gpu: Workaround invalid values from GetShaderPrecisionFormat

gpu/command_buffer/service/gles2_cmd_decoder.cc

 // Copyright (c) 2012 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 "gpu/command_buffer/service/gles2_cmd_decoder.h"
 
 #include <stdio.h>
 
 #include <algorithm>
 #include <list>
@@ skipping 67 matching lines @@
 static const char kEXTFragDepthExtension[] = "GL_EXT_frag_depth";
 static const char kEXTDrawBuffersExtension[] = "GL_EXT_draw_buffers";
 
 #if !defined(ANGLE_SH_VERSION) || ANGLE_SH_VERSION < 108
 khronos_uint64_t CityHashForAngle(const char* name, unsigned int len) {
   return static_cast<khronos_uint64_t>(
       CityHash64(name, static_cast<size_t>(len)));
 }
 #endif
 
+static bool PrecisionMeetsSpecForHighpFloat(GLint rangeMin,
+                                            GLint rangeMax,
+                                            GLint precision) {
+  return (rangeMin >= 62) && (rangeMax >= 62) && (precision >= 16);
+}
+
 static void GetShaderPrecisionFormatImpl(GLenum shader_type,
                                          GLenum precision_type,
                                          GLint *range, GLint *precision) {
   switch (precision_type) {
     case GL_LOW_INT:
     case GL_MEDIUM_INT:
     case GL_HIGH_INT:
       // These values are for a 32-bit twos-complement integer format.
       range[0] = 31;
       range[1] = 30;
@@ skipping 15 matching lines @@
   if (gfx::GetGLImplementation() == gfx::kGLImplementationEGLGLES2 &&
       gfx::g_driver_gl.fn.glGetShaderPrecisionFormatFn) {
     // This function is sometimes defined even though it's really just
     // a stub, so we need to set range and precision as if it weren't
     // defined before calling it.
     // On Mac OS with some GPUs, calling this generates a
     // GL_INVALID_OPERATION error. Avoid calling it on non-GLES2
     // platforms.
     glGetShaderPrecisionFormat(shader_type, precision_type,
                                range, precision);
+
+    // TODO(brianderson): Make the following official workarounds.
+
+    // Some drivers have bugs where they report the ranges as a negative number.
+    // Taking the absolute value here shouldn't hurt because negative numbers
+    // aren't expected anyway.
+    range[0] = abs(range[0]);
+    range[1] = abs(range[1]);
+
+    // If the driver reports a precision for highp float that isn't actually
+    // highp, don't pretend like it's supported because shader compilation will
+    // fail anyway.
+    if (precision_type == GL_HIGH_FLOAT &&
+        !PrecisionMeetsSpecForHighpFloat(range[0], range[1], *precision)) {
+      range[0] = 0;
+      range[1] = 0;
+      *precision = 0;
+    }
   }
 }
 
 }  // namespace
 
 class GLES2DecoderImpl;
 
 // Local versions of the SET_GL_ERROR macros
 #define LOCAL_SET_GL_ERROR(error, function_name, msg) \
     ERRORSTATE_SET_GL_ERROR(state_.GetErrorState(), error, function_name, msg)
@@ skipping 2371 matching lines @@
       group_->max_fragment_uniform_vectors();
   resources.MaxDrawBuffers = group_->max_draw_buffers();
   resources.MaxExpressionComplexity = 256;
   resources.MaxCallStackDepth = 256;
 
 #if (ANGLE_SH_VERSION >= 110)
   GLint range[2] = { 0, 0 };
   GLint precision = 0;
   GetShaderPrecisionFormatImpl(GL_FRAGMENT_SHADER, GL_HIGH_FLOAT,
                                range, &precision);
-  resources.FragmentPrecisionHigh = ((range[0] >= 62) &&
-                                     (range[1] >= 62) &&
-                                     (precision >= 16));
+  resources.FragmentPrecisionHigh =
+      PrecisionMeetsSpecForHighpFloat(range[0], range[1], precision);
 #endif
 
   if (force_webgl_glsl_validation_) {
     resources.OES_standard_derivatives = derivatives_explicitly_enabled_;
     resources.EXT_frag_depth = frag_depth_explicitly_enabled_;
     resources.EXT_draw_buffers = draw_buffers_explicitly_enabled_;
   } else {
     resources.OES_standard_derivatives =
         features().oes_standard_derivatives ? 1 : 0;
     resources.ARB_texture_rectangle =
@@ skipping 7793 matching lines @@
   return error::kNoError;
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu