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decode.h (24342B)


      1 // Copyright 2010 Google Inc. All Rights Reserved.
      2 //
      3 // Use of this source code is governed by a BSD-style license
      4 // that can be found in the COPYING file in the root of the source
      5 // tree. An additional intellectual property rights grant can be found
      6 // in the file PATENTS. All contributing project authors may
      7 // be found in the AUTHORS file in the root of the source tree.
      8 // -----------------------------------------------------------------------------
      9 //
     10 //  Main decoding functions for WebP images.
     11 //
     12 // Author: Skal (pascal.massimino@gmail.com)
     13 
     14 #ifndef WEBP_WEBP_DECODE_H_
     15 #define WEBP_WEBP_DECODE_H_
     16 
     17 #include <stddef.h>
     18 
     19 #include "./types.h"
     20 
     21 #ifdef __cplusplus
     22 extern "C" {
     23 #endif
     24 
     25 #define WEBP_DECODER_ABI_VERSION 0x0210    // MAJOR(8b) + MINOR(8b)
     26 
     27 // Note: forward declaring enumerations is not allowed in (strict) C and C++,
     28 // the types are left here for reference.
     29 // typedef enum VP8StatusCode VP8StatusCode;
     30 // typedef enum WEBP_CSP_MODE WEBP_CSP_MODE;
     31 typedef struct WebPRGBABuffer WebPRGBABuffer;
     32 typedef struct WebPYUVABuffer WebPYUVABuffer;
     33 typedef struct WebPDecBuffer WebPDecBuffer;
     34 typedef struct WebPIDecoder WebPIDecoder;
     35 typedef struct WebPBitstreamFeatures WebPBitstreamFeatures;
     36 typedef struct WebPDecoderOptions WebPDecoderOptions;
     37 typedef struct WebPDecoderConfig WebPDecoderConfig;
     38 
     39 // Return the decoder's version number, packed in hexadecimal using 8bits for
     40 // each of major/minor/revision. E.g: v2.5.7 is 0x020507.
     41 WEBP_EXTERN int WebPGetDecoderVersion(void);
     42 
     43 // Retrieve basic header information: width, height.
     44 // This function will also validate the header, returning true on success,
     45 // false otherwise. '*width' and '*height' are only valid on successful return.
     46 // Pointers 'width' and 'height' can be passed NULL if deemed irrelevant.
     47 // Note: The following chunk sequences (before the raw VP8/VP8L data) are
     48 // considered valid by this function:
     49 // RIFF + VP8(L)
     50 // RIFF + VP8X + (optional chunks) + VP8(L)
     51 // ALPH + VP8 <-- Not a valid WebP format: only allowed for internal purpose.
     52 // VP8(L)     <-- Not a valid WebP format: only allowed for internal purpose.
     53 WEBP_NODISCARD WEBP_EXTERN int WebPGetInfo(
     54    const uint8_t* data, size_t data_size, int* width, int* height);
     55 
     56 // Decodes WebP images pointed to by 'data' and returns RGBA samples, along
     57 // with the dimensions in *width and *height. The ordering of samples in
     58 // memory is R, G, B, A, R, G, B, A... in scan order (endian-independent).
     59 // The returned pointer should be deleted calling WebPFree().
     60 // Returns NULL in case of error.
     61 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeRGBA(
     62    const uint8_t* data, size_t data_size, int* width, int* height);
     63 
     64 // Same as WebPDecodeRGBA, but returning A, R, G, B, A, R, G, B... ordered data.
     65 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeARGB(
     66    const uint8_t* data, size_t data_size, int* width, int* height);
     67 
     68 // Same as WebPDecodeRGBA, but returning B, G, R, A, B, G, R, A... ordered data.
     69 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeBGRA(
     70    const uint8_t* data, size_t data_size, int* width, int* height);
     71 
     72 // Same as WebPDecodeRGBA, but returning R, G, B, R, G, B... ordered data.
     73 // If the bitstream contains transparency, it is ignored.
