clEnqueueMapImage
clEnqueueMapImage
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clEnqueueMapImage Enqueues a command to map a region of an image object into the host address space and returns a pointer to this mapped region.

##

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 command-queue.

`image`

  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`.

  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`.

`map_flags`

  A bit-bield with the following supported values.

  cl_map_flags | Description
  --- | ---
  `CL_MAP_READ` | This flag specifies that the region being mapped in the memory object is being mapped for reading. The pointer returned by clEnqueueMapBuffer or `clEnqueueMapImage` is guaranteed to contain the latest bits in the region being mapped when the clEnqueueMapBuffer or `clEnqueueMapImage` command has completed
  `CL_MAP_WRITE` | This flag specifies that the region being mapped in the memory object is being mapped for writing. The pointer returned by clEnqueueMapBuffer or `clEnqueueMapImage` is guaranteed to contain the latest bits in the region being mapped when the clEnqueueMapBuffer or `clEnqueueMapImage` command has completed.
  `CL_MAP_WRITE_INVALIDATE_REGION` | This flag specifies that the region being mapped in the memory object is being mapped for writing. The contents of the region being mapped are to be discarded. This is typically the case when the region being mapped is overwritten by the host. This flag allows the implementation to no longer guarantee that the pointer returned by clEnqueueMapBuffer or `clEnqueueMapImage` contains the latest bits in the region being mapped which can be a significant performance enhancement. `CL_MAP_READ` or `CL_MAP_WRITE` and `CL_MAP_WRITE_INVALIDATE_REGION` are mutually exclusive.

`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.

`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 ,` `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 copy 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`

  Returns an appropriate error code. If `errcode_ret` is NULL, no error code is returned.

## Notes

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 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.

clEnqueueMapBuffer and `clEnqueueMapImage` increment the mapped count of the memory object. The initial mapped count value of a memory object is zero. Multiple calls to clEnqueueMapBuffer or `clEnqueueMapImage` on the same memory object will increment this mapped count by appropriate number of calls. `clEnqueueUnmapMemObject` decrements the mapped count of the memory object.

clEnqueueMapBuffer and `clEnqueueMapImage` act as synchronization points for a region of the buffer object being mapped.

## Errors

`clEnqueueMapImage` will return a pointer to the mapped region if the function is executed successfully. 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 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 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_INVALID_IMAGE_FORMAT 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.
- CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for data store associated with `buffer`.
- CL_INVALID_OPERATION if the device associated with `command_queue` does not support images (i.e. `CL_DEVICE_IMAGE_SUPPORT` specified in the table of OpenCL Device Queries for clGetDeviceInfo 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.

## Specification

OpenCL Specification

## Also see

clEnqueueMapBuffer, clEnqueueUnmapMemObject

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