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// Copyright 2010 Google Inc. All Rights Reserved.
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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// Main decoding functions for WebP images.
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// Author: Skal (pascal.massimino@gmail.com)
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#ifndef WEBP_WEBP_DECODE_H_
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#define WEBP_WEBP_DECODE_H_
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#define WEBP_DECODER_ABI_VERSION 0x0203 // MAJOR(8b) + MINOR(8b)
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// Note: forward declaring enumerations is not allowed in (strict) C and C++,
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// the types are left here for reference.
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// typedef enum VP8StatusCode VP8StatusCode;
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// typedef enum WEBP_CSP_MODE WEBP_CSP_MODE;
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typedef struct WebPRGBABuffer WebPRGBABuffer;
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typedef struct WebPYUVABuffer WebPYUVABuffer;
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typedef struct WebPDecBuffer WebPDecBuffer;
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typedef struct WebPIDecoder WebPIDecoder;
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typedef struct WebPBitstreamFeatures WebPBitstreamFeatures;
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typedef struct WebPDecoderOptions WebPDecoderOptions;
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typedef struct WebPDecoderConfig WebPDecoderConfig;
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// Return the decoder's version number, packed in hexadecimal using 8bits for
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// each of major/minor/revision. E.g: v2.5.7 is 0x020507.
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WEBP_EXTERN(int) WebPGetDecoderVersion(void);
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// Retrieve basic header information: width, height.
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// This function will also validate the header and return 0 in
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// case of formatting error.
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// Pointers 'width' and 'height' can be passed NULL if deemed irrelevant.
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WEBP_EXTERN(int) WebPGetInfo(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Decodes WebP images pointed to by 'data' and returns RGBA samples, along
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// with the dimensions in *width and *height. The ordering of samples in
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// memory is R, G, B, A, R, G, B, A... in scan order (endian-independent).
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// The returned pointer should be deleted calling free().
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// Returns NULL in case of error.
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WEBP_EXTERN(uint8_t*) WebPDecodeRGBA(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Same as WebPDecodeRGBA, but returning A, R, G, B, A, R, G, B... ordered data.
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WEBP_EXTERN(uint8_t*) WebPDecodeARGB(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Same as WebPDecodeRGBA, but returning B, G, R, A, B, G, R, A... ordered data.
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WEBP_EXTERN(uint8_t*) WebPDecodeBGRA(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Same as WebPDecodeRGBA, but returning R, G, B, R, G, B... ordered data.
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// If the bitstream contains transparency, it is ignored.
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WEBP_EXTERN(uint8_t*) WebPDecodeRGB(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Same as WebPDecodeRGB, but returning B, G, R, B, G, R... ordered data.
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WEBP_EXTERN(uint8_t*) WebPDecodeBGR(const uint8_t* data, size_t data_size,
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int* width, int* height);
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// Decode WebP images pointed to by 'data' to Y'UV format(*). The pointer
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// returned is the Y samples buffer. Upon return, *u and *v will point to
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// the U and V chroma data. These U and V buffers need NOT be free()'d,
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// unlike the returned Y luma one. The dimension of the U and V planes
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// are both (*width + 1) / 2 and (*height + 1)/ 2.
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// Upon return, the Y buffer has a stride returned as '*stride', while U and V
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// have a common stride returned as '*uv_stride'.
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// Return NULL in case of error.
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// (*) Also named Y'CbCr. See: http://en.wikipedia.org/wiki/YCbCr
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WEBP_EXTERN(uint8_t*) WebPDecodeYUV(const uint8_t* data, size_t data_size,
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int* width, int* height,
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uint8_t** u, uint8_t** v,
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int* stride, int* uv_stride);
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// These five functions are variants of the above ones, that decode the image
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// directly into a pre-allocated buffer 'output_buffer'. The maximum storage
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// available in this buffer is indicated by 'output_buffer_size'. If this
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// storage is not sufficient (or an error occurred), NULL is returned.
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// Otherwise, output_buffer is returned, for convenience.
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// The parameter 'output_stride' specifies the distance (in bytes)
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// between scanlines. Hence, output_buffer_size is expected to be at least
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// output_stride x picture-height.
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WEBP_EXTERN(uint8_t*) WebPDecodeRGBAInto(
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const uint8_t* data, size_t data_size,
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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WEBP_EXTERN(uint8_t*) WebPDecodeARGBInto(
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const uint8_t* data, size_t data_size,
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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WEBP_EXTERN(uint8_t*) WebPDecodeBGRAInto(
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const uint8_t* data, size_t data_size,
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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// RGB and BGR variants. Here too the transparency information, if present,
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// will be dropped and ignored.
