The hardware ignores the LOD for unnormalized coordinates and samples the
base level. A sampler used only by explicit-LOD, implicit-LOD, bias and
gradient samples gets a pipeline specialization constant set from its
unnormalized bit when the binding plan is prepared. When the constant is
set, each of its samples is emitted as OpImageSampleExplicitLod with LOD 0,
which is what Vulkan requires of unnormalized samplers. Otherwise the
sample keeps its own form. Such shaders are no longer refused.
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