Infer sampler precision from pixel config

src/gpu/vk/GrVkCaps.cpp

Index: src/gpu/vk/GrVkCaps.cpp
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index 8f46408706e8f22eeb1e9f048c432596bc514355..1ddeeb8a94b7f82d84f25b3370b881e8acf433ee 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -153,6 +153,23 @@ void GrVkCaps::initGLSLCaps(const VkPhysicalDeviceProperties& properties,
 #endif
     glslCaps->fIntegerSupport = true;
 
+    // Assume the minimum precisions mandated by the GLSL spec for now.
+    glslCaps->fShaderPrecisionVaries = true;
+    for (int s = 0; s < kGrShaderTypeCount; ++s) {

[egdaniel, 2016/04/05 21:09:48]

in vulkan/SPIR-V,

highp in glsl maps to 32 bit float t IEEE 754 floating-point.
lowp/mediump maps to RelexedPrecision, see SPIR-V spec
(https://www.khronos.org/registry/spir-v/specs/1.0/SPIRV.pdf) for minimum
requirements for this precsion.

[Chris Dalton, 2016/04/05 21:54:49]

Done.

+        auto& lowp = glslCaps->fFloatPrecisions[s][kLow_GrSLPrecision];
+        lowp.fLogRangeLow = lowp.fLogRangeHigh = 1;
+        lowp.fBits = 8;
+
+        auto& mediump = glslCaps->fFloatPrecisions[s][kLow_GrSLPrecision];
+        mediump.fLogRangeLow = lowp.fLogRangeHigh = 14;
+        mediump.fBits = 10;
+
+        auto& highp = glslCaps->fFloatPrecisions[s][kLow_GrSLPrecision];
+        highp.fLogRangeLow = highp.fLogRangeHigh = 62;
+        highp.fBits = 16;
+    }
+    glslCaps->initEffectiveFloatPrecisionTable();
+
     glslCaps->fMaxVertexSamplers =
     glslCaps->fMaxGeometrySamplers =
     glslCaps->fMaxFragmentSamplers = SkTMin(properties.limits.maxPerStageDescriptorSampledImages,