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clEnqueueWriteImage.adoc

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clEnqueueWriteImage

Enqueues a command to write to an image or image array object from host memory.

cl_int clEnqueueWriteImage(cl_command_queue command_queue,
                           cl_mem image,
                           cl_bool blocking_write,
                           const size_t *origin,
                           const size_t *region,
                           size_t input_row_pitch,
                           size_t input_slice_pitch,
                           const void * ptr,
                           cl_uint num_events_in_wait_list,
                           const cl_event *event_wait_list,
                           cl_event *event)

Parameters

command_queue

Refers to the host command-queue in which the write command will be queued. command_queue and image must be created with the same OpenCL context.

image

Refers to a valid image or image array object.

blocking_write

Indicates if the write operation is blocking or non-blocking.

If blocking_write is CL_TRUE the OpenCL implementation copies the data referred to by ptr and enqueues the write command in the command-queue. The memory pointed to by ptr can be reused by the application after the clEnqueueWriteImage call returns.

If blocking_write is CL_FALSE the OpenCL implementation will use ptr to perform a nonblocking write. As the write is non-blocking the implementation can return immediately. The memory pointed to by ptr cannot be reused by the application after the call returns. The event argument returns an event object which can be used to query the execution status of the write command. When the write command has completed, the memory pointed to by ptr can then be reused by the application.

origin

Defines the (x, y, z) offset in pixels in the 1D, 2D, or 3D image, the (x, y) offset and the image index in the image array or the (x) offset and the image index in the 1D image array. If image is a 2D image object, origin[2] must be 0. If image is a 1D image or 1D image buffer object, origin[1] and origin[2] must be 0. If image is a 1D image array object, origin[2] must be 0. If image is a 1D image array object, origin[1] describes the image index in the 1D image array. If image is a 2D image array object, origin[2] describes the image index in the 2D image array.

region

Defines the (width, height, depth) in pixels of the 1D, 2D or 3D rectangle, the (width, height) in pixels of the 2D rectangle and the number of images of a 2D image array or the (width) in pixels of the 1D rectangle and the number of images of a 1D image array. If image is a 2D image object, region[2] must be 1. If image is a 1D image or 1D image buffer object, region[1] and region[2] must be 1. If image is a 1D image array object, region[2] must be 1. The values in region cannot be 0.

input_row_pitch

The length of each row in bytes. This value must be greater than or equal to the element size in bytes * width. If input_row_pitch is set to 0, the appropriate row pitch is calculated based on the size of each element in bytes multiplied by width.

input_slice_pitch

Size in bytes of the 2D slice of the 3D region of a 3D image or each image of a 1D or 2D image array being written. This must be 0 if image is a 1D or 2D image. Otherwise this value must be greater than or equal to row_pitch * height. If input_slice_pitch is set to 0, the appropriate slice pitch is calculated based on the row_pitch * height.

ptr

The pointer to a buffer in host memory where image data is to be read from.

event_wait_list , 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 write 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 clEnqueueWriteImage to update the latest bits in a region of the image with the ptr argument value set to host_ptr + (origin[2] * image slice pitch + origin[1] * image row pitch + origin[0] * bytes per pixel), where host_ptr is a pointer to the memory region specified when the image 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 being written contains the latest bits when the enqueued write command begins execution.

  • The input_row_pitch and input_slice_pitch argument values in clEnqueueWriteImage must be set to the image row pitch and slice pitch.

  • The image object is not mapped.

  • The image object is not used by any command-queue until the write command has finished execution.

If the mipmap extensions are enabled with cl_khr_mipmap_image, calls to clEnqueueReadImage, clEnqueueWriteImage and clEnqueueMapImage can be used to read from or write to a specific mip-level of a mip-mapped image. If image argument is a 1D image, origin[1] specifies the mip-level to use. If image argument is a 1D image array, origin[2] specifies the mip-level to use. If image argument is a 2D image, origin[3] specifies the mip-level to use. If image argument is a 2D image array or a 3D image, origin[3] specifies the mip-level to use.

Errors

clEnqueueWriteImage return 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 host command-queue.

  • CL_INVALID_CONTEXT if the context associated with command_queue and image 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 image is not a valid image object.

  • CL_INVALID_VALUE if the region being written specified by origin and region is out of bounds or if ptr is a NULL value.

  • CL_INVALID_VALUE if values in origin and region do not follow rules described in the argument description for origin and region.

  • 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_INVALID_IMAGE_SIZE if image dimensions (image width, height, specified or compute row and/or slice pitch) for image are not supported by device associated with queue.

  • CL_IMAGE_FORMAT_NOT_SUPPORTED if image format (image channel order and data type) for image are not supported by device associated with queue.

  • CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for data store associated with image.

  • CL_INVALID_OPERATION if the device associated with command_queue does not support images (i.e. CL_DEVICE_IMAGE_SUPPORT specified the table of allowed values for param_name for clGetDeviceInfo is CL_FALSE).

  • CL_INVALID_OPERATION if clEnqueueWriteImage is called on image which has been created with CL_MEM_HOST_READ_ONLY or CL_MEM_HOST_NO_ACCESS.

  • CL_EXEC_STATUS_ERROR_FOR_EVENTS_IN_WAIT_LIST if the write operations are blocking and the execution status of any of the events in event_wait_list is a negative integer value.

  • 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.