     74 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeRGB(
     75    const uint8_t* data, size_t data_size, int* width, int* height);
     76 
     77 // Same as WebPDecodeRGB, but returning B, G, R, B, G, R... ordered data.
     78 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeBGR(
     79    const uint8_t* data, size_t data_size, int* width, int* height);
     80 
     81 // Decode WebP images pointed to by 'data' to Y'UV format(*). The pointer
     82 // returned is the Y samples buffer. Upon return, *u and *v will point to
     83 // the U and V chroma data. These U and V buffers need NOT be passed to
     84 // WebPFree(), unlike the returned Y luma one. The dimension of the U and V
     85 // planes are both (*width + 1) / 2 and (*height + 1) / 2.
     86 // Upon return, the Y buffer has a stride returned as '*stride', while U and V
     87 // have a common stride returned as '*uv_stride'.
     88 // 'width' and 'height' may be NULL, the other pointers must not be.
     89 // Returns NULL in case of error.
     90 // (*) Also named Y'CbCr. See: https://en.wikipedia.org/wiki/YCbCr
     91 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeYUV(
     92    const uint8_t* data, size_t data_size, int* width, int* height,
     93    uint8_t** u, uint8_t** v, int* stride, int* uv_stride);
     94 
     95 // These five functions are variants of the above ones, that decode the image
     96 // directly into a pre-allocated buffer 'output_buffer'. The maximum storage
     97 // available in this buffer is indicated by 'output_buffer_size'. If this
     98 // storage is not sufficient (or an error occurred), NULL is returned.
     99 // Otherwise, output_buffer is returned, for convenience.
    100 // The parameter 'output_stride' specifies the distance (in bytes)
    101 // between scanlines. Hence, output_buffer_size is expected to be at least
    102 // output_stride x picture-height.
    103 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeRGBAInto(
    104    const uint8_t* data, size_t data_size,
    105    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    106 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeARGBInto(
    107    const uint8_t* data, size_t data_size,
    108    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    109 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeBGRAInto(
    110    const uint8_t* data, size_t data_size,
    111    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    112 
    113 // RGB and BGR variants. Here too the transparency information, if present,
    114 // will be dropped and ignored.
    115 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeRGBInto(
    116    const uint8_t* data, size_t data_size,
    117    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    118 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeBGRInto(
    119    const uint8_t* data, size_t data_size,
    120    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    121 
    122 // WebPDecodeYUVInto() is a variant of WebPDecodeYUV() that operates directly
    123 // into pre-allocated luma/chroma plane buffers. This function requires the
    124 // strides to be passed: one for the luma plane and one for each of the
    125 // chroma ones. The size of each plane buffer is passed as 'luma_size',
    126 // 'u_size' and 'v_size' respectively.
    127 // Pointer to the luma plane ('*luma') is returned or NULL if an error occurred
    128 // during decoding (or because some buffers were found to be too small).
    129 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPDecodeYUVInto(
    130    const uint8_t* data, size_t data_size,
    131    uint8_t* luma, size_t luma_size, int luma_stride,
    132    uint8_t* u, size_t u_size, int u_stride,
    133    uint8_t* v, size_t v_size, int v_stride);
    134 
    135 //------------------------------------------------------------------------------
    136 // Output colorspaces and buffer
    137 
    138 // Colorspaces
    139 // Note: the naming describes the byte-ordering of packed samples in memory.
    140 // For instance, MODE_BGRA relates to samples ordered as B,G,R,A,B,G,R,A,...
    141 // Non-capital names (e.g.:MODE_Argb) relates to pre-multiplied RGB channels.
    142 // RGBA-4444 and RGB-565 colorspaces are represented by following byte-order:
    143 // RGBA-4444: [r3 r2 r1 r0 g3 g2 g1 g0], [b3 b2 b1 b0 a3 a2 a1 a0], ...
    144 // RGB-565: [r4 r3 r2 r1 r0 g5 g4 g3], [g2 g1 g0 b4 b3 b2 b1 b0], ...