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WEBP_EXTERN(uint8_t*) WebPDecodeRGBInto(
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const uint8_t* data, size_t data_size,
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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WEBP_EXTERN(uint8_t*) WebPDecodeBGRInto(
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const uint8_t* data, size_t data_size,
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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// WebPDecodeYUVInto() is a variant of WebPDecodeYUV() that operates directly
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// into pre-allocated luma/chroma plane buffers. This function requires the
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// strides to be passed: one for the luma plane and one for each of the
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// chroma ones. The size of each plane buffer is passed as 'luma_size',
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// 'u_size' and 'v_size' respectively.
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// Pointer to the luma plane ('*luma') is returned or NULL if an error occurred
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// during decoding (or because some buffers were found to be too small).
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WEBP_EXTERN(uint8_t*) WebPDecodeYUVInto(
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const uint8_t* data, size_t data_size,
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uint8_t* luma, size_t luma_size, int luma_stride,
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uint8_t* u, size_t u_size, int u_stride,
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uint8_t* v, size_t v_size, int v_stride);
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//------------------------------------------------------------------------------
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// Output colorspaces and buffer
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// Note: the naming describes the byte-ordering of packed samples in memory.
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// For instance, MODE_BGRA relates to samples ordered as B,G,R,A,B,G,R,A,...
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// Non-capital names (e.g.:MODE_Argb) relates to pre-multiplied RGB channels.
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// RGBA-4444 and RGB-565 colorspaces are represented by following byte-order:
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// RGBA-4444: [r3 r2 r1 r0 g3 g2 g1 g0], [b3 b2 b1 b0 a3 a2 a1 a0], ...
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// RGB-565: [r4 r3 r2 r1 r0 g5 g4 g3], [g2 g1 g0 b4 b3 b2 b1 b0], ...
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// In the case WEBP_SWAP_16BITS_CSP is defined, the bytes are swapped for
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// RGBA-4444: [b3 b2 b1 b0 a3 a2 a1 a0], [r3 r2 r1 r0 g3 g2 g1 g0], ...
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// RGB-565: [g2 g1 g0 b4 b3 b2 b1 b0], [r4 r3 r2 r1 r0 g5 g4 g3], ...
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typedef enum WEBP_CSP_MODE {
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MODE_RGB = 0, MODE_RGBA = 1,
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MODE_BGR = 2, MODE_BGRA = 3,
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MODE_ARGB = 4, MODE_RGBA_4444 = 5,
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// RGB-premultiplied transparent modes (alpha value is preserved)
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// YUV modes must come after RGB ones.
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MODE_YUV = 11, MODE_YUVA = 12, // yuv 4:2:0
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// Some useful macros:
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static WEBP_INLINE int WebPIsPremultipliedMode(WEBP_CSP_MODE mode) {
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return (mode == MODE_rgbA || mode == MODE_bgrA || mode == MODE_Argb ||
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mode == MODE_rgbA_4444);
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static WEBP_INLINE int WebPIsAlphaMode(WEBP_CSP_MODE mode) {
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return (mode == MODE_RGBA || mode == MODE_BGRA || mode == MODE_ARGB ||
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mode == MODE_RGBA_4444 || mode == MODE_YUVA ||
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WebPIsPremultipliedMode(mode));
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static WEBP_INLINE int WebPIsRGBMode(WEBP_CSP_MODE mode) {
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return (mode < MODE_YUV);
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//------------------------------------------------------------------------------
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// WebPDecBuffer: Generic structure for describing the output sample buffer.
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struct WebPRGBABuffer { // view as RGBA
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uint8_t* rgba; // pointer to RGBA samples
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int stride; // stride in bytes from one scanline to the next.
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size_t size; // total size of the *rgba buffer.
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struct WebPYUVABuffer { // view as YUVA
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uint8_t* y, *u, *v, *a; // pointer to luma, chroma U/V, alpha samples
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int y_stride; // luma stride
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int u_stride, v_stride; // chroma strides
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int a_stride; // alpha stride
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size_t y_size; // luma plane size
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size_t u_size, v_size; // chroma planes size
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size_t a_size; // alpha-plane size
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struct WebPDecBuffer {
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WEBP_CSP_MODE colorspace; // Colorspace.
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int width, height; // Dimensions.
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int is_external_memory; // If true, 'internal_memory' pointer is not used.
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} u; // Nameless union of buffer parameters.
