Current File : //usr/include/OpenEXR/openexr_context.h
/*
** SPDX-License-Identifier: BSD-3-Clause
** Copyright Contributors to the OpenEXR Project.
*/
#ifndef OPENEXR_CONTEXT_H
#define OPENEXR_CONTEXT_H
#include "openexr_errors.h"
#include "openexr_base.h"
#include <stddef.h>
#include <stdint.h>
#ifdef __cplusplus
extern "C" {
#endif
/**
* @defgroup Context Context related definitions
*
* A context is a single instance of an OpenEXR file or stream. Beyond
* a particular file or stream handle, it also has separate controls
* for error handling and memory allocation. This is done to enable
* encoding or decoding on mixed hardware.
*
* @{
*/
/** Opaque context handle
*
* The implementation of this is partly opaque to provide better
* version portability, and all accesses to relevant data should
* happen using provided functions. This handle serves as a container
* and identifier for all the metadata and parts associated with a
* file and/or stream
*/
typedef struct _priv_exr_context_t* exr_context_t;
typedef const struct _priv_exr_context_t* exr_const_context_t;
/**
* @defgroup ContextFunctions OpenEXR Context Stream / File Functions
*
* @brief These are a group of function interfaces used to customize
* the error handling, memory allocations, or I/O behavior of an
* OpenEXR context.
*
* @{
*/
/** @brief Stream error notifier
*
* This function pointer is provided to the stream functions by the
* library such that they can provide a nice error message to the
* user during stream operations.
*/
typedef exr_result_t (*exr_stream_error_func_ptr_t) (
exr_const_context_t ctxt, exr_result_t code, const char* fmt, ...)
EXR_PRINTF_FUNC_ATTRIBUTE;
/** @brief Error callback function
*
* Because a file can be read from using many threads at once, it is
* difficult to store an error message for later retrieval. As such,
* when a file is constructed, a callback function can be provided
* which delivers an error message for the calling application to
* handle. This will then be delivered on the same thread causing the
* error.
*/
typedef void (*exr_error_handler_cb_t) (
exr_const_context_t ctxt, exr_result_t code, const char* msg);
/** Destroy custom stream function pointer
*
* Generic callback to clean up user data for custom streams.
* This is called when the file is closed and expected not to
* error
*
* @param failed - indicates the write operation failed, the
* implementor may wish to cleanup temporary
* files
*/
typedef void (*exr_destroy_stream_func_ptr_t) (
exr_const_context_t ctxt, void* userdata, int failed);
/** Query stream size function pointer
*
* Used to query the size of the file, or amount of data representing
* the openexr file in the data stream.
*
* This is used to validate requests against the file. If the size is
* unavailable, return -1, which will disable these validation steps
* for this file, although appropriate memory safeguards must be in
* place in the calling application.
*/
typedef int64_t (*exr_query_size_func_ptr_t) (
exr_const_context_t ctxt, void* userdata);
/** @brief Read custom function pointer
*
* Used to read data from a custom output. Expects similar semantics to
* pread or ReadFile with overlapped data under win32
*
* It is required that this provides thread-safe concurrent access to
* the same file. If the stream / input layer you are providing does
* not have this guarantee, your are responsible for providing
* appropriate serialization of requests.
*
* A file should be expected to be accessed in the following pattern:
* - upon open, the header and part information attributes will be read
* - upon the first image read request, the offset tables will be read
* multiple threads accessing this concurrently may actually read
* these values at the same time
* - chunks can then be read in any order as preferred by the
* application
*
* While this should mean that the header will be read in 'stream'
* order (no seeks required), no guarantee is made beyond that to
* retrieve image / deep data in order. So if the backing file is
* truly a stream, it is up to the provider to implement appropriate
* caching of data to give the appearance of being able to seek / read
* atomically.