    145 // In the case WEBP_SWAP_16BITS_CSP is defined, the bytes are swapped for
    146 // these two modes:
    147 // RGBA-4444: [b3 b2 b1 b0 a3 a2 a1 a0], [r3 r2 r1 r0 g3 g2 g1 g0], ...
    148 // RGB-565: [g2 g1 g0 b4 b3 b2 b1 b0], [r4 r3 r2 r1 r0 g5 g4 g3], ...
    149 
    150 typedef enum WEBP_CSP_MODE {
    151  MODE_RGB = 0, MODE_RGBA = 1,
    152  MODE_BGR = 2, MODE_BGRA = 3,
    153  MODE_ARGB = 4, MODE_RGBA_4444 = 5,
    154  MODE_RGB_565 = 6,
    155  // RGB-premultiplied transparent modes (alpha value is preserved)
    156  MODE_rgbA = 7,
    157  MODE_bgrA = 8,
    158  MODE_Argb = 9,
    159  MODE_rgbA_4444 = 10,
    160  // YUV modes must come after RGB ones.
    161  MODE_YUV = 11, MODE_YUVA = 12,  // yuv 4:2:0
    162  MODE_LAST = 13
    163 } WEBP_CSP_MODE;
    164 
    165 // Some useful macros:
    166 static WEBP_INLINE int WebPIsPremultipliedMode(WEBP_CSP_MODE mode) {
    167  return (mode == MODE_rgbA || mode == MODE_bgrA || mode == MODE_Argb ||
    168          mode == MODE_rgbA_4444);
    169 }
    170 
    171 static WEBP_INLINE int WebPIsAlphaMode(WEBP_CSP_MODE mode) {
    172  return (mode == MODE_RGBA || mode == MODE_BGRA || mode == MODE_ARGB ||
    173          mode == MODE_RGBA_4444 || mode == MODE_YUVA ||
    174          WebPIsPremultipliedMode(mode));
    175 }
    176 
    177 static WEBP_INLINE int WebPIsRGBMode(WEBP_CSP_MODE mode) {
    178  return (mode < MODE_YUV);
    179 }
    180 
    181 //------------------------------------------------------------------------------
    182 // WebPDecBuffer: Generic structure for describing the output sample buffer.
    183 
    184 struct WebPRGBABuffer {    // view as RGBA
    185  uint8_t* rgba;    // pointer to RGBA samples
    186  int stride;       // stride in bytes from one scanline to the next.
    187  size_t size;      // total size of the *rgba buffer.
    188 };
    189 
    190 struct WebPYUVABuffer {              // view as YUVA
    191  uint8_t* y, *u, *v, *a;     // pointer to luma, chroma U/V, alpha samples
    192  int y_stride;               // luma stride
    193  int u_stride, v_stride;     // chroma strides
    194  int a_stride;               // alpha stride
    195  size_t y_size;              // luma plane size
    196  size_t u_size, v_size;      // chroma planes size
    197  size_t a_size;              // alpha-plane size
    198 };
    199 
    200 // Output buffer
    201 struct WebPDecBuffer {
    202  WEBP_CSP_MODE colorspace;  // Colorspace.
    203  int width, height;         // Dimensions.
    204  int is_external_memory;    // If non-zero, 'internal_memory' pointer is not
    205                             // used. If value is '2' or more, the external
    206                             // memory is considered 'slow' and multiple
    207                             // read/write will be avoided.
    208  union {
    209    WebPRGBABuffer RGBA;
    210    WebPYUVABuffer YUVA;
    211  } u;                       // Nameless union of buffer parameters.
    212  uint32_t       pad[4];     // padding for later use
    213 
    214  uint8_t* private_memory;   // Internally allocated memory (only when
    215                             // is_external_memory is 0). Should not be used
    216                             // externally, but accessed via the buffer union.
    217 };
    218 
    219 // Internal, version-checked, entry point
    220 WEBP_NODISCARD WEBP_EXTERN int WebPInitDecBufferInternal(WebPDecBuffer*, int);
    221 
    222 // Initialize the structure as empty. Must be called before any other use.