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uint32_t pad[4]; // padding for later use
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uint8_t* private_memory; // Internally allocated memory (only when
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// is_external_memory is false). Should not be used
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// externally, but accessed via the buffer union.
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// Internal, version-checked, entry point
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WEBP_EXTERN(int) WebPInitDecBufferInternal(WebPDecBuffer*, int);
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// Initialize the structure as empty. Must be called before any other use.
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// Returns false in case of version mismatch
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static WEBP_INLINE int WebPInitDecBuffer(WebPDecBuffer* buffer) {
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return WebPInitDecBufferInternal(buffer, WEBP_DECODER_ABI_VERSION);
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// Free any memory associated with the buffer. Must always be called last.
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// Note: doesn't free the 'buffer' structure itself.
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WEBP_EXTERN(void) WebPFreeDecBuffer(WebPDecBuffer* buffer);
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//------------------------------------------------------------------------------
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// Enumeration of the status codes
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typedef enum VP8StatusCode {
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VP8_STATUS_OUT_OF_MEMORY,
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VP8_STATUS_INVALID_PARAM,
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VP8_STATUS_BITSTREAM_ERROR,
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VP8_STATUS_UNSUPPORTED_FEATURE,
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VP8_STATUS_SUSPENDED,
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VP8_STATUS_USER_ABORT,
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VP8_STATUS_NOT_ENOUGH_DATA
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//------------------------------------------------------------------------------
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// Incremental decoding
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// This API allows streamlined decoding of partial data.
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// Picture can be incrementally decoded as data become available thanks to the
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// WebPIDecoder object. This object can be left in a SUSPENDED state if the
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// picture is only partially decoded, pending additional input.
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// WebPInitDecBuffer(&buffer);
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// buffer.colorspace = mode;
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// WebPIDecoder* idec = WebPINewDecoder(&buffer);
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// while (has_more_data) {
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// // ... (get additional data)
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// status = WebPIAppend(idec, new_data, new_data_size);
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// if (status != VP8_STATUS_SUSPENDED ||
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// // The above call decodes the current available buffer.
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// // Part of the image can now be refreshed by calling to
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// // WebPIDecGetRGB()/WebPIDecGetYUVA() etc.
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// WebPIDelete(idec);
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// Creates a new incremental decoder with the supplied buffer parameter.
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// This output_buffer can be passed NULL, in which case a default output buffer
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// is used (with MODE_RGB). Otherwise, an internal reference to 'output_buffer'
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// is kept, which means that the lifespan of 'output_buffer' must be larger than
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// that of the returned WebPIDecoder object.
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// The supplied 'output_buffer' content MUST NOT be changed between calls to
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// WebPIAppend() or WebPIUpdate() unless 'output_buffer.is_external_memory' is
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// set to 1. In such a case, it is allowed to modify the pointers, size and
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// stride of output_buffer.u.RGBA or output_buffer.u.YUVA, provided they remain
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// within valid bounds.
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// All other fields of WebPDecBuffer MUST remain constant between calls.
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// Returns NULL if the allocation failed.
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WEBP_EXTERN(WebPIDecoder*) WebPINewDecoder(WebPDecBuffer* output_buffer);
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// This function allocates and initializes an incremental-decoder object, which
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// will output the RGB/A samples specified by 'csp' into a preallocated
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// buffer 'output_buffer'. The size of this buffer is at least
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// 'output_buffer_size' and the stride (distance in bytes between two scanlines)
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// is specified by 'output_stride'.
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// Additionally, output_buffer can be passed NULL in which case the output
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// buffer will be allocated automatically when the decoding starts. The
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// colorspace 'csp' is taken into account for allocating this buffer. All other
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// parameters are ignored.
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// Returns NULL if the allocation failed, or if some parameters are invalid.
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WEBP_EXTERN(WebPIDecoder*) WebPINewRGB(
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uint8_t* output_buffer, size_t output_buffer_size, int output_stride);
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// This function allocates and initializes an incremental-decoder object, which
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// will output the raw luma/chroma samples into a preallocated planes if
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// supplied. The luma plane is specified by its pointer 'luma', its size
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// 'luma_size' and its stride 'luma_stride'. Similarly, the chroma-u plane
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// is specified by the 'u', 'u_size' and 'u_stride' parameters, and the chroma-v
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// plane by 'v' and 'v_size'. And same for the alpha-plane. The 'a' pointer
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// can be pass NULL in case one is not interested in the transparency plane.
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// Conversely, 'luma' can be passed NULL if no preallocated planes are supplied.
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// In this case, the output buffer will be automatically allocated (using
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// MODE_YUVA) when decoding starts. All parameters are then ignored.