*/
typedef int64_t (*exr_read_func_ptr_t) (
exr_const_context_t ctxt,
void* userdata,
void* buffer,
uint64_t sz,
uint64_t offset,
exr_stream_error_func_ptr_t error_cb);
/** Write custom function pointer
*
* Used to write data to a custom output. Expects similar semantics to
* pwrite or WriteFile with overlapped data under win32
*
* It is required that this provides thread-safe concurrent access to
* the same file. While it is unlikely that multiple threads will
* be used to write data for compressed forms, it is possible.
*
* A file should be expected to be accessed in the following pattern:
* - upon open, the header and part information attributes is constructed
*
* - when the write_header routine is called, the header becomes immutable
* and is written to the file. This computes the space to store the chunk
* offsets, but does not yet write the values
*
* - Image chunks are written to the file, and appear in the order
* they are written, not in the ordering that is required by the
* chunk offset table (unless written in that order). This may vary
* slightly if the size of the chunks is not directly known and
* tight packing of data is necessary
*
* - at file close, the chunk offset tables are written to the file
*/
typedef int64_t (*exr_write_func_ptr_t) (
exr_const_context_t ctxt,
void* userdata,
const void* buffer,
uint64_t sz,
uint64_t offset,
exr_stream_error_func_ptr_t error_cb);
/** @brief struct used to pass function pointers into the context
* initialization routines.
*
* This partly exists to avoid the chicken and egg issue around creating the storage needed for the context on systems which want to override the malloc / free routines.
*
* However, it also serves to make a tidier / simpler set of functions
* to create and start processing exr files.
*
* The size member is required for version portability
*
* It can be initialized using \ref EXR_DEFAULT_CONTEXT_INITIALIZER
*
* \code{.c}
* exr_context_initializer_t myctxtinit = DEFAULT_CONTEXT_INITIALIZER;
* myctxtinit.error_cb = &my_super_cool_error_callback_function;
* ...
* \endcode
*
*/
typedef struct _exr_context_initializer
{
/** @brief size member to tag initializer for version stability.
*
* This should be initialized to the size of the current
* structure. This allows EXR to add functions or other
* initializers in the future, and retain version compatibility
*/
size_t size;
/** @brief Error callback function pointer
*
* The error callback is allowed to be null, and will use a default print which outputs to stderr
*
* @sa exr_error_handler_cb_t
*/
exr_error_handler_cb_t error_handler_fn;
/** custom allocator, if null, will use malloc. @sa exr_memory_allocation_func_t */
exr_memory_allocation_func_t alloc_fn;
/** custom deallocator, if null, will use free. @sa exr_memory_free_func_t */
exr_memory_free_func_t free_fn;
/** passed to custom read, size, write, destroy functions below. Up to user to manage this pointer */
void* user_data;
/** @brief custom read routine.
*
* This is only used during read or update contexts. If this is
* provided, it is expected that the caller has previously made
* the stream available, and placed whatever stream / file data
* into \ref user_data above.
*
* If this is NULL, and the context requested is for reading an
* exr file, an internal implementation is provided for reading
* from normal filesystem files, and the filename provided is
* attempted to be opened as such.
*
* Expected to be NULL for a write-only operation, but is ignored
* if it is provided.
*
* For update contexts, both read and write functions must be
* provided if either is.
*
* @sa exr_read_func_ptr_t
*/
exr_read_func_ptr_t read_fn;
/** @brief custom size query routine.
*
* Used to provide validation when reading header values. If this
* is not provided, but a custom read routine is provided, this
* will disable some of the validation checks when parsing the
* image header.
*
* Expected to be NULL for a write-only operation, but is ignored
* if it is provided.
*
* @sa exr_query_size_func_ptr_t
*/
exr_query_size_func_ptr_t size_fn;
/** @brief custom write routine.
*
* This is only used during write or update contexts. If this is
* provided, it is expected that the caller has previously made
* the stream available, and placed whatever stream / file data
* into \ref user_data above.
*
* If this is NULL, and the context requested is for writing an
* exr file, an internal implementation is provided for reading
* from normal filesystem files, and the filename provided is
* attempted to be opened as such.
