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- // Copyright 2011 Google Inc. All Rights Reserved.
- //
- // Use of this source code is governed by a BSD-style license
- // that can be found in the COPYING file in the root of the source
- // tree. An additional intellectual property rights grant can be found
- // in the file PATENTS. All contributing project authors may
- // be found in the AUTHORS file in the root of the source tree.
- // -----------------------------------------------------------------------------
- //
- // Alpha-plane decompression.
- //
- // Author: Skal (pascal.massimino@gmail.com)
- #include <stdlib.h>
- #include "./alphai.h"
- #include "./vp8i.h"
- #include "./vp8li.h"
- #include "../utils/quant_levels_dec.h"
- #include "../utils/utils.h"
- #include "../webp/format_constants.h"
- //------------------------------------------------------------------------------
- // ALPHDecoder object.
- ALPHDecoder* ALPHNew(void) {
- ALPHDecoder* const dec = (ALPHDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
- return dec;
- }
- void ALPHDelete(ALPHDecoder* const dec) {
- if (dec != NULL) {
- VP8LDelete(dec->vp8l_dec_);
- dec->vp8l_dec_ = NULL;
- WebPSafeFree(dec);
- }
- }
- //------------------------------------------------------------------------------
- // Decoding.
- // Initialize alpha decoding by parsing the alpha header and decoding the image
- // header for alpha data stored using lossless compression.
- // Returns false in case of error in alpha header (data too short, invalid
- // compression method or filter, error in lossless header data etc).
- static int ALPHInit(ALPHDecoder* const dec, const uint8_t* data,
- size_t data_size, int width, int height, uint8_t* output) {
- int ok = 0;
- const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
- const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
- int rsrv;
- assert(width > 0 && height > 0);
- assert(data != NULL && output != NULL);
- dec->width_ = width;
- dec->height_ = height;
- if (data_size <= ALPHA_HEADER_LEN) {
- return 0;
- }
- dec->method_ = (data[0] >> 0) & 0x03;
- dec->filter_ = (data[0] >> 2) & 0x03;
- dec->pre_processing_ = (data[0] >> 4) & 0x03;
- rsrv = (data[0] >> 6) & 0x03;
- if (dec->method_ < ALPHA_NO_COMPRESSION ||
- dec->method_ > ALPHA_LOSSLESS_COMPRESSION ||
- dec->filter_ >= WEBP_FILTER_LAST ||
- dec->pre_processing_ > ALPHA_PREPROCESSED_LEVELS ||
- rsrv != 0) {
- return 0;
- }
- if (dec->method_ == ALPHA_NO_COMPRESSION) {
- const size_t alpha_decoded_size = dec->width_ * dec->height_;
- ok = (alpha_data_size >= alpha_decoded_size);
- } else {
- assert(dec->method_ == ALPHA_LOSSLESS_COMPRESSION);
- ok = VP8LDecodeAlphaHeader(dec, alpha_data, alpha_data_size, output);
- }
- return ok;
- }
- // Decodes, unfilters and dequantizes *at least* 'num_rows' rows of alpha
- // starting from row number 'row'. It assumes that rows up to (row - 1) have
- // already been decoded.
- // Returns false in case of bitstream error.
- static int ALPHDecode(VP8Decoder* const dec, int row, int num_rows) {
- ALPHDecoder* const alph_dec = dec->alph_dec_;
- const int width = alph_dec->width_;
- const int height = alph_dec->height_;
- WebPUnfilterFunc unfilter_func = WebPUnfilters[alph_dec->filter_];
- uint8_t* const output = dec->alpha_plane_;
- if (alph_dec->method_ == ALPHA_NO_COMPRESSION) {
- const size_t offset = row * width;
- const size_t num_pixels = num_rows * width;
- assert(dec->alpha_data_size_ >= ALPHA_HEADER_LEN + offset + num_pixels);
- memcpy(dec->alpha_plane_ + offset,
- dec->alpha_data_ + ALPHA_HEADER_LEN + offset, num_pixels);
- } else { // alph_dec->method_ == ALPHA_LOSSLESS_COMPRESSION
- assert(alph_dec->vp8l_dec_ != NULL);
- if (!VP8LDecodeAlphaImageStream(alph_dec, row + num_rows)) {
- return 0;
- }
- }
- if (unfilter_func != NULL) {
- unfilter_func(width, height, width, row, num_rows, output);
- }
- if (row + num_rows == dec->pic_hdr_.height_) {
- dec->is_alpha_decoded_ = 1;
- }
- return 1;
- }
- //------------------------------------------------------------------------------
- // Main entry point.
- const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
- int row, int num_rows) {
- const int width = dec->pic_hdr_.width_;
- const int height = dec->pic_hdr_.height_;
- if (row < 0 || num_rows <= 0 || row + num_rows > height) {
- return NULL; // sanity check.
- }
- if (row == 0) {
- // Initialize decoding.
- assert(dec->alpha_plane_ != NULL);
- dec->alph_dec_ = ALPHNew();
- if (dec->alph_dec_ == NULL) return NULL;
- if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
- width, height, dec->alpha_plane_)) {
- ALPHDelete(dec->alph_dec_);
- dec->alph_dec_ = NULL;
- return NULL;
- }
- // if we allowed use of alpha dithering, check whether it's needed at all
- if (dec->alph_dec_->pre_processing_ != ALPHA_PREPROCESSED_LEVELS) {
- dec->alpha_dithering_ = 0; // disable dithering
- } else {
- num_rows = height; // decode everything in one pass
- }
- }
- if (!dec->is_alpha_decoded_) {
- int ok = 0;
- assert(dec->alph_dec_ != NULL);
- ok = ALPHDecode(dec, row, num_rows);
- if (ok && dec->alpha_dithering_ > 0) {
- ok = WebPDequantizeLevels(dec->alpha_plane_, width, height,
- dec->alpha_dithering_);
- }
- if (!ok || dec->is_alpha_decoded_) {
- ALPHDelete(dec->alph_dec_);
- dec->alph_dec_ = NULL;
- }
- if (!ok) return NULL; // Error.
- }
- // Return a pointer to the current decoded row.
- return dec->alpha_plane_ + row * width;
- }
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