    223 // Returns false in case of version mismatch
    224 WEBP_NODISCARD static WEBP_INLINE int WebPInitDecBuffer(WebPDecBuffer* buffer) {
    225  return WebPInitDecBufferInternal(buffer, WEBP_DECODER_ABI_VERSION);
    226 }
    227 
    228 // Free any memory associated with the buffer. Must always be called last.
    229 // Note: doesn't free the 'buffer' structure itself.
    230 WEBP_EXTERN void WebPFreeDecBuffer(WebPDecBuffer* buffer);
    231 
    232 //------------------------------------------------------------------------------
    233 // Enumeration of the status codes
    234 
    235 typedef enum WEBP_NODISCARD VP8StatusCode {
    236  VP8_STATUS_OK = 0,
    237  VP8_STATUS_OUT_OF_MEMORY,
    238  VP8_STATUS_INVALID_PARAM,
    239  VP8_STATUS_BITSTREAM_ERROR,
    240  VP8_STATUS_UNSUPPORTED_FEATURE,
    241  VP8_STATUS_SUSPENDED,
    242  VP8_STATUS_USER_ABORT,
    243  VP8_STATUS_NOT_ENOUGH_DATA
    244 } VP8StatusCode;
    245 
    246 //------------------------------------------------------------------------------
    247 // Incremental decoding
    248 //
    249 // This API allows streamlined decoding of partial data.
    250 // Picture can be incrementally decoded as data become available thanks to the
    251 // WebPIDecoder object. This object can be left in a SUSPENDED state if the
    252 // picture is only partially decoded, pending additional input.
    253 // Code example:
    254 /*
    255     WebPInitDecBuffer(&output_buffer);
    256     output_buffer.colorspace = mode;
    257     ...
    258     WebPIDecoder* idec = WebPINewDecoder(&output_buffer);
    259     while (additional_data_is_available) {
    260       // ... (get additional data in some new_data[] buffer)
    261       status = WebPIAppend(idec, new_data, new_data_size);
    262       if (status != VP8_STATUS_OK && status != VP8_STATUS_SUSPENDED) {
    263         break;    // an error occurred.
    264       }
    265 
    266       // The above call decodes the current available buffer.
    267       // Part of the image can now be refreshed by calling
    268       // WebPIDecGetRGB()/WebPIDecGetYUVA() etc.
    269     }
    270     WebPIDelete(idec);
    271 */
    272 
    273 // Creates a new incremental decoder with the supplied buffer parameter.
    274 // This output_buffer can be passed NULL, in which case a default output buffer
    275 // is used (with MODE_RGB). Otherwise, an internal reference to 'output_buffer'
    276 // is kept, which means that the lifespan of 'output_buffer' must be larger than
    277 // that of the returned WebPIDecoder object.
    278 // The supplied 'output_buffer' content MUST NOT be changed between calls to
    279 // WebPIAppend() or WebPIUpdate() unless 'output_buffer.is_external_memory' is
    280 // not set to 0. In such a case, it is allowed to modify the pointers, size and
    281 // stride of output_buffer.u.RGBA or output_buffer.u.YUVA, provided they remain
    282 // within valid bounds.
    283 // All other fields of WebPDecBuffer MUST remain constant between calls.
    284 // Returns NULL if the allocation failed.
    285 WEBP_NODISCARD WEBP_EXTERN WebPIDecoder* WebPINewDecoder(
    286    WebPDecBuffer* output_buffer);
    287 
    288 // This function allocates and initializes an incremental-decoder object, which
    289 // will output the RGB/A samples specified by 'csp' into a preallocated
    290 // buffer 'output_buffer'. The size of this buffer is at least
    291 // 'output_buffer_size' and the stride (distance in bytes between two scanlines)
    292 // is specified by 'output_stride'.
    293 // Additionally, output_buffer can be passed NULL in which case the output
    294 // buffer will be allocated automatically when the decoding starts. The
    295 // colorspace 'csp' is taken into account for allocating this buffer. All other
    296 // parameters are ignored.
    297 // Returns NULL if the allocation failed, or if some parameters are invalid.
