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// Copyright 2021 The Wuffs Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// ---------------- Auxiliary - Image
namespace wuffs_aux {
struct DecodeImageResult {
DecodeImageResult(MemOwner&& pixbuf_mem_owner0,
wuffs_base__pixel_buffer pixbuf0,
std::string&& error_message0);
DecodeImageResult(std::string&& error_message0);
MemOwner pixbuf_mem_owner;
wuffs_base__pixel_buffer pixbuf;
std::string error_message;
// DecodeImageCallbacks are the callbacks given to DecodeImage. They are always
// called in this order:
// 1. SelectDecoder
// 2. HandleMetadata
// 3. SelectPixfmt
// 4. AllocPixbuf
// 5. AllocWorkbuf
// 6. Done
// It may return early - the third callback might not be invoked if the second
// one fails - but the final callback (Done) is always invoked.
class DecodeImageCallbacks {
// AllocPixbufResult holds a memory allocation (the result of malloc or new,
// a statically allocated pointer, etc), or an error message. The memory is
// de-allocated when mem_owner goes out of scope and is destroyed.
struct AllocPixbufResult {
AllocPixbufResult(MemOwner&& mem_owner0, wuffs_base__pixel_buffer pixbuf0);
AllocPixbufResult(std::string&& error_message0);
MemOwner mem_owner;
wuffs_base__pixel_buffer pixbuf;
std::string error_message;
// AllocWorkbufResult holds a memory allocation (the result of malloc or new,
// a statically allocated pointer, etc), or an error message. The memory is
// de-allocated when mem_owner goes out of scope and is destroyed.
struct AllocWorkbufResult {
AllocWorkbufResult(MemOwner&& mem_owner0, wuffs_base__slice_u8 workbuf0);
AllocWorkbufResult(std::string&& error_message0);
MemOwner mem_owner;
wuffs_base__slice_u8 workbuf;
std::string error_message;
virtual ~DecodeImageCallbacks();
// SelectDecoder returns the image decoder for the input data's file format.
// Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).
// Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],
// such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that Wuffs'
// standard library did not recognize the image format but if SelectDecoder
// was overridden, it may examine the input data's starting bytes and still
// provide its own image decoder, e.g. for an exotic image file format that's
// not in Wuffs' standard library. The prefix_etc fields have the same
// meaning as wuffs_base__magic_number_guess_fourcc arguments. SelectDecoder
// implementations should not modify prefix_data's contents.
// SelectDecoder might be called more than once, since some image file
// formats can wrap others. For example, a nominal BMP file can actually
// contain a JPEG or a PNG.
// The default SelectDecoder accepts the FOURCC codes listed below. For
// modular builds (i.e. when #define'ing WUFFS_CONFIG__MODULES), acceptance
// of the ETC file format is optional (for each value of ETC) and depends on
// the corresponding module to be enabled at compile time (i.e. #define'ing
virtual wuffs_base__image_decoder::unique_ptr //
SelectDecoder(uint32_t fourcc,
wuffs_base__slice_u8 prefix_data,
bool prefix_closed);
// HandleMetadata acknowledges image metadata. minfo.flavor will be one of:
// If it is ETC__METADATA_RAW_ETC then raw contains the metadata bytes. Those
// bytes should not be retained beyond the the HandleMetadata call.
// minfo.metadata__fourcc() will typically match one of the
// DecodeImageArgFlags bits. For example, if (REPORT_METADATA_CHRM |
// REPORT_METADATA_GAMA) was passed to DecodeImage then the metadata FourCC
// It returns an error message, or an empty string on success.
virtual std::string //
HandleMetadata(const wuffs_base__more_information& minfo,
wuffs_base__slice_u8 raw);
// SelectPixfmt returns the destination pixel format for AllocPixbuf. It
// should return wuffs_base__make_pixel_format(etc) called with one of:
// or return image_config.pixcfg.pixel_format(). The latter means to use the
// image file's natural pixel format. For example, GIF images' natural pixel
// format is an indexed one.
// Returning otherwise means failure (DecodeImage_UnsupportedPixelFormat).
// The default SelectPixfmt implementation returns
// wuffs_base__make_pixel_format(WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL) which
// is 4 bytes per pixel (8 bits per channel × 4 channels).
virtual wuffs_base__pixel_format //
SelectPixfmt(const wuffs_base__image_config& image_config);
// AllocPixbuf allocates the pixel buffer.
// allow_uninitialized_memory will be true if a valid background_color was
// passed to DecodeImage, since the pixel buffer's contents will be
// overwritten with that color after AllocPixbuf returns.
