cc: Cache highp_threshold in TexCoordPrecisionRequired

cc/output/shader.cc

 // Copyright 2011 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/output/shader.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
@@ skipping 63 matching lines @@
   // we are unlikely to be vertex shader bound when drawing large quads.
   // Also, some vertex shaders mutate the texture coordinate in such a
   // way that the effective precision might be lower than expected.
   return "#define TexCoordPrecision highp\n" +
       std::string(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;
 }
 
 }  // namespace
 
 TexCoordPrecision TexCoordPrecisionRequired(WebGraphicsContext3D* context,
                                             int highp_threshold_min,
                                             gfx::Point max_coordinate) {
   return TexCoordPrecisionRequired(context, highp_threshold_min,
@@ skipping 1324 matching lines @@
       vec2 texCoord =
           clamp(v_texCoord, 0.0, 1.0) * texTransform.zw + texTransform.xy;
       vec2 coord = mod(floor(texCoord * frequency * 2.0), 2.0);
       float picker = abs(coord.x - coord.y);
       gl_FragColor = mix(color1, color2, picker) * alpha;
     }
   );  // NOLINT(whitespace/parens)
 }
 
 }  // namespace cc