NAME¶
clEnqueueReadImage - Enqueue commands to read from an image or
image array object to host memory.
cl_int
clEnqueueReadImage(cl_command_queue command_queue,
cl_mem image,
cl_bool blocking_read,
const size_t *origin,
const size_t *region,
size_t row_pitch,
size_t 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 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.
NOTES¶
Calling clEnqueueReadImage to read 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 read is created with CL_MEM_USE_HOST_PTR, must
meet the following requirements in order to avoid undefined behavior:
• All commands that use this image object have
finished execution before the read command begins execution.
• The row_pitch and slice_pitch
argument values in clEnqueueReadImage 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 read command has finished execution.
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.
SPECIFICATION¶
OpenCL Specification[1]
SEE ALSO¶
clEnqueueWriteImage(3clc),
clEnqueueCopyImage(3clc)
AUTHORS¶
The Khronos Group
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.
NOTES¶
- 1.
- OpenCL Specification
page 98, section 5.3.3 - Reading, Writing and Copying
Image Objects
