116 lines
3.7 KiB
C
116 lines
3.7 KiB
C
// Copyright 2011 Google Inc. All Rights Reserved.
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//
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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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//
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// Alpha-plane decompression.
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//
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// Author: Skal (pascal.massimino@gmail.com)
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#include <stdlib.h>
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#include "./vp8i.h"
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#include "./vp8li.h"
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#include "../utils/filters.h"
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#include "../utils/quant_levels_dec.h"
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#include "../webp/format_constants.h"
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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//------------------------------------------------------------------------------
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// Decodes the compressed data 'data' of size 'data_size' into the 'output'.
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// The 'output' buffer should be pre-allocated and must be of the same
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// dimension 'height'x'width', as that of the image.
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//
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// Returns 1 on successfully decoding the compressed alpha and
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// 0 if either:
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// error in bit-stream header (invalid compression mode or filter), or
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// error returned by appropriate compression method.
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static int DecodeAlpha(const uint8_t* data, size_t data_size,
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int width, int height, uint8_t* output) {
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WEBP_FILTER_TYPE filter;
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int pre_processing;
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int rsrv;
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int ok = 0;
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int method;
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const uint8_t* const alpha_data = data + ALPHA_HEADER_LEN;
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const size_t alpha_data_size = data_size - ALPHA_HEADER_LEN;
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assert(width > 0 && height > 0);
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assert(data != NULL && output != NULL);
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if (data_size <= ALPHA_HEADER_LEN) {
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return 0;
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}
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method = (data[0] >> 0) & 0x03;
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filter = (data[0] >> 2) & 0x03;
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pre_processing = (data[0] >> 4) & 0x03;
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rsrv = (data[0] >> 6) & 0x03;
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if (method < ALPHA_NO_COMPRESSION ||
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method > ALPHA_LOSSLESS_COMPRESSION ||
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filter >= WEBP_FILTER_LAST ||
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pre_processing > ALPHA_PREPROCESSED_LEVELS ||
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rsrv != 0) {
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return 0;
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}
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if (method == ALPHA_NO_COMPRESSION) {
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const size_t alpha_decoded_size = height * width;
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ok = (alpha_data_size >= alpha_decoded_size);
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if (ok) memcpy(output, alpha_data, alpha_decoded_size);
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} else {
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ok = VP8LDecodeAlphaImageStream(width, height, alpha_data, alpha_data_size,
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output);
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}
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if (ok) {
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WebPUnfilterFunc unfilter_func = WebPUnfilters[filter];
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if (unfilter_func != NULL) {
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// TODO(vikas): Implement on-the-fly decoding & filter mechanism to decode
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// and apply filter per image-row.
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unfilter_func(width, height, width, output);
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}
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if (pre_processing == ALPHA_PREPROCESSED_LEVELS) {
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ok = DequantizeLevels(output, width, height);
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}
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}
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return ok;
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}
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//------------------------------------------------------------------------------
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const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
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int row, int num_rows) {
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const int width = dec->pic_hdr_.width_;
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const int height = dec->pic_hdr_.height_;
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if (row < 0 || num_rows < 0 || row + num_rows > height) {
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return NULL; // sanity check.
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}
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if (row == 0) {
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// Decode everything during the first call.
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assert(!dec->is_alpha_decoded_);
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if (!DecodeAlpha(dec->alpha_data_, (size_t)dec->alpha_data_size_,
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width, height, dec->alpha_plane_)) {
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return NULL; // Error.
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}
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dec->is_alpha_decoded_ = 1;
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}
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// Return a pointer to the current decoded row.
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return dec->alpha_plane_ + row * width;
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} // extern "C"
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#endif
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