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// Returns NULL if the allocation failed or if a parameter is invalid.
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WEBP_EXTERN(WebPIDecoder*) WebPINewYUVA(
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uint8_t* luma, size_t luma_size, int luma_stride,
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uint8_t* u, size_t u_size, int u_stride,
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uint8_t* v, size_t v_size, int v_stride,
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uint8_t* a, size_t a_size, int a_stride);
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// Deprecated version of the above, without the alpha plane.
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// Kept for backward compatibility.
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WEBP_EXTERN(WebPIDecoder*) WebPINewYUV(
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uint8_t* luma, size_t luma_size, int luma_stride,
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uint8_t* u, size_t u_size, int u_stride,
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uint8_t* v, size_t v_size, int v_stride);
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// Deletes the WebPIDecoder object and associated memory. Must always be called
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// if WebPINewDecoder, WebPINewRGB or WebPINewYUV succeeded.
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WEBP_EXTERN(void) WebPIDelete(WebPIDecoder* idec);
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// Copies and decodes the next available data. Returns VP8_STATUS_OK when
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// the image is successfully decoded. Returns VP8_STATUS_SUSPENDED when more
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// data is expected. Returns error in other cases.
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WEBP_EXTERN(VP8StatusCode) WebPIAppend(
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WebPIDecoder* idec, const uint8_t* data, size_t data_size);
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// A variant of the above function to be used when data buffer contains
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// partial data from the beginning. In this case data buffer is not copied
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// to the internal memory.
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// Note that the value of the 'data' pointer can change between calls to
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// WebPIUpdate, for instance when the data buffer is resized to fit larger data.
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WEBP_EXTERN(VP8StatusCode) WebPIUpdate(
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WebPIDecoder* idec, const uint8_t* data, size_t data_size);
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// Returns the RGB/A image decoded so far. Returns NULL if output params
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// are not initialized yet. The RGB/A output type corresponds to the colorspace
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// specified during call to WebPINewDecoder() or WebPINewRGB().
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// *last_y is the index of last decoded row in raster scan order. Some pointers
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// (*last_y, *width etc.) can be NULL if corresponding information is not
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WEBP_EXTERN(uint8_t*) WebPIDecGetRGB(
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const WebPIDecoder* idec, int* last_y,
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int* width, int* height, int* stride);
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// Same as above function to get a YUVA image. Returns pointer to the luma
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// plane or NULL in case of error. If there is no alpha information
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// the alpha pointer '*a' will be returned NULL.
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WEBP_EXTERN(uint8_t*) WebPIDecGetYUVA(
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const WebPIDecoder* idec, int* last_y,
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uint8_t** u, uint8_t** v, uint8_t** a,
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int* width, int* height, int* stride, int* uv_stride, int* a_stride);
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// Deprecated alpha-less version of WebPIDecGetYUVA(): it will ignore the
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// alpha information (if present). Kept for backward compatibility.
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static WEBP_INLINE uint8_t* WebPIDecGetYUV(
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const WebPIDecoder* idec, int* last_y, uint8_t** u, uint8_t** v,
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int* width, int* height, int* stride, int* uv_stride) {
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return WebPIDecGetYUVA(idec, last_y, u, v, NULL, width, height,
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stride, uv_stride, NULL);
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// Generic call to retrieve information about the displayable area.
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// If non NULL, the left/right/width/height pointers are filled with the visible
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// rectangular area so far.
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// Returns NULL in case the incremental decoder object is in an invalid state.
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// Otherwise returns the pointer to the internal representation. This structure
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// is read-only, tied to WebPIDecoder's lifespan and should not be modified.
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WEBP_EXTERN(const WebPDecBuffer*) WebPIDecodedArea(
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const WebPIDecoder* idec, int* left, int* top, int* width, int* height);
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//------------------------------------------------------------------------------
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// Advanced decoding parametrization
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// Code sample for using the advanced decoding API
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// A) Init a configuration object
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WebPDecoderConfig config;
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CHECK(WebPInitDecoderConfig(&config));
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// B) optional: retrieve the bitstream's features.
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CHECK(WebPGetFeatures(data, data_size, &config.input) == VP8_STATUS_OK);
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// C) Adjust 'config', if needed
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config.no_fancy_upsampling = 1;
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config.output.colorspace = MODE_BGRA;
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// Note that you can also make config.output point to an externally
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// supplied memory buffer, provided it's big enough to store the decoded
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// picture. Otherwise, config.output will just be used to allocate memory
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// and store the decoded picture.
