236 lines
8.0 KiB
C
236 lines
8.0 KiB
C
/**
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* =========================================================================
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* File : tex_codec.cpp
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* Project : 0 A.D.
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* Description : support routines and interface for texture codecs.
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* =========================================================================
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*/
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// license: GPL; see lib/license.txt
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#ifndef INCLUDED_TEX_CODEC
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#define INCLUDED_TEX_CODEC
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#include "tex.h"
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#include "tex_internal.h" // for codec's convenience
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#include "lib/allocators.h"
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/**
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* virtual method table for TexCodecs.
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* rationale: this works in C and also allows storing name and next in vtbl.
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* 'template method'-style interface to increase code reuse and
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* simplify writing new codecs.
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**/
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struct TexCodecVTbl
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{
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/**
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* decode the file into a Tex structure.
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*
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* @param da input data array (not const, because the texture
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* may have to be flipped in-place - see "texture orientation").
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* its size is guaranteed to be >= 4.
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* (usually enough to compare the header's "magic" field;
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* anyway, no legitimate file will be smaller)
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* @param t output texture object
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* @return LibError
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**/
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LibError (*decode)(DynArray * RESTRICT da, Tex * RESTRICT t);
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/**
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* encode the texture data into the codec's file format (in memory).
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*
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* @param t input texture object. note: non-const because encoding may
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* require a tex_transform.
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* @param da output data array, allocated by codec.
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* rationale: some codecs cannot calculate the output size beforehand
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* (e.g. PNG output via libpng), so the output memory cannot be allocated
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* by the caller.
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* @return LibError
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**/
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LibError (*encode)(Tex * RESTRICT t, DynArray * RESTRICT da);
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/**
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* transform the texture's pixel format.
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*
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* @param t texture object
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* @param transforms: OR-ed combination of TEX_* flags that are to
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* be changed. note: the codec needs only handle situations specific
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* to its format; generic pixel format transforms are handled by
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* the caller.
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**/
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LibError (*transform)(Tex* t, uint transforms);
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/**
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* indicate if the data appears to be an instance of this codec's header,
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* i.e. can this codec decode it?
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*
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* @param file input data; only guaranteed to be 4 bytes!
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* (this should be enough to examine the header's 'magic' field)
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* @return bool
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**/
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bool (*is_hdr)(const u8 * file);
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/**
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* is the extension that of a file format supported by this codec?
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*
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* rationale: cannot just return the extension string and have
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* caller compare it (-> smaller code) because a codec's file format
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* may have several valid extensions (e.g. jpg and jpeg).
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*
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* @param ext non-NULL extension string; does not contain '.'.
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* must be compared as case-insensitive.
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* @return bool
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**/
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bool (*is_ext)(const char* ext);
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/**
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* return size of the file header supported by this codec.
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*
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* @param file the specific header to return length of (taking its
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* variable-length fields into account). if NULL, return minimum
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* guaranteed header size, i.e. the header without any
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* variable-length fields.
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* @return size [bytes]
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**/
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size_t (*hdr_size)(const u8* file);
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/**
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* name of codec for debug purposes. typically set via TEX_CODEC_REGISTER.
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**/
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const char* name;
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/**
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* intrusive linked-list of codecs: more convenient than fixed-size
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* static storage.
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* set by caller; should be initialized to NULL.
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**/
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const TexCodecVTbl* next;
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};
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/**
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* build codec vtbl and register it. the codec will be queried for future
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* texture load requests. call order is undefined, but since each codec
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* only steps up if it can handle the given format, this is not a problem.
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*
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* @param name identifier of codec (not string!). used to bind 'member'
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* functions prefixed with it to the vtbl, and as the TexCodecVTbl name.
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* it should also mirror the default file extension (e.g. dds) -
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* this is relied upon (but verified) in the self-test.
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*
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* usage: at file scope within the source file containing the codec's methods.