// The default AllocPixbuf implementation allocates either uninitialized or
// zeroed memory. Zeroed memory typically corresponds to filling with opaque
// black or transparent black, depending on the pixel format.
virtual AllocPixbufResult //
AllocPixbuf(const wuffs_base__image_config& image_config,
bool allow_uninitialized_memory);
// AllocWorkbuf allocates the work buffer. The allocated buffer's length
// should be at least len_range.min_incl, but larger allocations (up to
// len_range.max_incl) may have better performance (by using more memory).
// The default AllocWorkbuf implementation allocates len_range.max_incl bytes
// of either uninitialized or zeroed memory.
virtual AllocWorkbufResult //
AllocWorkbuf(wuffs_base__range_ii_u64 len_range,
bool allow_uninitialized_memory);
// Done is always the last Callback method called by DecodeImage, whether or
// not parsing the input encountered an error. Even when successful, trailing
// data may remain in input and buffer.
// The image_decoder is the one returned by SelectDecoder (if SelectDecoder
// was successful), or a no-op unique_ptr otherwise. Like any unique_ptr,
// ownership moves to the Done implementation.
// Do not keep a reference to buffer or after Done returns,
// as DecodeImage may then de-allocate the backing array.
// The default Done implementation is a no-op, other than running the
// image_decoder unique_ptr destructor.
virtual void //
Done(DecodeImageResult& result,
sync_io::Input& input,
IOBuffer& buffer,
wuffs_base__image_decoder::unique_ptr image_decoder);
extern const char DecodeImage_BufferIsTooShort[];
extern const char DecodeImage_MaxInclDimensionExceeded[];
extern const char DecodeImage_MaxInclMetadataLengthExceeded[];
extern const char DecodeImage_OutOfMemory[];
extern const char DecodeImage_UnexpectedEndOfFile[];
extern const char DecodeImage_UnsupportedImageFormat[];
extern const char DecodeImage_UnsupportedMetadata[];
extern const char DecodeImage_UnsupportedPixelBlend[];
extern const char DecodeImage_UnsupportedPixelConfiguration[];
extern const char DecodeImage_UnsupportedPixelFormat[];
// The FooArgBar types add structure to Foo's optional arguments. They wrap
// inner representations for several reasons:
// - It provides a home for the DefaultValue static method, for Foo callers
// that want to override some but not all optional arguments.
// - It provides the "Bar" name at Foo call sites, which can help self-
// document Foo calls with many arguemnts.
// - It provides some type safety against accidentally transposing or omitting
// adjacent fundamentally-numeric-typed optional arguments.
// DecodeImageArgQuirks wraps an optional argument to DecodeImage.
struct DecodeImageArgQuirks {
explicit DecodeImageArgQuirks(wuffs_base__slice_u32 repr0);
explicit DecodeImageArgQuirks(uint32_t* ptr, size_t len);
// DefaultValue returns an empty slice.
static DecodeImageArgQuirks DefaultValue();
wuffs_base__slice_u32 repr;
// DecodeImageArgFlags wraps an optional argument to DecodeImage.
struct DecodeImageArgFlags {
explicit DecodeImageArgFlags(uint64_t repr0);
// DefaultValue returns 0.
static DecodeImageArgFlags DefaultValue();
// TODO: support all of the REPORT_METADATA_ETC flags, not just CHRM, EXIF,
// Background Color.
static constexpr uint64_t REPORT_METADATA_BGCL = 0x0001;
// Primary Chromaticities and White Point.
static constexpr uint64_t REPORT_METADATA_CHRM = 0x0002;
// Exchangeable Image File Format.
static constexpr uint64_t REPORT_METADATA_EXIF = 0x0004;
// Gamma Correction.
static constexpr uint64_t REPORT_METADATA_GAMA = 0x0008;
// International Color Consortium Profile.
static constexpr uint64_t REPORT_METADATA_ICCP = 0x0010;
// Key-Value Pair.
// For PNG files, this includes iTXt, tEXt and zTXt chunks. In the
// HandleMetadata callback, the raw argument contains UTF-8 strings.
static constexpr uint64_t REPORT_METADATA_KVP = 0x0020;
// Modification Time.
static constexpr uint64_t REPORT_METADATA_MTIM = 0x0040;
// Offset (2-Dimensional).
static constexpr uint64_t REPORT_METADATA_OFS2 = 0x0080;
// Physical Dimensions.
static constexpr uint64_t REPORT_METADATA_PHYD = 0x0100;
// Standard Red Green Blue (Rendering Intent).
static constexpr uint64_t REPORT_METADATA_SRGB = 0x0200;
// Extensible Metadata Platform.