*
* For update contexts, both read and write functions must be
* provided if either is.
*
* @sa exr_write_func_ptr_t
*/
exr_write_func_ptr_t write_fn;
/** @brief optional function to destroy the user data block of a custom stream
*
* Allows one to free any user allocated data, and close any handles.
*
* @sa exr_destroy_stream_func_ptr_t
* */
exr_destroy_stream_func_ptr_t destroy_fn;
/** initializes a field specifying what the maximum image width
* allowed by the context is. See \ref exr_set_default_maximum_image_size to
* understand how this interacts with global defaults */
int max_image_width;
/** initializes a field specifying what the maximum image height
* allowed by the context is. See \ref exr_set_default_maximum_image_size to
* understand how this interacts with global defaults */
int max_image_height;
/** initializes a field specifying what the maximum tile width
* allowed by the context is. See \ref exr_set_default_maximum_tile_size to
* understand how this interacts with global defaults */
int max_tile_width;
/** initializes a field specifying what the maximum tile height
* allowed by the context is. See \ref exr_set_default_maximum_tile_size to
* understand how this interacts with global defaults */
int max_tile_height;
} exr_context_initializer_t;
/** @brief simple macro to initialize the context initializer with default values */
#define EXR_DEFAULT_CONTEXT_INITIALIZER \
{ \
sizeof (exr_context_initializer_t), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 \
}
/** @} */ /* context function pointer declarations */
/** @brief Check the magic number of the file and report
* `EXR_ERR_SUCCESS` if the file appears to be a valid file (or at least
* has the correct magic number and can be read)
*/
EXR_EXPORT exr_result_t exr_test_file_header (
const char* filename,
const exr_context_initializer_t* ctxtdata);
/** @brief Close and free any internally allocated memory,
* calling any provided destroy function for custom streams
*
* If the file was opened for write, first save the chunk offsets
* or any other unwritten data.
*/
EXR_EXPORT exr_result_t exr_finish (exr_context_t* ctxt);
/** @brief Create and initialize a read-only exr read context
*
* If a custom read function is provided, the filename is for
* informational purposes only, the system assumes the user has
* previously opened a stream, file, or whatever and placed relevant
* data in userdata to access that.
*
* One notable attribute of the context is that once it has been
* created and returned a successful code, it has parsed all the
* header data. This is done as one step such that it is easier to
* provide a safe context for multiple threads to request data from
* the same context concurrently.
*
* Once finished reading data, use \ref exr_finish to clean up
* the context.
*
* If you have custom I/O requirements, see the initializer context
* documentation \ref exr_context_initializer_t. The @p ctxtdata parameter
* is optional, if `NULL`, default values will be used.
*/
EXR_EXPORT exr_result_t exr_start_read (
exr_context_t* ctxt,
const char* filename,
const exr_context_initializer_t* ctxtdata);
/** @brief enum describing how default files are handled during write */
enum exr_default_write_mode
{
EXR_WRITE_FILE_DIRECTLY =
0, /**< overwrites filename provided directly, deleted upon error */
EXR_INTERMEDIATE_TEMP_FILE =
1 /**< creates a temporary file, renaming it upon successful write, leaving original upon error */
};
/** @brief Creates and initializes a write-only context.
*
* If a custom write function is provided, the filename is for
* informational purposes only, and the @p default_mode parameter will be
* ignored. As such, the system assumes the user has previously opened
* a stream, file, or whatever and placed relevant data in userdata to
* access that.
*
* Multi-Threading: To avoid issues with creating multi-part EXR
* files, the library approaches writing as a multi-step process, so
* the same concurrent guarantees can not be made for writing a
* file. The steps are:
*
* 1. Context creation (this function)
*
* 2. Part definition (required attributes and additional metadata)
*
* 3. Transition to writing data (this "commits" the part definitions,
* any changes requested after will result in an error)
*
* 4. Write part data in sequential order of parts ( part 0->(N-1) ).