    298 WEBP_NODISCARD WEBP_EXTERN WebPIDecoder* WebPINewRGB(
    299    WEBP_CSP_MODE csp,
    300    uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
    301 
    302 // This function allocates and initializes an incremental-decoder object, which
    303 // will output the raw luma/chroma samples into a preallocated planes if
    304 // supplied. The luma plane is specified by its pointer 'luma', its size
    305 // 'luma_size' and its stride 'luma_stride'. Similarly, the chroma-u plane
    306 // is specified by the 'u', 'u_size' and 'u_stride' parameters, and the chroma-v
    307 // plane by 'v' and 'v_size'. And same for the alpha-plane. The 'a' pointer
    308 // can be pass NULL in case one is not interested in the transparency plane.
    309 // Conversely, 'luma' can be passed NULL if no preallocated planes are supplied.
    310 // In this case, the output buffer will be automatically allocated (using
    311 // MODE_YUVA) when decoding starts. All parameters are then ignored.
    312 // Returns NULL if the allocation failed or if a parameter is invalid.
    313 WEBP_NODISCARD WEBP_EXTERN WebPIDecoder* WebPINewYUVA(
    314    uint8_t* luma, size_t luma_size, int luma_stride,
    315    uint8_t* u, size_t u_size, int u_stride,
    316    uint8_t* v, size_t v_size, int v_stride,
    317    uint8_t* a, size_t a_size, int a_stride);
    318 
    319 // Deprecated version of the above, without the alpha plane.
    320 // Kept for backward compatibility.
    321 WEBP_NODISCARD WEBP_EXTERN WebPIDecoder* WebPINewYUV(
    322    uint8_t* luma, size_t luma_size, int luma_stride,
    323    uint8_t* u, size_t u_size, int u_stride,
    324    uint8_t* v, size_t v_size, int v_stride);
    325 
    326 // Deletes the WebPIDecoder object and associated memory. Must always be called
    327 // if WebPINewDecoder, WebPINewRGB or WebPINewYUV succeeded.
    328 WEBP_EXTERN void WebPIDelete(WebPIDecoder* idec);
    329 
    330 // Copies and decodes the next available data. Returns VP8_STATUS_OK when
    331 // the image is successfully decoded. Returns VP8_STATUS_SUSPENDED when more
    332 // data is expected. Returns error in other cases.
    333 WEBP_EXTERN VP8StatusCode WebPIAppend(
    334    WebPIDecoder* idec, const uint8_t* data, size_t data_size);
    335 
    336 // A variant of the above function to be used when data buffer contains
    337 // partial data from the beginning. In this case data buffer is not copied
    338 // to the internal memory.
    339 // Note that the value of the 'data' pointer can change between calls to
    340 // WebPIUpdate, for instance when the data buffer is resized to fit larger data.
    341 WEBP_EXTERN VP8StatusCode WebPIUpdate(
    342    WebPIDecoder* idec, const uint8_t* data, size_t data_size);
    343 
    344 // Returns the RGB/A image decoded so far. Returns NULL if output params
    345 // are not initialized yet. The RGB/A output type corresponds to the colorspace
    346 // specified during call to WebPINewDecoder() or WebPINewRGB().
    347 // *last_y is the index of last decoded row in raster scan order. Some pointers
    348 // (*last_y, *width etc.) can be NULL if corresponding information is not
    349 // needed. The values in these pointers are only valid on successful (non-NULL)
    350 // return.
    351 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPIDecGetRGB(
    352    const WebPIDecoder* idec, int* last_y,
    353    int* width, int* height, int* stride);
    354 
    355 // Same as above function to get a YUVA image. Returns pointer to the luma
    356 // plane or NULL in case of error. If there is no alpha information
    357 // the alpha pointer '*a' will be returned NULL.
    358 WEBP_NODISCARD WEBP_EXTERN uint8_t* WebPIDecGetYUVA(
    359    const WebPIDecoder* idec, int* last_y,
    360    uint8_t** u, uint8_t** v, uint8_t** a,
    361    int* width, int* height, int* stride, int* uv_stride, int* a_stride);
    362 
    363 // Deprecated alpha-less version of WebPIDecGetYUVA(): it will ignore the
    364 // alpha information (if present). Kept for backward compatibility.
