vkCmdDrawIndirectByteCountEXT(3)

Name

vkCmdDrawIndirectByteCountEXT - Draw primitives with indirect parameters where the vertex count is derived from the counter byte value in the counter buffer

C Specification

To record a non-indexed draw call, where the vertex count is based on a byte count read from a buffer and the passed in vertex stride parameter, call:

// Provided by VK_EXT_transform_feedback
void vkCmdDrawIndirectByteCountEXT(
    VkCommandBuffer                             commandBuffer,
    uint32_t                                    instanceCount,
    uint32_t                                    firstInstance,
    VkBuffer                                    counterBuffer,
    VkDeviceSize                                counterBufferOffset,
    uint32_t                                    counterOffset,
    uint32_t                                    vertexStride);

Parameters

  • commandBuffer is the command buffer into which the command is recorded.

  • instanceCount is the number of instances to draw.

  • firstInstance is the instance ID of the first instance to draw.

  • counterBuffer is the buffer handle from where the byte count is read.

  • counterBufferOffset is the offset into the buffer used to read the byte count, which is used to calculate the vertex count for this draw call.

  • counterOffset is subtracted from the byte count read from the counterBuffer at the counterBufferOffset

  • vertexStride is the stride in bytes between each element of the vertex data that is used to calculate the vertex count from the counter value. This value is typically the same value that was used in the graphics pipeline state when the transform feedback was captured as the XfbStride.

Description

When the command is executed, primitives are assembled in the same way as done with vkCmdDraw except the vertexCount is calculated based on the byte count read from counterBuffer at offset counterBufferOffset. The assembled primitives execute the bound graphics pipeline.

The effective vertexCount is calculated as follows:

const uint32_t * counterBufferPtr = (const uint8_t *)counterBuffer.address + counterBufferOffset;
vertexCount = floor(max(0, (*counterBufferPtr - counterOffset)) / vertexStride);

The effective firstVertex is zero.

Valid Usage

  • VUID-vkCmdDrawIndirectByteCountEXT-transformFeedback-02287
    VkPhysicalDeviceTransformFeedbackFeaturesEXT::transformFeedback must be enabled

  • VUID-vkCmdDrawIndirectByteCountEXT-transformFeedbackDraw-02288
    The implementation must support VkPhysicalDeviceTransformFeedbackPropertiesEXT::transformFeedbackDraw

  • VUID-vkCmdDrawIndirectByteCountEXT-vertexStride-02289
    vertexStride must be greater than 0 and less than or equal to VkPhysicalDeviceTransformFeedbackPropertiesEXT::maxTransformFeedbackBufferDataStride

  • VUID-vkCmdDrawIndirectByteCountEXT-counterBuffer-04567
    If counterBuffer is non-sparse then it must be bound completely and contiguously to a single VkDeviceMemory object

  • VUID-vkCmdDrawIndirectByteCountEXT-counterBuffer-02290
    counterBuffer must have been created with the VK_BUFFER_USAGE_INDIRECT_BUFFER_BIT usage flag set

  • VUID-vkCmdDrawIndirectByteCountEXT-counterBufferOffset-04568
    counterBufferOffset must be a multiple of 4

  • VUID-vkCmdDrawIndirectByteCountEXT-counterOffset-09474
    counterOffset must be a multiple of 4

  • VUID-vkCmdDrawIndirectByteCountEXT-vertexStride-09475
    vertexStride must be a multiple of 4

  • VUID-vkCmdDrawIndirectByteCountEXT-commandBuffer-02646
    commandBuffer must not be a protected command buffer

Valid Usage (Implicit)

  • VUID-vkCmdDrawIndirectByteCountEXT-commandBuffer-parameter
    commandBuffer must be a valid VkCommandBuffer handle

  • VUID-vkCmdDrawIndirectByteCountEXT-counterBuffer-parameter
    counterBuffer must be a valid VkBuffer handle

  • VUID-vkCmdDrawIndirectByteCountEXT-commandBuffer-recording
    commandBuffer must be in the recording state

  • VUID-vkCmdDrawIndirectByteCountEXT-commandBuffer-cmdpool
    The VkCommandPool that commandBuffer was allocated from must support VK_QUEUE_GRAPHICS_BIT operations

  • VUID-vkCmdDrawIndirectByteCountEXT-renderpass
    This command must only be called inside of a render pass instance

  • VUID-vkCmdDrawIndirectByteCountEXT-suspended
    This command must not be called between suspended render pass instances

  • VUID-vkCmdDrawIndirectByteCountEXT-videocoding
    This command must only be called outside of a video coding scope

  • VUID-vkCmdDrawIndirectByteCountEXT-commonparent
    Both of commandBuffer, and counterBuffer must have been created, allocated, or retrieved from the same VkDevice

Host Synchronization

  • Host access to commandBuffer must be externally synchronized

  • Host access to the VkCommandPool that commandBuffer was allocated from must be externally synchronized

Command Properties
Command Buffer Levels Render Pass Scope Video Coding Scope Supported Queue Types Command Type

Primary
Secondary

Inside

Outside

VK_QUEUE_GRAPHICS_BIT

Action
Conditional Rendering

vkCmdDrawIndirectByteCountEXT is affected by conditional rendering

See Also

VK_EXT_transform_feedback, VkBuffer, VkCommandBuffer, VkDeviceSize

Document Notes

For more information, see the Vulkan Specification.

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.