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 102 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);
+
+    // 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 &&
+        (range[0] < 62 || range[1] < 62 || *precision < 16)) {

[Ken Russell (switch to Gerrit), 2013/06/11 20:01:27]

Can the duplicate logic here and in GLES2DecoderImpl::InitializeShaderTranslator
be refactored?

[brianderson, 2013/06/11 23:35:46]

Done.

+      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 2367 matching lines @@
       group_->max_vertex_texture_image_units();
   resources.MaxCombinedTextureImageUnits = group_->max_texture_units();
   resources.MaxTextureImageUnits = group_->max_texture_image_units();
   resources.MaxFragmentUniformVectors =
       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 };

[greggman, 2013/06/11 21:58:50]

What kbr said, should this code have the same workaround? Should call some
function so the workaround is in one place?

[brianderson, 2013/06/11 23:35:46]

The workaround is in GetShaderPrecisionFormatImpl so it is also used here,
however in the second patch I have put the magic numbers 62,62,16 into a common
function.

   GLint precision = 0;
   GetShaderPrecisionFormatImpl(GL_FRAGMENT_SHADER, GL_HIGH_FLOAT,
                                range, &precision);
   resources.FragmentPrecisionHigh = ((range[0] >= 62) &&
                                      (range[1] >= 62) &&
                                      (precision >= 16));
 #endif
 
   if (force_webgl_glsl_validation_) {
     resources.OES_standard_derivatives = derivatives_explicitly_enabled_;
@@ skipping 7799 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