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CHECK(WebPDecode(data, data_size, &config) == VP8_STATUS_OK);
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// E) Decoded image is now in config.output (and config.output.u.RGBA)
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// F) Reclaim memory allocated in config's object. It's safe to call
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// this function even if the memory is external and wasn't allocated
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WebPFreeDecBuffer(&config.output);
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// Features gathered from the bitstream
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struct WebPBitstreamFeatures {
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int width; // Width in pixels, as read from the bitstream.
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int height; // Height in pixels, as read from the bitstream.
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int has_alpha; // True if the bitstream contains an alpha channel.
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int has_animation; // True if the bitstream is an animation.
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int format; // 0 = undefined (/mixed), 1 = lossy, 2 = lossless
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int no_incremental_decoding; // if true, using incremental decoding is not
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int rotate; // TODO(later)
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int uv_sampling; // should be 0 for now. TODO(later)
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uint32_t pad[2]; // padding for later use
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// Internal, version-checked, entry point
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WEBP_EXTERN(VP8StatusCode) WebPGetFeaturesInternal(
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const uint8_t*, size_t, WebPBitstreamFeatures*, int);
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// Retrieve features from the bitstream. The *features structure is filled
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// with information gathered from the bitstream.
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// Returns VP8_STATUS_OK when the features are successfully retrieved. Returns
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// VP8_STATUS_NOT_ENOUGH_DATA when more data is needed to retrieve the
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// features from headers. Returns error in other cases.
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static WEBP_INLINE VP8StatusCode WebPGetFeatures(
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const uint8_t* data, size_t data_size,
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WebPBitstreamFeatures* features) {
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return WebPGetFeaturesInternal(data, data_size, features,
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WEBP_DECODER_ABI_VERSION);
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struct WebPDecoderOptions {
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int bypass_filtering; // if true, skip the in-loop filtering
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int no_fancy_upsampling; // if true, use faster pointwise upsampler
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int use_cropping; // if true, cropping is applied _first_
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int crop_left, crop_top; // top-left position for cropping.
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// Will be snapped to even values.
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int crop_width, crop_height; // dimension of the cropping area
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int use_scaling; // if true, scaling is applied _afterward_
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int scaled_width, scaled_height; // final resolution
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int use_threads; // if true, use multi-threaded decoding
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int dithering_strength; // dithering strength (0=Off, 100=full)
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#if WEBP_DECODER_ABI_VERSION > 0x0203
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int flip; // flip output vertically
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int alpha_dithering_strength; // alpha dithering strength in [0..100]
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int force_rotation; // forced rotation (to be applied _last_)
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int no_enhancement; // if true, discard enhancement layer
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#if WEBP_DECODER_ABI_VERSION > 0x0203
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uint32_t pad[3]; // padding for later use
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uint32_t pad[5]; // padding for later use
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// Main object storing the configuration for advanced decoding.
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struct WebPDecoderConfig {
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WebPBitstreamFeatures input; // Immutable bitstream features (optional)
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WebPDecBuffer output; // Output buffer (can point to external mem)
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WebPDecoderOptions options; // Decoding options
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// Internal, version-checked, entry point
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WEBP_EXTERN(int) WebPInitDecoderConfigInternal(WebPDecoderConfig*, int);
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// Initialize the configuration as empty. This function must always be
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// called first, unless WebPGetFeatures() is to be called.
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// Returns false in case of mismatched version.
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static WEBP_INLINE int WebPInitDecoderConfig(WebPDecoderConfig* config) {
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return WebPInitDecoderConfigInternal(config, WEBP_DECODER_ABI_VERSION);
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// Instantiate a new incremental decoder object with the requested
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// configuration. The bitstream can be passed using 'data' and 'data_size'
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// parameter, in which case the features will be parsed and stored into
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// config->input. Otherwise, 'data' can be NULL and no parsing will occur.
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// Note that 'config' can be NULL too, in which case a default configuration
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// The return WebPIDecoder object must always be deleted calling WebPIDelete().
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// Returns NULL in case of error (and config->status will then reflect
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// the error condition).
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WEBP_EXTERN(WebPIDecoder*) WebPIDecode(const uint8_t* data, size_t data_size,
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WebPDecoderConfig* config);
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// Non-incremental version. This version decodes the full data at once, taking
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// 'config' into account. Returns decoding status (which should be VP8_STATUS_OK
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// if the decoding was successful).
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WEBP_EXTERN(VP8StatusCode) WebPDecode(const uint8_t* data, size_t data_size,
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WebPDecoderConfig* config);
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#endif /* WEBP_WEBP_DECODE_H_ */