tree 3de47f38e29f692ba86d4a549b52730143a5adb0
parent c39e7c7cc8844e2b75bdc7e58ea5e1c68b318ad9
author Nicolas Capens <capn@google.com> 1564522076 -0400
committer Nicolas Capens <nicolascapens@google.com> 1564528809 +0000

Use a finite maxSamplerLodBias limit

We previously set this device limit to infinity to avoid having to
clamp the sum of the sampler and shader provided bias values to the
[-maxSamplerLodBias, maxSamplerLodBias] range. Unfortunately infinity
is not supported/allowed by JSON and the android.graphics.cts.VulkanFeaturesTest
tests which parse the output of the vkjson tool produce a failure.

This change works around it by setting maxSamplerLodBias to a finite
value (15, which is very common according to https://vulkan.gpuinfo.org/),
and performing the clamping required by Vulkan 1.1.117 section 15.6.7.
Fortunately this cost only has to be incurred when an optional Bias
operand is used in the SPIR-V image sampling instruction. When an Lod
operand is used, which is mutually exclusive with Bias because the
former is for explicit-lod instructions and the latter for implicit-lod,
no clamping is required because the explicit LOD is not part of this
clamping equation and the sampler LOD bias must already be clamped as
specified by the spec: "The absolute value of mipLodBias must be less
than or equal to VkPhysicalDeviceLimits::maxSamplerLodBias".

Bug: b/138670766
Change-Id: Iebd6a1fef1c993ec86ac8cc38f8d9a992ba9bc47
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/34510
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>