vkCmdBeginTransformFeedbackEXT(3)

C Specification

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

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 an optional array of buffer handles to the counter buffers which contain 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 an optional array of 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

VkPhysicalDeviceTransformFeedbackFeaturesEXT::transformFeedback must be enabled
Transform feedback must not be active
firstCounterBuffer must be less than VkPhysicalDeviceTransformFeedbackPropertiesEXT::maxTransformFeedbackBuffers
The sum of firstCounterBuffer and counterBufferCount must be less than or equal to VkPhysicalDeviceTransformFeedbackPropertiesEXT::maxTransformFeedbackBuffers
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
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
If pCounterBuffer is NULL, then pCounterBufferOffsets must also be NULL
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
Transform feedback must not be made active in a render pass instance with multiview enabled

Valid Usage (Implicit)

commandBuffer must be a valid VkCommandBuffer handle
If counterBufferCount is not 0, and pCounterBufferOffsets is not NULL, pCounterBufferOffsets must be a valid pointer to an array of counterBufferCount VkDeviceSize values
commandBuffer must be in the recording state
The VkCommandPool that commandBuffer was allocated from must support graphics operations
This command must only be called inside of a render pass instance
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