    365 WEBP_NODISCARD static WEBP_INLINE uint8_t* WebPIDecGetYUV(
    366    const WebPIDecoder* idec, int* last_y, uint8_t** u, uint8_t** v,
    367    int* width, int* height, int* stride, int* uv_stride) {
    368  return WebPIDecGetYUVA(idec, last_y, u, v, NULL, width, height,
    369                         stride, uv_stride, NULL);
    370 }
    371 
    372 // Generic call to retrieve information about the displayable area.
    373 // If non NULL, the left/right/width/height pointers are filled with the visible
    374 // rectangular area so far.
    375 // Returns NULL in case the incremental decoder object is in an invalid state.
    376 // Otherwise returns the pointer to the internal representation. This structure
    377 // is read-only, tied to WebPIDecoder's lifespan and should not be modified.
    378 WEBP_NODISCARD WEBP_EXTERN const WebPDecBuffer* WebPIDecodedArea(
    379    const WebPIDecoder* idec, int* left, int* top, int* width, int* height);
    380 
    381 //------------------------------------------------------------------------------
    382 // Advanced decoding parametrization
    383 //
    384 //  Code sample for using the advanced decoding API
    385 /*
    386     // A) Init a configuration object
    387     WebPDecoderConfig config;
    388     CHECK(WebPInitDecoderConfig(&config));
    389 
    390     // B) optional: retrieve the bitstream's features.
    391     CHECK(WebPGetFeatures(data, data_size, &config.input) == VP8_STATUS_OK);
    392 
    393     // C) Adjust 'config', if needed
    394     config.options.no_fancy_upsampling = 1;
    395     config.output.colorspace = MODE_BGRA;
    396     // etc.
    397 
    398     // Note that you can also make config.output point to an externally
    399     // supplied memory buffer, provided it's big enough to store the decoded
    400     // picture. Otherwise, config.output will just be used to allocate memory
    401     // and store the decoded picture.
    402 
    403     // D) Decode!
    404     CHECK(WebPDecode(data, data_size, &config) == VP8_STATUS_OK);
    405 
    406     // E) Decoded image is now in config.output (and config.output.u.RGBA)
    407 
    408     // F) Reclaim memory allocated in config's object. It's safe to call
    409     // this function even if the memory is external and wasn't allocated
    410     // by WebPDecode().
    411     WebPFreeDecBuffer(&config.output);
    412 */
    413 
    414 // Features gathered from the bitstream
    415 struct WebPBitstreamFeatures {
    416  int width;          // Width in pixels, as read from the bitstream.
    417  int height;         // Height in pixels, as read from the bitstream.
    418  int has_alpha;      // True if the bitstream contains an alpha channel.
    419  int has_animation;  // True if the bitstream is an animation.
    420  int format;         // 0 = undefined (/mixed), 1 = lossy, 2 = lossless
    421 
    422  uint32_t pad[5];    // padding for later use
    423 };
    424 
    425 // Internal, version-checked, entry point
    426 WEBP_EXTERN VP8StatusCode WebPGetFeaturesInternal(
    427    const uint8_t*, size_t, WebPBitstreamFeatures*, int);
    428 
    429 // Retrieve features from the bitstream. The *features structure is filled
    430 // with information gathered from the bitstream.
    431 // Returns VP8_STATUS_OK when the features are successfully retrieved. Returns
    432 // VP8_STATUS_NOT_ENOUGH_DATA when more data is needed to retrieve the
    433 // features from headers. Returns error in other cases.
    434 // Note: The following chunk sequences (before the raw VP8/VP8L data) are
    435 // considered valid by this function:
    436 // RIFF + VP8(L)
    437 // RIFF + VP8X + (optional chunks) + VP8(L)
    438 // ALPH + VP8 <-- Not a valid WebP format: only allowed for internal purpose.
    439 // VP8(L)     <-- Not a valid WebP format: only allowed for internal purpose.
