Add 16-bit fallback to MDI.

Author: Themaister

assets/shaders/decode/meshlet_decode.comp

@@ -10,6 +10,7 @@ layout(constant_id = 0) const uint NUM_U32_STREAMS = MESHLET_PAYLOAD_MAX_STREAMS
 layout(constant_id = 1) const bool UNROLLED_MESH = false;
 layout(constant_id = 2) const uint TARGET_MESH_STYLE = 0;
 layout(constant_id = 3) const bool RUNTIME_MESH = false;
+layout(constant_id = 4) const bool INDEX16 = false;
 
 #include "../inc/global_bindings.h"
 #undef BINDING_GLOBAL_SCENE_MESHLET_STREAM_HEADER_BUFFER
@@ -29,6 +30,11 @@ layout(set = 0, binding = 2, scalar) writeonly buffer OutputIndices
     uvec3 data[];
 } output_indices32;
 
+layout(set = 0, binding = 2, scalar) writeonly buffer OutputIndices16
+{
+    u16vec3 data[];
+} output_indices16;
+
 layout(set = 0, binding = 2, scalar) writeonly buffer OutputIndices8
 {
     u8vec3 data[];
@@ -117,6 +123,8 @@ void main()
 
         if (UNROLLED_MESH)
             output_indices32.data[offsets.primitive_output_offset + lane_index] = indices;
+        else if (INDEX16)
+            output_indices16.data[offsets.primitive_output_offset + lane_index] = u16vec3(indices);
         else
             output_indices8.data[offsets.primitive_output_offset + lane_index] = u8vec3(indices);
     }

renderer/renderer.cpp

@@ -674,10 +674,15 @@ void Renderer::render_mesh_assets(Vulkan::CommandBuffer &cmd, const RenderContex
 		auto *pos = manager.get_position_buffer();
 		auto *attr = manager.get_attribute_buffer();
 
-		cmd.set_index_buffer(*ibo, 0,
-		                     encoding == ResourceManager::MeshEncoding::Classic
-			                     ? VK_INDEX_TYPE_UINT32
-			                     : VK_INDEX_TYPE_UINT8);
+		VkIndexType index_type;
+		if (encoding == ResourceManager::MeshEncoding::Classic)
+			index_type = VK_INDEX_TYPE_UINT32;
+		else if (device->get_device_features().vk14_features.indexTypeUint8)
+			index_type = VK_INDEX_TYPE_UINT8;
+		else
+			index_type = VK_INDEX_TYPE_UINT16;
+
+		cmd.set_index_buffer(*ibo, 0, index_type);
 
 		cmd.set_vertex_binding(0, *pos, 0, 12);
 		cmd.set_vertex_binding(1, *attr, 0, 16);

vulkan/managers/resource_manager.cpp

@@ -143,7 +143,15 @@ void ResourceManager::init_mesh_assets()
 
 	if (mesh_encoding != MeshEncoding::MeshletEncoded)
 	{
-		unsigned index_size = mesh_encoding == MeshEncoding::Classic ? sizeof(uint32_t) : sizeof(uint8_t);
+		unsigned index_size;
+
+		if (mesh_encoding == MeshEncoding::Classic)
+			index_size = sizeof(uint32_t);
+		else if (device->get_device_features().vk14_features.indexTypeUint8)
+			index_size = sizeof(uint8_t);
+		else
+			index_size = sizeof(uint16_t);
+
 		index_buffer_allocator.set_element_size(0, 3 * index_size); // 8-bit or 32-bit indices.
 		attribute_buffer_allocator.set_soa_count(3);
 		attribute_buffer_allocator.set_element_size(0, sizeof(float) * 3);
@@ -547,6 +555,8 @@ void ResourceManager::instantiate_asset_mesh(Granite::AssetManager &manager_,
 			info.target_style = view.format_header->style;
 			if (mesh_encoding == MeshEncoding::Classic)
 				info.flags |= Meshlet::DECODE_MODE_UNROLLED_MESH;
+			else if (!device->get_device_features().vk14_features.indexTypeUint8)
+				info.flags |= Meshlet::DECODE_MODE_INDEX_16;
 			info.ibo = index_buffer_allocator.get_buffer(0, 0);
 
 			for (unsigned i = 0; i < 3; i++)

vulkan/mesh/meshlet.cpp

@@ -196,11 +196,12 @@ bool decode_mesh(CommandBuffer &cmd, const DecodeInfo &info, const MeshView &vie
 	cmd.set_storage_buffer(0, 1, *info.payload);
 	cmd.set_storage_buffer(0, 2, *info.ibo);
 
-	cmd.set_specialization_constant_mask(0xf);
+	cmd.set_specialization_constant_mask(0x1f);
 	cmd.set_specialization_constant(0, view.format_header->stream_count);
 	cmd.set_specialization_constant(1, (info.flags & DECODE_MODE_UNROLLED_MESH) != 0);
 	cmd.set_specialization_constant(2, uint32_t(info.target_style));
 	cmd.set_specialization_constant(3, uint32_t(meshlet_runtime));
+	cmd.set_specialization_constant(4, (info.flags & DECODE_MODE_INDEX_16) != 0);
 
 	for (unsigned i = 0; i < 3; i++)
 		cmd.set_storage_buffer(0, 3 + i, info.streams[i] ? *info.streams[i] : *info.streams[0]);

vulkan/mesh/meshlet.hpp

@@ -130,6 +130,7 @@ MeshView create_mesh_view(const Granite::FileMapping &mapping);
 enum DecodeModeFlagBits : uint32_t
 {
 	DECODE_MODE_UNROLLED_MESH = 1 << 0,
+	DECODE_MODE_INDEX_16 = 1 << 1,
 };
 using DecodeModeFlags = uint32_t;