static constexpr uint64_t REPORT_METADATA_XMP = 0x0400;
uint64_t repr;
// DecodeImageArgPixelBlend wraps an optional argument to DecodeImage.
struct DecodeImageArgPixelBlend {
explicit DecodeImageArgPixelBlend(wuffs_base__pixel_blend repr0);
// DefaultValue returns WUFFS_BASE__PIXEL_BLEND__SRC.
static DecodeImageArgPixelBlend DefaultValue();
wuffs_base__pixel_blend repr;
// DecodeImageArgBackgroundColor wraps an optional argument to DecodeImage.
struct DecodeImageArgBackgroundColor {
explicit DecodeImageArgBackgroundColor(
wuffs_base__color_u32_argb_premul repr0);
// DefaultValue returns 1, an invalid wuffs_base__color_u32_argb_premul.
static DecodeImageArgBackgroundColor DefaultValue();
wuffs_base__color_u32_argb_premul repr;
// DecodeImageArgMaxInclDimension wraps an optional argument to DecodeImage.
struct DecodeImageArgMaxInclDimension {
explicit DecodeImageArgMaxInclDimension(uint32_t repr0);
// DefaultValue returns 1048575 = 0x000F_FFFF, more than 1 million pixels.
static DecodeImageArgMaxInclDimension DefaultValue();
uint32_t repr;
// DecodeImageArgMaxInclMetadataLength wraps an optional argument to
// DecodeImage.
struct DecodeImageArgMaxInclMetadataLength {
explicit DecodeImageArgMaxInclMetadataLength(uint64_t repr0);
// DefaultValue returns 16777215 = 0x00FF_FFFF, one less than 16 MiB.
static DecodeImageArgMaxInclMetadataLength DefaultValue();
uint64_t repr;
// DecodeImage decodes the image data in input. A variety of image file formats
// can be decoded, depending on what callbacks.SelectDecoder returns.
// For animated formats, only the first frame is returned, since the API is
// simpler for synchronous I/O and having DecodeImage only return when
// completely done, but rendering animation often involves handling other
// events in between animation frames. To decode multiple frames of animated
// images, or for asynchronous I/O (e.g. when decoding an image streamed over
// the network), use Wuffs' lower level C API instead of its higher level,
// simplified C++ API (the wuffs_aux API).
// The DecodeImageResult's fields depend on whether decoding succeeded:
// - On total success, the error_message is empty and pixbuf.pixcfg.is_valid()
// is true.
// - On partial success (e.g. the input file was truncated but we are still
// able to decode some of the pixels), error_message is non-empty but
// pixbuf.pixcfg.is_valid() is still true. It is up to the caller whether to
// accept or reject partial success.
// - On failure, the error_message is non_empty and pixbuf.pixcfg.is_valid()
// is false.
// The callbacks allocate the pixel buffer memory and work buffer memory. On
// success, pixel buffer memory ownership is passed to the DecodeImage caller
// as the returned pixbuf_mem_owner. Regardless of success or failure, the work
// buffer memory is deleted.
// The pixel_blend (one of the constants listed below) determines how to
// composite the decoded image over the pixel buffer's original pixels (as
// returned by callbacks.AllocPixbuf):
// The background_color is used to fill the pixel buffer after
// callbacks.AllocPixbuf returns, if it is valid in the
// wuffs_base__color_u32_argb_premul__is_valid sense. The default value,
// 0x0000_0001, is not valid since its Blue channel value (0x01) is greater
// than its Alpha channel value (0x00). A valid background_color will typically
// be overwritten when pixel_blend is WUFFS_BASE__PIXEL_BLEND__SRC, but might
// still be visible on partial (not total) success or when pixel_blend is
// WUFFS_BASE__PIXEL_BLEND__SRC_OVER and the decoded image is not fully opaque.
// Decoding fails (with DecodeImage_MaxInclDimensionExceeded) if the image's
// width or height is greater than max_incl_dimension or if any opted-in (via
// flags bits) metadata is longer than max_incl_metadata_length.
DecodeImageResult //
DecodeImage(DecodeImageCallbacks& callbacks,
sync_io::Input& input,
DecodeImageArgQuirks quirks = DecodeImageArgQuirks::DefaultValue(),
DecodeImageArgFlags flags = DecodeImageArgFlags::DefaultValue(),
DecodeImageArgPixelBlend pixel_blend =
DecodeImageArgBackgroundColor background_color =
DecodeImageArgMaxInclDimension max_incl_dimension =
DecodeImageArgMaxInclMetadataLength max_incl_metadata_length =
} // namespace wuffs_aux