Work around problems with explicit LoD with arrayed depth images on Apple Silicon.

Use an explicit gradient to make it sample the correct level.

Update SPIRV-Cross to pull in the change needed for this.

Docs/Whats_New.md

@@ -20,6 +20,8 @@ Released TBA
 
 - Fix issue where extension `VK_KHR_fragment_shader_barycentric` 
   was sometimes incorrectly disabled due to a Metal driver bug.
+- Work around problems with using explicit LoD with arrayed depth images
+  on Apple Silicon.
 
 
 

ExternalRevisions/SPIRV-Cross_repo_revision

@@ -1 +1 @@
-eb9b2732982b8eea3395216be825a74dd84fe4be
+4e2fdb25671c742a9fbe93a6034eb1542244c7e1

MoltenVK/MoltenVK/API/vk_mvk_moltenvk.h

@@ -979,6 +979,7 @@ typedef struct {
 	VkBool32 programmableSamplePositions;			/**< If true, programmable MSAA sample positions are supported. */
 	VkBool32 shaderBarycentricCoordinates;			/**< If true, fragment shader barycentric coordinates are supported. */
 	MTLArgumentBuffersTier argumentBuffersTier;		/**< The argument buffer tier available on this device, as a Metal enumeration. */
+	VkBool32 needsSampleDrefLodArrayWorkaround;		/**< If true, sampling from arrayed depth images with explicit LoD is broken and needs a workaround. */
 } MVKPhysicalDeviceMetalFeatures;
 
 /** MoltenVK performance of a particular type of activity. */

MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm

@@ -1493,6 +1493,9 @@ void MVKPhysicalDevice::initMetalFeatures() {
 			_metalFeatures.clearColorFloatRounding = MVK_FLOAT_ROUNDING_DOWN;
 			break;
 		case kAppleVendorId:
+			// TODO: Other GPUs?
+			_metalFeatures.needsSampleDrefLodArrayWorkaround = true;
+			// fallthrough
 		case kIntelVendorId:
 		case kNVVendorId:
 		default:

MoltenVK/MoltenVK/GPUObjects/MVKPipeline.mm

@@ -1152,6 +1152,9 @@ bool MVKGraphicsPipeline::addFragmentShaderToPipeline(MTLRenderPipelineDescripto
 		shaderConfig.options.mslOptions.capture_output_to_buffer = false;
 		shaderConfig.options.mslOptions.fixed_subgroup_size = mvkIsAnyFlagEnabled(_pFragmentSS->flags, VK_PIPELINE_SHADER_STAGE_CREATE_ALLOW_VARYING_SUBGROUP_SIZE_BIT_EXT) ? 0 : _device->_pMetalFeatures->maxSubgroupSize;
 		shaderConfig.options.mslOptions.check_discarded_frag_stores = true;
+		if (_device->_pMetalFeatures->needsSampleDrefLodArrayWorkaround) {
+			shaderConfig.options.mslOptions.sample_dref_lod_array_as_grad = true;
+		}
 		if (_isRasterizing && pCreateInfo->pMultisampleState) {		// Must ignore allowed bad pMultisampleState pointer if rasterization disabled
 			if (pCreateInfo->pMultisampleState->pSampleMask && pCreateInfo->pMultisampleState->pSampleMask[0] != 0xffffffff) {
 				shaderConfig.options.mslOptions.additional_fixed_sample_mask = pCreateInfo->pMultisampleState->pSampleMask[0];
@@ -2253,7 +2256,8 @@ namespace SPIRV_CROSS_NAMESPACE {
 				opt.vertex_index_type,
 				opt.force_sample_rate_shading,
 				opt.manual_helper_invocation_updates,
-				opt.check_discarded_frag_stores);
+				opt.check_discarded_frag_stores,
+				opt.sample_dref_lod_array_as_grad);
 	}
 
 	template<class Archive>