    440 static WEBP_INLINE VP8StatusCode WebPGetFeatures(
    441    const uint8_t* data, size_t data_size,
    442    WebPBitstreamFeatures* features) {
    443  return WebPGetFeaturesInternal(data, data_size, features,
    444                                 WEBP_DECODER_ABI_VERSION);
    445 }
    446 
    447 // Decoding options
    448 struct WebPDecoderOptions {
    449  int bypass_filtering;               // if true, skip the in-loop filtering
    450  int no_fancy_upsampling;            // if true, use faster pointwise upsampler
    451  int use_cropping;                   // if true, cropping is applied _first_
    452  int crop_left, crop_top;            // top-left position for cropping.
    453                                      // Will be snapped to even values.
    454  int crop_width, crop_height;        // dimension of the cropping area
    455  int use_scaling;                    // if true, scaling is applied _afterward_
    456  int scaled_width, scaled_height;    // final resolution. if one is 0, it is
    457                                      // guessed from the other one to keep the
    458                                      // original ratio.
    459  int use_threads;                    // if true, use multi-threaded decoding
    460  int dithering_strength;             // dithering strength (0=Off, 100=full)
    461  int flip;                           // if true, flip output vertically
    462  int alpha_dithering_strength;       // alpha dithering strength in [0..100]
    463 
    464  uint32_t pad[5];                    // padding for later use
    465 };
    466 
    467 // Main object storing the configuration for advanced decoding.
    468 struct WebPDecoderConfig {
    469  WebPBitstreamFeatures input;  // Immutable bitstream features (optional)
    470  WebPDecBuffer output;         // Output buffer (can point to external mem)
    471  WebPDecoderOptions options;   // Decoding options
    472 };
    473 
    474 // Internal, version-checked, entry point
    475 WEBP_NODISCARD WEBP_EXTERN int WebPInitDecoderConfigInternal(WebPDecoderConfig*,
    476                                                             int);
    477 
    478 // Initialize the configuration as empty. This function must always be
    479 // called first, unless WebPGetFeatures() is to be called.
    480 // Returns false in case of mismatched version.
    481 WEBP_NODISCARD static WEBP_INLINE int WebPInitDecoderConfig(
    482    WebPDecoderConfig* config) {
    483  return WebPInitDecoderConfigInternal(config, WEBP_DECODER_ABI_VERSION);
    484 }
    485 
    486 // Returns true if 'config' is non-NULL and all configuration parameters are
    487 // within their valid ranges.
    488 WEBP_NODISCARD WEBP_EXTERN int WebPValidateDecoderConfig(
    489    const WebPDecoderConfig* config);
    490 
    491 // Instantiate a new incremental decoder object with the requested
    492 // configuration. The bitstream can be passed using 'data' and 'data_size'
    493 // parameter, in which case the features will be parsed and stored into
    494 // config->input. Otherwise, 'data' can be NULL and no parsing will occur.
    495 // Note that 'config' can be NULL too, in which case a default configuration
    496 // is used. If 'config' is not NULL, it must outlive the WebPIDecoder object
    497 // as some references to its fields will be used. No internal copy of 'config'
    498 // is made.
    499 // The return WebPIDecoder object must always be deleted calling WebPIDelete().
    500 // Returns NULL in case of error (and config->status will then reflect
    501 // the error condition, if available).
    502 WEBP_NODISCARD WEBP_EXTERN WebPIDecoder* WebPIDecode(
    503    const uint8_t* data, size_t data_size, WebPDecoderConfig* config);
    504 
    505 // Non-incremental version. This version decodes the full data at once, taking
    506 // 'config' into account. Returns decoding status (which should be VP8_STATUS_OK
    507 // if the decoding was successful). Note that 'config' cannot be NULL.
    508 WEBP_EXTERN VP8StatusCode WebPDecode(const uint8_t* data, size_t data_size,
    509                                     WebPDecoderConfig* config);
    510 
    511 #ifdef __cplusplus
    512 }    // extern "C"
    513 #endif
    514 
    515 #endif  // WEBP_WEBP_DECODE_H_