clCreateImage

Creates a 1D image, 1D image buffer, 1D image array, 2D image, 2D image array or 3D image object.

cl_mem clCreateImage ( cl_context context,
  cl_mem_flags flags,
  const cl_image_format *image_format,
  const cl_image_desc *image_desc,
  void *host_ptr,
  cl_int *errcode_ret)

Parameters

context

A valid OpenCL context on which the image object is to be created.

flags

A bit-field that is used to specify allocation and usage information about the image memory object being created and is described in the table below.

For all image types except CL_MEM_OBJECT_IMAGE1D_BUFFER, if value specified for flags is 0, the default is used which is CL_MEM_READ_WRITE.

For CL_MEM_OBJECT_IMAGE1D_BUFFER image type, or an image created from another memory object (image or buffer), if the CL_MEM_READ_WRITE, CL_MEM_READ_ONLY or CL_MEM_WRITE_ONLY values are not specified in flags, they are inherited from the corresponding memory access qualifers associated with mem_object. The CL_MEM_USE_HOST_PTR, CL_MEM_ALLOC_HOST_PTR and CL_MEM_COPY_HOST_PTR values cannot be specified in flags but are inherited from the corresponding memory access qualifiers associated with mem_object. If CL_MEM_COPY_HOST_PTR is specified in the memory access qualifier values associated with mem_object it does not imply any additional copies when the image is created from mem_object. If the CL_MEM_HOST_WRITE_ONLY, CL_MEM_HOST_READ_ONLY or CL_MEM_HOST_NO_ACCESS values are not specified in flags, they are inherited from the corresponding memory access qualifiers associated with mem_object.

cl_mem_flags Description
CL_MEM_READ_WRITE This flag specifies that the memory object will be read and written by a kernel. This is the default.
CL_MEM_WRITE_ONLY

This flag specifies that the memory object will be written but not read by a kernel.

Reading from a buffer or image object created with CL_MEM_WRITE_ONLY inside a kernel is undefined.

CL_MEM_READ_WRITE and CL_MEM_WRITE_ONLY are mutually exclusive.

CL_MEM_READ_ONLY

This flag specifies that the memory object is a read-only memory object when used inside a kernel.

Writing to a buffer or image object created with CL_MEM_READ_ONLY inside a kernel is undefined.

CL_MEM_READ_WRITE or CL_MEM_WRITE_ONLY and CL_MEM_READ_ONLY are mutually exclusive.

CL_MEM_USE_HOST_PTR

This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to use memory referenced by host_ptr as the storage bits for the memory object.

OpenCL implementations are allowed to cache the buffer contents pointed to by host_ptr in device memory. This cached copy can be used when kernels are executed on a device.

The result of OpenCL commands that operate on multiple buffer objects created with the same host_ptr or overlapping host regions is considered to be undefined.

Refer to the description of the alignment rules for host_ptr for memory objects (buffer and images) created using CL_MEM_USE_HOST_PTR.

CL_MEM_ALLOC_HOST_PTR

This flag specifies that the application wants the OpenCL implementation to allocate memory from host accessible memory.

CL_MEM_ALLOC_HOST_PTR and CL_MEM_USE_HOST_PTR are mutually exclusive.

CL_MEM_COPY_HOST_PTR

This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to allocate memory for the memory object and copy the data from memory referenced by host_ptr.

CL_MEM_COPY_HOST_PTR and CL_MEM_USE_HOST_PTR are mutually exclusive.

CL_MEM_COPY_HOST_PTR can be used with CL_MEM_ALLOC_HOST_PTR to initialize the contents of the cl_mem object allocated using host-accessible (e.g. PCIe) memory.

CL_MEM_HOST_WRITE_ONLY

This flag specifies that the host will only write to the memory object (using OpenCL APIs that enqueue a write or a map for write). This can be used to optimize write access from the host (e.g. enable write-combined allocations for memory objects for devices that communicate with the host over a system bus such as PCIe).

