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// Copyright 2011 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Alpha-plane decompression.
//
// Author: Skal (pascal.massimino@gmail.com)
#include <stdlib.h>
#include "./vp8i.h"
#include "./vp8li.h"
#include "../utils/filters.h"
#include "../utils/quant_levels_dec.h"
#include "../webp/format_constants.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
// TODO(skal): move to dsp/ ?
static void CopyPlane(const uint8_t* src, int src_stride,
uint8_t* dst, int dst_stride, int width, int height) {
while (height-- > 0) {
memcpy(dst, src, width);
src += src_stride;
dst += dst_stride;
}
}
//------------------------------------------------------------------------------
// Decodes the compressed data 'data' of size 'data_size' into the 'output'.
// The 'output' buffer should be pre-allocated and must be of the same
// dimension 'height'x'stride', as that of the image.
//
// Returns 1 on successfully decoding the compressed alpha and
// 0 if either:
// error in bit-stream header (invalid compression mode or filter), or
// error returned by appropriate compression method.
static int DecodeAlpha(const uint8_t* data, size_t data_size,
int width, int height, int stride, uint8_t* output) {
uint8_t* decoded_data = NULL;
const size_t decoded_size = height * width;
WEBP_FILTER_TYPE filter;
int pre_processing;
int rsrv;
int ok = 0;
int method;
assert(width > 0 && height > 0 && stride >= width);
assert(data != NULL && output != NULL);
if (data_size <= ALPHA_HEADER_LEN) {
return 0;
}
method = (data[0] >> 0) & 0x03;
filter = (data[0] >> 2) & 0x03;
pre_processing = (data[0] >> 4) & 0x03;
rsrv = (data[0] >> 6) & 0x03;
if (method < ALPHA_NO_COMPRESSION ||
method > ALPHA_LOSSLESS_COMPRESSION ||
filter >= WEBP_FILTER_LAST ||
pre_processing > ALPHA_PREPROCESSED_LEVELS ||
rsrv != 0) {
return 0;
}
if (method == ALPHA_NO_COMPRESSION) {
ok = (data_size >= decoded_size);
decoded_data = (uint8_t*)data + ALPHA_HEADER_LEN;
} else {
decoded_data = (uint8_t*)malloc(decoded_size);
if (decoded_data == NULL) return 0;
ok = VP8LDecodeAlphaImageStream(width, height,
data + ALPHA_HEADER_LEN,
data_size - ALPHA_HEADER_LEN,
decoded_data);
}
if (ok) {
WebPUnfilterFunc unfilter_func = WebPUnfilters[filter];
if (unfilter_func != NULL) {
// TODO(vikas): Implement on-the-fly decoding & filter mechanism to decode
// and apply filter per image-row.
unfilter_func(width, height, width, decoded_data);
}
// Construct raw_data (height x stride) from alpha data (height x width).
CopyPlane(decoded_data, width, output, stride, width, height);
if (pre_processing == ALPHA_PREPROCESSED_LEVELS) {
ok = DequantizeLevels(decoded_data, width, height);
}
}
if (method != ALPHA_NO_COMPRESSION) {
free(decoded_data);
}
return ok;
}
//------------------------------------------------------------------------------
const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
int row, int num_rows) {
const int stride = dec->pic_hdr_.width_;
if (row < 0 || num_rows < 0 || row + num_rows > dec->pic_hdr_.height_) {
return NULL; // sanity check.
}
if (row == 0) {
// Decode everything during the first call.
if (!DecodeAlpha(dec->alpha_data_, (size_t)dec->alpha_data_size_,
dec->pic_hdr_.width_, dec->pic_hdr_.height_, stride,
dec->alpha_plane_)) {
return NULL; // Error.
}
}
// Return a pointer to the current decoded row.
return dec->alpha_plane_ + row * stride;
}
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
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