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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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