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**/
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#define TEX_CODEC_REGISTER(name)\
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static TexCodecVTbl vtbl = \
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{\
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name##_decode, name##_encode, name##_transform,\
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name##_is_hdr, name##_is_ext, name##_hdr_size,\
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#name\
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};\
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/*static int dummy = tex_codec_register(&vtbl);*/\
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/* note: when building as a static library, pre-main initializers */\
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/* will not run! as a workaround, we build an externally visible */\
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/* registration function that must be called via */\
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/* tex_codec_register_all - see comments there. */\
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void name##_register() { tex_codec_register(&vtbl); }
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/**
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* add this vtbl to the codec list. called at NLSO init time by the
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* TEX_CODEC_REGISTER in each codec file.
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* order in list is unspecified; see TEX_CODEC_REGISTER.
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*
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* @param c pointer to vtbl.
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* @return int (allows calling from a macro at file scope; value is not used)
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**/
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extern int tex_codec_register(TexCodecVTbl* c);
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/**
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* find codec that recognizes the desired output file extension.
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*
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* @param fn filename; only the extension (that after '.') is used.
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* case-insensitive.
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* @param c (out) vtbl of responsible codec
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* @return LibError; ERR::RES_UNKNOWN_FORMAT (without warning, because this is
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* called by tex_is_known_extension) if no codec indicates they can
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* handle the given extension.
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**/
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extern LibError tex_codec_for_filename(const char* fn, const TexCodecVTbl** c);
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/**
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* find codec that recognizes the header's magic field.
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*
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* @param data typically contents of file, but need only include the
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* (first 4 bytes of) header.
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* @param data_size [bytes]
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* @param c (out) vtbl of responsible codec
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* @return LibError; ERR::RES_UNKNOWN_FORMAT if no codec indicates they can
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* handle the given format (header).
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**/
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extern LibError tex_codec_for_header(const u8* data, size_t data_size, const TexCodecVTbl** c);
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/**
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* enumerate all registered codecs.
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*
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* used by self-test to test each one of them in turn.
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*
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* @param prev_codec the last codec returned by this function.
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* pass 0 the first time.
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* note: this routine is stateless and therefore reentrant.
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* @return the next codec, or 0 if all have been returned.
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**/
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extern const TexCodecVTbl* tex_codec_next(const TexCodecVTbl* prev_codec);
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/**
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* transform the texture's pixel format.
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* tries each codec's transform method once, or until one indicates success.
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*
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* @param t texture object
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* @param transforms: OR-ed combination of TEX_* flags that are to
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* be changed.
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* @return LibError
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**/
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extern LibError tex_codec_transform(Tex* t, uint transforms);
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/**
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* allocate an array of row pointers that point into the given texture data.
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* for texture decoders that support output via row pointers (e.g. PNG),
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* this allows flipping the image vertically (useful when matching bottom-up
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* textures to a global orientation) directly, which is much more
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* efficient than transforming later via copying all pixels.
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*
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* @param data the texture data into which row pointers will point.
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* note: we don't allocate it here because this function is
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* needed for encoding, too (where data is already present).
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* @param h height [pixels] of texture.
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* @param pitch size [bytes] of one texture row, i.e. width*bytes_per_pixel.
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* @param src_flags TexFlags of source texture. used to extract its
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* orientation.
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* @param dst_orientation desired orientation of the output data.
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* can be one of TEX_BOTTOM_UP, TEX_TOP_DOWN, or 0 for the
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* "global orientation".
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* depending on src and dst, the row array is flipped if necessary.
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* @param rows (out) array of row pointers; caller must free() it when done.
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* @return LibError
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**/
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typedef const u8* RowPtr;
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typedef RowPtr* RowArray;
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extern LibError tex_codec_alloc_rows(const u8* data, size_t h, size_t pitch,
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uint src_flags, uint dst_orientation, RowArray& rows);
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/**
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* apply transforms and then copy header and image into output buffer.
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*
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* @param t input texture object
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* @param transforms transformations to be applied to pixel format
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* @param hdr header data
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* @param hdr_size [bytes]
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* @param da output data array (will be expanded as necessary)
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* @return LibError
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**/
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extern LibError tex_codec_write(Tex* t, uint transforms, const void* hdr, size_t hdr_size, DynArray* da);
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#endif // #ifndef INCLUDED_TEX_CODEC
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