clEnqueueReadBufferRect
clEnqueueReadBufferRect
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clEnqueueReadBufferRect Enqueue commands to read from a rectangular region from a buffer object to host memory.

##

cl_int `clEnqueueReadBufferRect` cl_command_queue command_queue cl_mem buffer cl_bool blocking_read const size_t *buffer_origin const size_t *host_origin const size_t *region size_t buffer_row_pitch size_t buffer_slice_pitch size_t host_row_pitch size_t host_slice_pitch void *ptr cl_uint num_events_in_wait_list const cl_event *event_wait_list cl_event *event

## Parameters

`command_queue`

  Refers to the command-queue in which the read command will be queued. `command_queue` and `buffer` must be created with the same OpenCL context.

`buffer`

  Refers to a valid buffer object.

`blocking_read`

  Indicates if the read operations are `blocking` or non-blocking.

  If `blocking_read` is `CL_TRUE` i.e. the read command is blocking, `clEnqueueReadBufferRect` does not return until the buffer data has been read and copied into memory pointed to by `ptr`.

  If `blocking_read` is `CL_FALSE` i.e. the read command is `non-blocking`, `clEnqueueReadBufferRect` queues a non-blocking read command and returns. The contents of the buffer that `ptr` points to cannot be used until the read command has completed. The `event` argument argument returns an event object which can be used to query the execution status of the read command. When the read command has completed, the contents of the buffer that `ptr` points to can be used by the application.

`buffer_origin`

  The (x, y, z) offset in the memory region associated with `buffer`. For a 2D rectangle region, the `z` value given by `buffer_origin`[2] should be 0. The offset in bytes is computed as `buffer_origin`[2] * `buffer_slice_pitch` + `buffer_origin`[1] * `buffer_row_pitch` + `buffer_origin`[0].

`host_origin`

  The (x, y, z) offset in the memory region pointed to by `ptr`. For a 2D rectangle region, the `z` value given by `host_origin`[2] should be 0. The offset in bytes is computed as `host_origin`[2] * `host_slice_pitch` + `host_origin`[1] * `host_row_pitch` + `host_origin`[0].

`region`

  The (width, height, depth) in bytes of the 2D or 3D rectangle being read or written. For a 2D rectangle copy, the `depth` value given by `region`[2] should be 1.

`buffer_row_pitch`

  The length of each row in bytes to be used for the memory region associated with `buffer`. If `buffer_row_pitch` is 0, `buffer_row_pitch` is computed as `region`[0].

`buffer_slice_pitch`

  The length of each 2D slice in bytes to be used for the memory region associated with `buffer`. If `buffer_slice_pitch` is 0, `buffer_slice_pitch` is computed as `region`[1] * `buffer_row_pitch`.

`host_row_pitch`

  The length of each row in bytes to be used for the memory region pointed to by `ptr`. If `host_row_pitch` is 0, `host_row_pitch` is computed as `region`[0].

`host_slice_pitch`

  The length of each 2D slice in bytes to be used for the memory region pointed to by `ptr`. If `host_slice_pitch` is 0, `host_slice_pitch` is computed as `region`[1] * `host_row_pitch`.

`ptr`

  The pointer to buffer in host memory where data is to be read into.

`event_wait_list`
`num_events_in_wait_list`

  `event_wait_list` and `num_events_in_wait_list` specify events that need to complete before this particular command can be executed. If `event_wait_list` is NULL, then this particular command does not wait on any event to complete. If `event_wait_list` is NULL, `num_events_in_wait_list` must be 0. If `event_wait_list` is not NULL, the list of events pointed to by `event_wait_list` must be valid and `num_events_in_wait_list` must be greater than 0. The events specified in `event_wait_list` act as synchronization points. The context associated with events in `event_wait_list` and `command_queue` must be the same. The memory associated with `event_wait_list` can be reused or freed after the function returns.

`event`

  Returns an event object that identifies this particular read command and can be used to query or queue a wait for this particular command to complete. `event` can be NULL in which case it will not be possible for the application to query the status of this command or queue a wait for this command to complete. If the `event_wait_list` and the event arguments are not NULL, the `event` argument should not refer to an element of the `event_wait_list` array.

## Notes

Calling `clEnqueueReadBufferRect` to read a region of the buffer object with the `ptr` argument value set to `host_ptr` and `host_origin`, `buffer_origin` values are the same, where `host_ptr` is a pointer to the memory region specified when the buffer object being read is created with `CL_MEM_USE_HOST_PTR`, must meet the same requirements given for clEnqueueReadBuffer.

Calling `clEnqueueWriteBufferRect` to update the latest bits in a region of the buffer object with the `ptr` argument value set to `host_ptr` and `host_origin`, `buffer_origin` values are the same, where `host_ptr` is a pointer to the memory region specified when the buffer object being written is created with `CL_MEM_USE_HOST_PTR`, must meet the following requirements in order to avoid undefined behavior:

- The host memory region given by (`buffer_origin` `region`) contains the latest bits when the enqueued write command begins execution.
- The buffer object or memory objects created from this buffer object are not mapped.
- The buffer object or memory objects created from this buffer object are not used by any command-queue until the write command has finished execution.

## Errors

`clEnqueueReadBufferRect` returns CL_SUCCESS if the function is executed successfully. Otherwise, it returns one of the following errors:

- CL_INVALID_COMMAND_QUEUE if `command_queue` is not a valid command-queue.
- CL_INVALID_CONTEXT if the context associated with `command_queue` and `buffer` are not the same or if the context associated with `command_queue` and events in `event_wait_list` are not the same.
- CL_INVALID_MEM_OBJECT if `buffer` is not a valid buffer object.
- CL_INVALID_VALUE if the region being read specified by (`buffer_origin`, `region`, `buffer_row_pitch`, `buffer_slice_pitch`) is out of bounds.
- CL_INVALID_VALUE if `ptr` is a NULL value.
- CL_INVALID_VALUE if any `region` array element is 0.
- CL_INVALID_VALUE if `buffer_row_pitch` is not 0 and is less than `region`[0].
- CL_INVALID_VALUE if `host_row_pitch` is not 0 and is less than `region`[0].
- CL_INVALID_VALUE if `buffer_slice_pitch` is not 0 and is less than `region`[1] * `buffer_row_pitch` and not a multiple of `buffer_row_pitch`.
- CL_INVALID_VALUE if `host_slice_pitch` is not 0 and is less than `region`[1] * `host_row_pitch` and not a multiple of `host_row_pitch`.
- CL_INVALID_EVENT_WAIT_LIST if `event_wait_list` is NULL and `num_events_in_wait_list` > 0, or `event_wait_list` is not NULL and `num_events_in_wait_list` is 0, or if event objects in `event_wait_list` are not valid events.
- CL_MISALIGNED_SUB_BUFFER_OFFSET if `buffer` is a sub-buffer object and `offset` specified when the sub-buffer object is created is not aligned to `CL_DEVICE_MEM_BASE_ADDR_ALIGN` value for device associated with `queue`.
- CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST if the read and write operations are blocking and the execution status of any of the events in `event_wait_list` is a negative integer value.
- CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for data store associated with `buffer`.
- CL_INVALID_OPERATION if `clEnqueueReadBufferRect` is called on `buffer` which has been created with `CL_MEM_HOST_WRITE_ONLY` or `CL_MEM_HOST_NO_ACCESS`.
- CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
- CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

## Specification

OpenCL Specification

## Also see

clEnqueueCopyBuffer, clEnqueueCopyBufferRect, clEnqueueWriteBuffer, clEnqueueWriteBufferRect, clEnqueueReadBuffer

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