rasterization_site == "gpu";
 }
 
 bool IsImplSidePaintingEnabled() {