C Specification

To enqueue a command to map a region in the image object given by image into the host address space and returns a pointer to this mapped region, call the function

void* clEnqueueMapImage(
    cl_command_queue command_queue,
    cl_mem image,
    cl_bool blocking_map,
    cl_map_flags map_flags,
    const size_t* origin,
    const size_t* region,
    size_t* image_row_pitch,
    size_t* image_slice_pitch,
    cl_uint num_events_in_wait_list,
    const cl_event* event_wait_list,
    cl_event* event,
    cl_int* errcode_ret);

Parameters

  • command_queue must be a valid host command-queue.

  • image is a valid image object. The OpenCL context associated with command_queue and image must be the same.

  • blocking_map indicates if the map operation is blocking or non-blocking.

  • map_flags is a bit-field and is described in the Memory Map Flags table.

  • 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 2D 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.

  • image_row_pitch returns the scan-line pitch in bytes for the mapped region. This must be a non-NULL value.

  • image_slice_pitch returns the size in bytes of each 2D slice of a 3D image or the size of each 1D or 2D image in a 1D or 2D image array for the mapped region. For a 1D and 2D image, zero is returned if this argument is not NULL. For a 3D image, 1D and 2D image array, image_slice_pitch must be a non-NULL value.

  • event_wait_list and num_events_in_wait_list specify events that need to complete before clEnqueueMapImage can be executed. If event_wait_list is NULL, then clEnqueueMapImage 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 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.

  • errcode_ret will return an appropriate error code. If errcode_ret is NULL, no error code is returned.

Description

If blocking_map is CL_​TRUE, clEnqueueMapImage does not return until the specified region in image is mapped into the host address space and the application can access the contents of the mapped region using the pointer returned by clEnqueueMapImage.

If blocking_map is CL_​FALSE i.e. map operation is non-blocking, the pointer to the mapped region returned by clEnqueueMapImage cannot be used until the map command has completed. The event argument returns an event object which can be used to query the execution status of the map command. When the map command is completed, the application can access the contents of the mapped region using the pointer returned by clEnqueueMapImage.

clEnqueueMapImage will return a pointer to the mapped region. The errcode_ret is set to CL_​SUCCESS.

A NULL pointer is returned otherwise with one of the following error values returned in errcode_ret:

  • CL_​INVALID_​COMMAND_​QUEUE if command_queue is not a valid host command-queue.

  • CL_​INVALID_​CONTEXT if context associated with command_queue and image are not the same or if 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 region being mapped given by (origin, origin+region) is out of bounds or if values specified in map_flags are not valid.

  • CL_​INVALID_​VALUE if values in origin and region do not follow rules described in the argument description for origin and region.

  • CL_​INVALID_​VALUE if image_row_pitch is NULL.

  • CL_​INVALID_​VALUE if image is a 3D image, 1D or 2D image array object and image_slice_pitch is NULL.

  • 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_​MAP_​FAILURE if there is a failure to map the requested region into the host address space. This error cannot occur for image objects created with CL_​MEM_​USE_​HOST_​PTR or CL_​MEM_​ALLOC_​HOST_​PTR.

  • CL_​EXEC_​STATUS_​ERROR_​FOR_​EVENTS_​IN_​WAIT_​LIST if the map operation is blocking and the execution status of any of the events in event_wait_list is a negative integer value. This error code is missing before version 1.1.

  • 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 in the Device Queries table is CL_​FALSE).

  • CL_​INVALID_​OPERATION if image has been created with CL_​MEM_​HOST_​WRITE_​ONLY or CL_​MEM_​HOST_​NO_​ACCESS and CL_​MAP_​READ is set in map_flags or if image has been created with CL_​MEM_​HOST_​READ_​ONLY or CL_​MEM_​HOST_​NO_​ACCESS and CL_​MAP_​WRITE or CL_​MAP_​WRITE_​INVALIDATE_​REGION is set in map_flags.

  • 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.

  • CL_​INVALID_​OPERATION if mapping would lead to overlapping regions being mapped for writing.

The pointer returned maps a 1D, 2D or 3D region starting at origin and is at least region[0] pixels in size for a 1D image, 1D image buffer or 1D image array, (image_row_pitch × region[1]) pixels in size for a 2D image or 2D image array, and (image_slice_pitch × region[2]) pixels in size for a 3D image. The result of a memory access outside this region is undefined.

If the image object is created with CL_​MEM_​USE_​HOST_​PTR set in mem_flags, the following will be true:

  • The host_ptr specified in clCreateImage, clCreateImage2D or clCreateImage3D is guaranteed to contain the latest bits in the region being mapped when the clEnqueueMapImage command has completed.

  • The pointer value returned by clEnqueueMapImage will be derived from the host_ptr specified when the image object is created.

Mapped image objects are unmapped using clEnqueueUnmapMemObject. This is described in Unmapping Mapped Memory Objects.

See Also

Document Notes

For more information, see the OpenCL Specification

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

Copyright (c) 2014-2020 Khronos Group. This work is licensed under a Creative Commons Attribution 4.0 International License.