clEnqueueReadImage - Enqueue commands to read from an image or image array object to host memory.

Authors

TheKhronosGroup

Copyright

       Copyright © 2007-2011 The Khronos Group Inc.
       Permission is hereby granted, free of charge, to any person obtaining a copy of this software and/or
       associated documentation files (the "Materials"), to deal in the Materials without restriction, including
       without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
       copies of the Materials, and to permit persons to whom the Materials are furnished to do so, subject to
       the condition that this copyright notice and permission notice shall be included in all copies or
       substantial portions of the Materials.

Errors

clEnqueueReadImage 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 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 read 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_INVALID_IMAGE_FORMAT 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 in the table of allowed values for param_name for
clGetDeviceInfo(3clc) is CL_FALSE).

• CL_INVALID_OPERATION if clEnqueueReadImage is called on image which has been created with
CL_MEM_HOST_WRITE_ONLY or CL_MEM_HOST_NO_ACCESS.RE

• 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_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.

Name

       clEnqueueReadImage - Enqueue commands to read from an image or image array object to host memory.

       cl_intclEnqueueReadImage(cl_command_queuecommand_queue,cl_memimage,cl_boolblocking_read,constsize_t*origin,constsize_t*region,size_trow_pitch,size_tslice_pitch,void*ptr,cl_uintnum_events_in_wait_list,constcl_event*event_wait_list,cl_event*event);

Notes

        1. OpenCL Specification
           page 98, section 5.3.3 - Reading, Writing and Copying Image Objects

The Khronos Group                                  11/18/2024                           CLENQUEUEREADIMAGE(3clc)

Parameters

command_queue
Refers to the command-queue in which the read 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_read
Indicates if the read operations are blocking or non-blocking.

If blocking_read is CL_TRUE i.e. the read command is blocking, clEnqueueReadImage 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. map operation is non-blocking, clEnqueueReadImage 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 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.

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.

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 row_pitch is set to 0, the appropriate row pitch is calculated based on the size of
each element in bytes multiplied by width.

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 read. This must be 0 if image is a 1D or 2D image. This value must be greater than or equal to
row_pitch * height. If 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 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.