CL_MEM_HOST_READ_ONLY

This flag specifies that the host will only read the memory object (using OpenCL APIs that enqueue a read or a map for read).

CL_MEM_HOST_WRITE_ONLY and CL_MEM_HOST_READ_ONLY are mutually exclusive.

CL_MEM_HOST_NO_ACCESS

This flag specifies that the host will not read or write the memory object.

CL_MEM_HOST_WRITE_ONLY or CL_MEM_HOST_READ_ONLY and CL_MEM_HOST_NO_ACCESS are mutually exclusive.

image_format

A pointer to a structure that describes format properties of the image to be allocated. See cl_image_format for a detailed description of the image format descriptor.

image_desc

A pointer to a structure that describes type and dimensions of the image to be allocated. See cl_image_desc for more information.

host_ptr

A pointer to the image data that may already be allocated by the application. Refer to table below for a description of how large the buffer that host_ptr points to must be.

Image Type Size of buffer that host_ptr points to
CL_MEM_OBJECT_IMAGE1D ≥ image_row_pitch
CL_MEM_OBJECT_IMAGE1D_BUFFER ≥ image_row_pitch
CL_MEM_OBJECT_IMAGE2D ≥ image_row_pitch * image_height
CL_MEM_OBJECT_IMAGE3D ≥ image_slice_pitch * image_depth
CL_MEM_OBJECT_IMAGE1D_ARRAY ≥ image_slice_pitch * image_array_size
CL_MEM_OBJECT_IMAGE2D_ARRAY ≥ image_slice_pitch * image_array_size

clCreateImage can be used to create a 2D image from a buffer object or a 2D image from another 2D image object.

A 2D image can be created from a buffer by specifying a buffer object in the image_desc->mem_object passed to clCreateImage for image_desc->image_type = CL_MEM_OBJECT_IMAGE2D. If image_desc->mem_object is created with CL_MEM_USE_HOST_PTR, the host_ptr specified to clCreateBuffer must be aligned to the minimum of the CL_DEVICE_IMAGE_BASE_ADDRESS_ALIGNMENT value for all devices in the context associated with image_desc->mem_object and that support images.

A 2D image can be created from another 2D image object by specifying an image object in the image_desc->mem_object passed to clCreateImage for image_desc->image_type = CL_MEM_OBJECT_IMAGE2D. This allows users to create a new image object that shares the image data store with mem_object but views the pixels in the image with a different channel order and channel type. The restrictions are:

(1) all the values specified in image_desc except for mem_object must match the image descriptor information associated with mem_object.

(2) the channel data type specified in image_format must match the channel data type associated with mem_object. The channel order values supported are:

image_channel_order specified in image_format image channel order of mem_object
CL_sBGRA CL_BGRA
CL_BGRA CL_sBGRA
CL_sRGBA CL_RGBA
CL_RGBA CL_sRGBA
CL_sRGB CL_RGB
CL_RGB CL_sRGB
CL_sRGBx CL_RGBx
CL_RGBx CL_sRGBx

This allows developers to create a sRGB view of the image from a linear RGB view or vice-versa i.e. the pixels stored in the image can be accessed aslinear RGB or sRGB values.

For a 3D image or 2D image array, the image data specified by host_ptr is stored as a linear sequence of adjacent 2D image slices or 2D images respectively. Each 2D image is a linear sequence of adjacent scanlines. Each scanline is a linear sequence of image elements.

For a 2D image, the image data specified by host_ptr is stored as a linear sequence of adjacent scanlines. Each scanline is a linear sequence of image elements.

