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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 "src/dec/alphai_dec.h"
#include "src/dec/vp8i_dec.h"
#include "src/dec/vp8li_dec.h"
#include "src/dsp/dsp.h"
#include "src/utils/quant_levels_dec_utils.h"
#include "src/utils/utils.h"
#include "src/webp/format_constants.h"
//------------------------------------------------------------------------------
// ALPHDecoder object.
// Allocates a new alpha decoder instance.
static ALPHDecoder* ALPHNew(void) {
ALPHDecoder* const dec = (ALPHDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
return dec;
}
// Clears and deallocates an alpha decoder instance.
static 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, const VP8Io* const src_io,
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;
VP8Io* const io = &dec->io_;
assert(data != NULL && output != NULL && src_io != NULL);
VP8FiltersInit();
dec->output_ = output;
dec->width_ = src_io->width;
dec->height_ = src_io->height;
assert(dec->width_ > 0 && dec->height_ > 0);
if (data_size <= ALPHA_HEADER_LEN) {
return 0;
}
dec->method_ = (data[0] >> 0) & 0x03;
dec->filter_ = (WEBP_FILTER_TYPE)((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;
}
// Copy the necessary parameters from src_io to io
VP8InitIo(io);
WebPInitCustomIo(NULL, io);
io->opaque = dec;
io->width = src_io->width;
io->height = src_io->height;
io->use_cropping = src_io->use_cropping;
io->crop_left = src_io->crop_left;
io->crop_right = src_io->crop_right;
io->crop_top = src_io->crop_top;
io->crop_bottom = src_io->crop_bottom;
// No need to copy the scaling parameters.
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);
}
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->io_.crop_bottom;
if (alph_dec->method_ == ALPHA_NO_COMPRESSION) {
int y;
const uint8_t* prev_line = dec->alpha_prev_line_;
const uint8_t* deltas = dec->alpha_data_ + ALPHA_HEADER_LEN + row * width;
uint8_t* dst = dec->alpha_plane_ + row * width;
assert(deltas <= &dec->alpha_data_[dec->alpha_data_size_]);
if (alph_dec->filter_ != WEBP_FILTER_NONE) {
assert(WebPUnfilters[alph_dec->filter_] != NULL);
for (y = 0; y < num_rows; ++y) {
WebPUnfilters[alph_dec->filter_](prev_line, deltas, dst, width);
prev_line = dst;
dst += width;
deltas += width;
}
} else {
for (y = 0; y < num_rows; ++y) {
memcpy(dst, deltas, width * sizeof(*dst));
prev_line = dst;
dst += width;
deltas += width;
}
}
dec->alpha_prev_line_ = prev_line;
} else { // alph_dec->method_ == ALPHA_LOSSLESS_COMPRESSION
assert(alph_dec->vp8l_dec_ != NULL);
if (!VP8LDecodeAlphaImageStream(alph_dec, row + num_rows)) {
return 0;
}
}
if (row + num_rows >= height) {
dec->is_alpha_decoded_ = 1;
}
return 1;
}
static int AllocateAlphaPlane(VP8Decoder* const dec, const VP8Io* const io) {
const int stride = io->width;
const int height = io->crop_bottom;
const uint64_t alpha_size = (uint64_t)stride * height;
assert(dec->alpha_plane_mem_ == NULL);
dec->alpha_plane_mem_ =
(uint8_t*)WebPSafeMalloc(alpha_size, sizeof(*dec->alpha_plane_));
if (dec->alpha_plane_mem_ == NULL) {
return 0;
}
dec->alpha_plane_ = dec->alpha_plane_mem_;
dec->alpha_prev_line_ = NULL;
return 1;
}
void WebPDeallocateAlphaMemory(VP8Decoder* const dec) {
assert(dec != NULL);
WebPSafeFree(dec->alpha_plane_mem_);
dec->alpha_plane_mem_ = NULL;
dec->alpha_plane_ = NULL;
ALPHDelete(dec->alph_dec_);
dec->alph_dec_ = NULL;
}
//------------------------------------------------------------------------------
// Main entry point.
const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
const VP8Io* const io,
int row, int num_rows) {
const int width = io->width;
const int height = io->crop_bottom;
assert(dec != NULL && io != NULL);
if (row < 0 || num_rows <= 0 || row + num_rows > height) {
return NULL; // sanity check.
}
if (!dec->is_alpha_decoded_) {
if (dec->alph_dec_ == NULL) { // Initialize decoder.
dec->alph_dec_ = ALPHNew();
if (dec->alph_dec_ == NULL) return NULL;
if (!AllocateAlphaPlane(dec, io)) goto Error;
if (!ALPHInit(dec->alph_dec_, dec->alpha_data_, dec->alpha_data_size_,
io, dec->alpha_plane_)) {
goto Error;
}
// 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 - row; // decode everything in one pass
}
}
assert(dec->alph_dec_ != NULL);
assert(row + num_rows <= height);
if (!ALPHDecode(dec, row, num_rows)) goto Error;
if (dec->is_alpha_decoded_) { // finished?
ALPHDelete(dec->alph_dec_);
dec->alph_dec_ = NULL;
if (dec->alpha_dithering_ > 0) {
uint8_t* const alpha = dec->alpha_plane_ + io->crop_top * width
+ io->crop_left;
if (!WebPDequantizeLevels(alpha,
io->crop_right - io->crop_left,
io->crop_bottom - io->crop_top,
width, dec->alpha_dithering_)) {
goto Error;
}
}
}
}
// Return a pointer to the current decoded row.
return dec->alpha_plane_ + row * width;
Error:
WebPDeallocateAlphaMemory(dec);
return NULL;
}
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