cc: Cache highp_threshold in TexCoordPrecisionRequired

cc/output/shader.cc

Index: cc/output/shader.cc
diff --git a/cc/output/shader.cc b/cc/output/shader.cc
index 2226192d9af9a6840e64be959452c9df71154193..be0c3c02a20eb42ab24de70f11da8abce6f8dd6b 100644
--- a/cc/output/shader.cc
+++ b/cc/output/shader.cc
@@ -81,17 +81,27 @@ static std::string SetVertexTexCoordPrecision(const char* shader_string) {
 TexCoordPrecision TexCoordPrecisionRequired(WebGraphicsContext3D* context,
                                             int highp_threshold_min,
                                             int x, int y) {
-  // Initialize range and precision with minimum spec values for when
-  // GetShaderPrecisionFormat is a test stub.
-  // TODO(brianderson): Implement better stubs of GetShaderPrecisionFormat
-  // everywhere.
-  GLint range[2] = { 14, 14 };
-  GLint precision = 10;
-  GLC(context, context->getShaderPrecisionFormat(GL_FRAGMENT_SHADER,
-                                                 GL_MEDIUM_FLOAT,
-                                                 range, &precision));
-  int highp_threshold = std::max(1 << precision, highp_threshold_min);
-  if (x > highp_threshold || y > highp_threshold)
+  static int s_highp_threshold = 0;
+  static WebGraphicsContext3D* s_cached_context = NULL;
+
+  if (!s_cached_context) {
+    // Initialize range and precision with minimum spec values for when
+    // GetShaderPrecisionFormat is a test stub.
+    // TODO(brianderson): Implement better stubs of GetShaderPrecisionFormat
+    // everywhere.
+    static GLint range[2] = { 14, 14 };
+    static GLint precision = 10;
+    GLC(context, context->getShaderPrecisionFormat(GL_FRAGMENT_SHADER,
+                                                   GL_MEDIUM_FLOAT,
+                                                   range, &precision));
+    s_highp_threshold = std::max(1 << precision, highp_threshold_min);
+    s_cached_context = context;
+  }
+
+  // If we are using multiple contexts, we need smarter caching logic.
+  DCHECK_EQ(s_cached_context, context);

[vangelis, 2013/05/03 19:13:27]

It's not uncommon for one renderer to have multiple contexts instantiated so
this assert will trigger. The real check would be whether they would return
different results but I suspect that'd be rare.

I'd also be a bit concerned about caching a pointer context into a static (just
for doing this assert). Maybe skip it overall? 

+
+  if (x > s_highp_threshold || y > s_highp_threshold)
     return TexCoordPrecisionHigh;
   return TexCoordPrecisionMedium;
 }