*
* 5. Within each part, multiple threads can be encoding and writing
* data concurrently. For some EXR part definitions, this may be able
* to write data concurrently when it can predict the chunk sizes, or
* data is allowed to be padded. For others, it may need to
* temporarily cache chunks until the data is received to flush in
* order. The concurrency around this is handled by the library
*
* 6. Once finished writing data, use \ref exr_finish to clean
* up the context, which will flush any unwritten data such as the
* final chunk offset tables, and handle the temporary file flags.
*
* If you have custom I/O requirements, see the initializer context
* documentation \ref exr_context_initializer_t. The @p ctxtdata
* parameter is optional, if NULL, default values will be used.
*/
EXR_EXPORT exr_result_t exr_start_write (
exr_context_t* ctxt,
const char* filename,
enum exr_default_write_mode default_mode,
const exr_context_initializer_t* ctxtdata);
/** @brief Creates a new context for updating an exr file in place
*
* This is a custom mode that allows one to modify the value of a
* metadata entry, although not to change the size of the header, or
* any of the image data.
*
* If you have custom I/O requirements, see the initializer context
* documentation \ref exr_context_initializer_t. The @p ctxtdata parameter
* is optional, if NULL, default values will be used.
*/
EXR_EXPORT exr_result_t exr_start_inplace_header_update (
exr_context_t* ctxt,
const char* filename,
const exr_context_initializer_t* ctxtdata);
/** @brief Retrieve the file name the context is for as provided
* during the start routine.
*
* Do not free the resulting string.
*/
EXR_EXPORT exr_result_t
exr_get_file_name (exr_const_context_t ctxt, const char** name);
/** @brief Query the user data the context was constructed with. This
* is perhaps useful in the error handler callback to jump back into
* an object the user controls.
*/
EXR_EXPORT exr_result_t
exr_get_user_data (exr_const_context_t ctxt, void** userdata);
/** Any opaque attribute data entry of the specified type is tagged
* with these functions enabling downstream users to unpack (or pack)
* the data.
*
* The library handles the memory packed data internally, but the
* handler is expected to allocate and manage memory for the
* *unpacked* buffer (the library will call the destroy function).
*
* NB: the pack function will be called twice (unless there is a
* memory failure), the first with a NULL buffer, requesting the
* maximum size (or exact size if known) for the packed buffer, then
* the second to fill the output packed buffer, at which point the
* size can be re-updated to have the final, precise size to put into
* the file.
*/
EXR_EXPORT exr_result_t exr_register_attr_type_handler (
exr_context_t ctxt,
const char* type,
exr_result_t (*unpack_func_ptr) (
exr_context_t ctxt,
const void* data,
int32_t attrsize,
int32_t* outsize,
void** outbuffer),
exr_result_t (*pack_func_ptr) (
exr_context_t ctxt,
const void* data,
int32_t datasize,
int32_t* outsize,
void* outbuffer),
void (*destroy_unpacked_func_ptr) (
exr_context_t ctxt, void* data, int32_t datasize));
/** @brief Enable long name support in the output context */
EXR_EXPORT exr_result_t
exr_set_longname_support (exr_context_t ctxt, int onoff);
/** @brief Write the header data
*
* Opening a new output file has a small initialization state problem
* compared to opening for read / update: we need to enable the user
* to specify an arbitrary set of metadata across an arbitrary number
* of parts. To avoid having to create the list of parts and entire
* metadata up front, prior to calling the above \ref exr_start_write,
* allow the data to be set, then once this is called, it switches
* into a mode where the library assumes the data is now valid.
*
* It will recompute the number of chunks that will be written, and
* reset the chunk offsets. If you modify file attributes or part
* information after a call to this, it will error.
*/
EXR_EXPORT exr_result_t exr_write_header (exr_context_t ctxt);
/** @} */
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* OPENEXR_CONTEXT_H */
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