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 61 matching lines @@
 static std::string SetVertexTexCoordPrecision(const char* shader_string) {
   // We unconditionally use highp in the vertex shader since
   // 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_cache,
                                             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)
+  if (*highp_threshold_cache == 0) {

[vangelis, 2013/05/03 22:08:33]

I think you'll need to add: 
|| *highp_threashold_cache > highp_threshold_min

to guard against having this function called with a lower highp_threshold_min
after the result is cached.

+    // 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;

[vangelis, 2013/05/03 22:08:33]

Do these need to be static? 

+    GLC(context, context->getShaderPrecisionFormat(GL_FRAGMENT_SHADER,
+                                                   GL_MEDIUM_FLOAT,
+                                                   range, &precision));
+    *highp_threshold_cache = std::max(1 << precision, highp_threshold_min);
+  }
+
+  if (x > *highp_threshold_cache || y > *highp_threshold_cache)
     return TexCoordPrecisionHigh;
   return TexCoordPrecisionMedium;
 }
 
 }  // namespace
 
 TexCoordPrecision TexCoordPrecisionRequired(WebGraphicsContext3D* context,
+                                            int *highp_threshold_cache,
                                             int highp_threshold_min,
                                             gfx::Point max_coordinate) {
-  return TexCoordPrecisionRequired(context, highp_threshold_min,
+  return TexCoordPrecisionRequired(context,
+                                   highp_threshold_cache, highp_threshold_min,
                                    max_coordinate.x(), max_coordinate.y());
 }
 
 TexCoordPrecision TexCoordPrecisionRequired(WebGraphicsContext3D* context,
+                                            int *highp_threshold_cache,
                                             int highp_threshold_min,
                                             gfx::Size max_size) {
-  return TexCoordPrecisionRequired(context, highp_threshold_min,
+  return TexCoordPrecisionRequired(context,
+                                   highp_threshold_cache, highp_threshold_min,
                                    max_size.width(), max_size.height());
 }
 
 VertexShaderPosTex::VertexShaderPosTex()
       : matrix_location_(-1) {}
 
 void VertexShaderPosTex::Init(WebGraphicsContext3D* context,
                               unsigned program,
                               bool using_bind_uniform,
                               int* base_uniform_index) {
@@ skipping 1307 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