vkCmdBeginTransformFeedbackEXT(3)

C Specification

Transform feedback for specific transform feedback buffers is made active by calling:

// Provided by VK_EXT_transform_feedback
void vkCmdBeginTransformFeedbackEXT(
    VkCommandBuffer                             commandBuffer,
    uint32_t                                    firstCounterBuffer,
    uint32_t                                    counterBufferCount,
    const VkBuffer*                             pCounterBuffers,
    const VkDeviceSize*                         pCounterBufferOffsets);

Parameters

commandBuffer is the command buffer into which the command is recorded.
firstCounterBuffer is the index of the first transform feedback buffer corresponding to pCounterBuffers[0] and pCounterBufferOffsets[0].
counterBufferCount is the size of the pCounterBuffers and pCounterBufferOffsets arrays.
pCounterBuffers is NULL or a pointer to an array of VkBuffer handles to counter buffers. Each buffer contains a 4 byte integer value representing the byte offset from the start of the corresponding transform feedback buffer from where to start capturing vertex data. If the byte offset stored to the counter buffer location was done using vkCmdEndTransformFeedbackEXT it can be used to resume transform feedback from the previous location. If pCounterBuffers is NULL, then transform feedback will start capturing vertex data to byte offset zero in all bound transform feedback buffers. For each element of pCounterBuffers that is VK_NULL_HANDLE, transform feedback will start capturing vertex data to byte zero in the corresponding bound transform feedback buffer.
pCounterBufferOffsets is NULL or a pointer to an array of VkDeviceSize values specifying offsets within each of the pCounterBuffers where the counter values were previously written. The location in each counter buffer at these offsets must be large enough to contain 4 bytes of data. This data is the number of bytes captured by the previous transform feedback to this buffer. If pCounterBufferOffsets is NULL, then it is assumed the offsets are zero.

Description

The active transform feedback buffers will capture primitives emitted from the corresponding XfbBuffer in the bound graphics pipeline. Any XfbBuffer emitted that does not output to an active transform feedback buffer will not be captured.

Valid Usage

VUID-vkCmdBeginTransformFeedbackEXT-transformFeedback-02366
VkPhysicalDeviceTransformFeedbackFeaturesEXT::transformFeedback must be enabled
VUID-vkCmdBeginTransformFeedbackEXT-None-02367
Transform feedback must not be active
VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02368
firstCounterBuffer must be less than VkPhysicalDeviceTransformFeedbackPropertiesEXT::maxTransformFeedbackBuffers
VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02369
The sum of firstCounterBuffer and counterBufferCount must be less than or equal to VkPhysicalDeviceTransformFeedbackPropertiesEXT::maxTransformFeedbackBuffers
VUID-vkCmdBeginTransformFeedbackEXT-counterBufferCount-02607
If counterBufferCount is not 0, and pCounterBuffers is not NULL, pCounterBuffers must be a valid pointer to an array of counterBufferCount VkBuffer handles that are either valid or VK_NULL_HANDLE
VUID-vkCmdBeginTransformFeedbackEXT-pCounterBufferOffsets-02370
For each buffer handle in the array, if it is not VK_NULL_HANDLE it must reference a buffer large enough to hold 4 bytes at the corresponding offset from the pCounterBufferOffsets array
VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffer-02371
If pCounterBuffer is NULL, then pCounterBufferOffsets must also be NULL
VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffers-02372
For each buffer handle in the pCounterBuffers array that is not VK_NULL_HANDLE it must have been created with a usage value containing VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_COUNTER_BUFFER_BIT_EXT
VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-09630
The sum of firstCounterBuffer and counterBufferCount must be less than or equal to the number of transform feedback buffers currently bound by vkCmdBindTransformFeedbackBuffersEXT
VUID-vkCmdBeginTransformFeedbackEXT-None-06233
If the shaderObject feature is not enabled, a valid graphics pipeline must be bound to VK_PIPELINE_BIND_POINT_GRAPHICS
VUID-vkCmdBeginTransformFeedbackEXT-None-04128
The last pre-rasterization shader stage of the bound graphics pipeline must have been declared with the Xfb execution mode
VUID-vkCmdBeginTransformFeedbackEXT-None-02373
Transform feedback must not be made active in a render pass instance with multiview enabled

Valid Usage (Implicit)

VUID-vkCmdBeginTransformFeedbackEXT-commandBuffer-parameter
commandBuffer must be a valid VkCommandBuffer handle
VUID-vkCmdBeginTransformFeedbackEXT-pCounterBufferOffsets-parameter
If counterBufferCount is not 0, and pCounterBufferOffsets is not NULL, pCounterBufferOffsets must be a valid pointer to an array of counterBufferCount VkDeviceSize values
VUID-vkCmdBeginTransformFeedbackEXT-commandBuffer-recording
commandBuffer must be in the recording state
VUID-vkCmdBeginTransformFeedbackEXT-commandBuffer-cmdpool
The VkCommandPool that commandBuffer was allocated from must support graphics operations
VUID-vkCmdBeginTransformFeedbackEXT-renderpass
This command must only be called inside of a render pass instance
VUID-vkCmdBeginTransformFeedbackEXT-videocoding
This command must only be called outside of a video coding scope
VUID-vkCmdBeginTransformFeedbackEXT-commonparent
Both of commandBuffer, and the elements of pCounterBuffers that are valid handles of non-ignored parameters 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