For a 1D image array, the image data specified by host_ptr is stored as a linear sequence of adjacent 1D images respectively. Each 1D image or 1D image buffer is a single scanline which is a linear sequence of adjacent elements.

errcode_ret

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

If the cl_khr_mipmap_image extension is enabled, then a mip-mapped 1D image, 1D image array, 2D image, 2D image array or 3D image is created by specifying num_mip_levels to be a value > 1 in cl_image_desc passed to clCreateImage. The dimensions of a mip-mapped image can be a power of two or a non-power of two. Each successively smaller mipmap level is half the size of the previous level. If this half value is a fractional value, it is rounded down to the nearest integer.

Restrictions

The following restrictions apply when mip-mapped images are created with clCreateImage.

  • CL_MEM_USE_HOST_PTR or CL_MEM_COPY_HOST_PTR cannot be specified if a mipmapped image is created.
  • The host_ptr argument to clCreateImage must be a NULL value.
  • " Mip-mapped images cannot be created for CL_MEM_OBJECT_IMAGE1D_BUFFER images and multi-sampled (i.e. msaa) images.

Errors

clCreateImage returns a valid non-zero image object and errcode_ret is set to CL_SUCCESS if the image object is created successfully. Otherwise, it returns a NULL value with one of the following error values returned in errcode_ret:

  • CL_INVALID_CONTEXT if context is not a valid context.
  • CL_INVALID_VALUE if values specified in flags are not valid.
  • CL_INVALID_IMAGE_FORMAT_DESCRIPTOR if values specified in image_format are not valid or if image_format is NULL.
  • CL_INVALID_IMAGE_FORMAT_DESCRIPTOR if a 2D image is created from a buffer and the row pitch and base address alignment does not follow the rules described for creating a 2D image from a buffer.
  • CL_INVALID_IMAGE_FORMAT_DESCRIPTOR if a 2D image is created from a 2D image object and the rules described above are not followed.
  • CL_INVALID_IMAGE_DESCRIPTOR if values specified in image_desc are not valid or if image_desc is NULL.
  • CL_INVALID_IMAGE_SIZE if image dimensions specified in image_desc exceed the maximum image dimensions described in the table of allowed values for param_name for clGetDeviceInfo for all devices in context.
  • CL_INVALID_HOST_PTR if host_ptr is NULL and CL_MEM_USE_HOST_PTR or CL_MEM_COPY_HOST_PTR are set in flags or if host_ptr is not NULL but CL_MEM_COPY_HOST_PTR or CL_MEM_USE_HOST_PTR are not set in flags.
  • CL_INVALID_VALUE if an image buffer is being created and the buffer object was created with CL_MEM_WRITE_ONLY and flags specifies CL_MEM_READ_WRITE or CL_MEM_READ_ONLY, or if the buffer object was created with CL_MEM_READ_ONLY and flags specifies CL_MEM_READ_WRITE or CL_MEM_WRITE_ONLY, or if flags specifies CL_MEM_USE_HOST_PTR or CL_MEM_ALLOC_HOST_PTR or CL_MEM_COPY_HOST_PTR.
  • CL_INVALID_VALUE if an image buffer is being created or an image is being created from another memory object (image or buffer) and the mem_object object was created with CL_MEM_HOST_WRITE_ONLY and flags specifies CL_MEM_HOST_READ_ONLY, or if mem_object was created with CL_MEM_HOST_READ_ONLY and flags specifies CL_MEM_HOST_WRITE_ONLY, or if mem_object was created with CL_MEM_HOST_NO_ACCESS and flags specifies CL_MEM_HOST_READ_ONLY or CL_MEM_HOST_WRITE_ONLY.
  • CL_IMAGE_FORMAT_NOT_SUPPORTED if the image_format is not supported.
  • CL_MEM_OBJECT_ALLOCATION_FAILURE if there is a failure to allocate memory for image object.
  • CL_INVALID_OPERATION if there are no devices in context that support images (i.e. CL_DEVICE_IMAGE_SUPPORT (specified in the table of OpenCL Device Queries for clGetDeviceInfo) is CL_FALSE).
  • 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

cl_image_desc, cl_image_format, Cardinality Diagram, cl_khr_mipmap_image

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