command_buffer: Implement path rendering functions for CHROMIUM_path_rendering

gpu/command_buffer/service/feature_info.cc

Index: gpu/command_buffer/service/feature_info.cc
diff --git a/gpu/command_buffer/service/feature_info.cc b/gpu/command_buffer/service/feature_info.cc
index c747383ee818f090e2d061493253a1a784ade3d3..e6df3d4a608e7ecdd5990116901d60683e415eb3 100644
--- a/gpu/command_buffer/service/feature_info.cc
+++ b/gpu/command_buffer/service/feature_info.cc
@@ -209,6 +209,9 @@ void FeatureInfo::InitializeBasicState(const base::CommandLine& command_line) {
   enable_unsafe_es3_apis_switch_ =
       command_line.HasSwitch(switches::kEnableUnsafeES3APIs);
 
+  enable_gl_path_rendering_switch_ =
+      command_line.HasSwitch(switches::kEnableGLPathRendering);
+
   unsafe_es3_apis_enabled_ = false;
 }
 
@@ -1004,13 +1007,22 @@ void FeatureInfo::InitializeFeatures() {
     }
   }
 
-  if (extensions.Contains("GL_NV_path_rendering")) {
-    if (extensions.Contains("GL_EXT_direct_state_access") ||
-        gl_version_info_->is_es3) {
+  if (enable_gl_path_rendering_switch_ &&
+      extensions.Contains("GL_NV_path_rendering")) {
+    bool hasNeededOptionalFunctions =
+        gfx::GetGLProcAddress("glStencilThenCoverFillPathNV") &&
+        gfx::GetGLProcAddress("glStencilThenCoverStrokePathNV");

[piman, 2015/06/27 01:20:07]

Why is this needed?

[Kimmo Kinnunen, 2015/06/29 05:46:04]

These required functions are part of the API version 1.2.  For
older drivers, these do not exist, even though the extension
string is the same. In theory these particular functions could be simulated if
missing. In patch #3 of the patchset, texturing, there will be use of API
version 1.3, which can not be simulated. This is why I did not implement the
simulation.

[piman, 2015/06/29 23:31:17]

I don't much like this idea of extension "API version"... It sounds like older
drivers are exposing an extension string without implementing the extension as
documented on the registry
(https://www.khronos.org/registry/gles/extensions/NV/path_rendering.txt), which
is really a driver bug.

I would actually prefer if we blacklisted the extension on older driver versions
using the workarounds mechanism (gpu/config/gpu_driver_bug_list_json.cc). This
is fragile, we mock the GetProcAddress function in some environments.

+
+    if (hasNeededOptionalFunctions &&
+        (extensions.Contains("GL_EXT_direct_state_access") ||
+         gl_version_info_->is_es3)) {
       AddExtensionString("GL_CHROMIUM_path_rendering");
       feature_flags_.chromium_path_rendering = true;
       validators_.g_l_state.AddValue(GL_PATH_MODELVIEW_MATRIX_CHROMIUM);
       validators_.g_l_state.AddValue(GL_PATH_PROJECTION_MATRIX_CHROMIUM);
+      validators_.g_l_state.AddValue(GL_PATH_STENCIL_FUNC_CHROMIUM);
+      validators_.g_l_state.AddValue(GL_PATH_STENCIL_REF_CHROMIUM);
+      validators_.g_l_state.AddValue(GL_PATH_STENCIL_VALUE_MASK_CHROMIUM);
     }
   }