Device-Generated Commands

This chapter discusses the generation of command buffer content on the device, for which these principle steps are to be taken:

• Define via VkIndirectCommandsLayoutNV the sequence of commands which should be generated.
• Optionally make use of device-bindable Shader Groups for graphics pipelines.
• Retrieve device addresses by vkGetBufferDeviceAddressEXT for setting buffers on the device.
• Retrieve device addresses of compute pipelines by vkGetPipelineIndirectDeviceAddressNV to be able to bind it in device generated rendering.
• Fill one or more VkBuffer with the appropriate content that gets interpreted by VkIndirectCommandsLayoutNV.
• Create a preprocess VkBuffer using the allocation information from vkGetGeneratedCommandsMemoryRequirementsNV.
• Optionally preprocess the input data using vkCmdPreprocessGeneratedCommandsNV in a separate action.
• Generate and execute the actual commands via vkCmdExecuteGeneratedCommandsNV passing all required data.

vkCmdPreprocessGeneratedCommandsNV executes in a separate logical pipeline from either graphics or compute. When preprocessing commands in a separate step they must be explicitly synchronized against the command execution. When not preprocessing, the preprocessing is automatically synchronized against the command execution.

Indirect Commands Layout

Creation and Deletion

Token Input Streams

The input streams can contain raw uint32_t values, existing indirect commands such as:

• VkDrawIndirectCommand
• VkDrawIndexedIndirectCommand
• VkDrawMeshTasksIndirectCommandNV
• VkDrawMeshTasksIndirectCommandEXT
• VkDispatchIndirectCommand

or additional commands as listed below. How the data is used is described in the next section.

Tokenized Command Processing

The processing is in principle illustrated below:

The processing of each sequence is considered stateless, therefore all state changes must occur before any action command tokens within the sequence. A single sequence is strictly targeting the VkPipelineBindPoint it was created with.

The primary input data for each token is provided through VkBuffer content at preprocessing using vkCmdPreprocessGeneratedCommandsNV or execution time using vkCmdExecuteGeneratedCommandsNV, however some functional arguments, for example binding sets, are specified at layout creation time. The input size is different for each token.

The following code provides detailed information on how an individual sequence is processed. For valid usage, all restrictions from the regular commands apply.

Indirect Commands Generation and Execution

To bind a compute pipeline in Device-Generated Commands, an application must query the pipeline’s device address.

Referencing the functions defined in Indirect Commands Layout, vkCmdExecuteGeneratedCommandsNV behaves as:

The bound descriptor sets and push constants that will be used with indirect command generation for the compute pipelines must already be specified at the time of preprocessing commands with vkCmdPreprocessGeneratedCommandsNV. They must not change until the execution of indirect commands is submitted with vkCmdExecuteGeneratedCommandsNV.

If push constants for the compute pipeline are also specified in the VkGeneratedCommandsInfoNV::indirectCommandsLayout with VK_INDIRECT_COMMANDS_TOKEN_TYPE_PUSH_CONSTANT_NV token, then those values override the push constants that were previously pushed for the compute pipeline.