gpu: Workaround invalid values from GetShaderPrecisionFormat

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 2363e5346ee01712513a0217ae6e0ece0652a12c..bf217f67e0bb2bfa879b2c1a3bf604450852e564 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -120,6 +120,22 @@ static void GetShaderPrecisionFormatImpl(GLenum shader_type,
     // 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;
+    }
   }
 }