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Add Alpha Decode support from WebPDecode.

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Extend WebP decode functionality to extract Alpha data (support ALPH
chunk) and decode the Alpha plane using Alpha (utils/alpha) core-lib.

Change-Id: I6f0ee1b189c13caba3c1dd9b681383bfd00aa212
This commit is contained in:
Vikas Arora
2011-12-01 08:57:36 +05:30
parent e1947a9299
commit d117a94046
8 changed files with 62 additions and 77 deletions
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52
src/dec/alpha.c
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@ -10,11 +10,8 @@
// Author: Skal (pascal.massimino@gmail.com)
#include <stdlib.h>
#include "vp8i.h"
#ifdef WEBP_EXPERIMENTAL_FEATURES
#include "zlib.h"
#include "./vp8i.h"
#include "../utils/alpha.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
@ -24,46 +21,25 @@ extern "C" {
const uint8_t* VP8DecompressAlphaRows(VP8Decoder* const dec,
int row, int num_rows) {
uint8_t* output = dec->alpha_plane_;
const int stride = dec->pic_hdr_.width_;
if (row < 0 || row + num_rows > dec->pic_hdr_.height_) {
return NULL; // sanity check
if (row < 0 || num_rows < 0 || row + num_rows > dec->pic_hdr_.height_) {
return NULL; // sanity check.
}
if (row == 0) {
// TODO(skal): for now, we just decompress everything during the first call.
// Later, we'll decode progressively, but we need to store the
// z_stream state.
const uint8_t* data = dec->alpha_data_;
size_t data_size = dec->alpha_data_size_;
const size_t output_size = stride * dec->pic_hdr_.height_;
int ret = Z_OK;
z_stream strm;
memset(&strm, 0, sizeof(strm));
if (inflateInit(&strm) != Z_OK) {
return 0;
}
strm.avail_in = data_size;
strm.next_in = (unsigned char*)data;
do {
strm.avail_out = output_size;
strm.next_out = output;
ret = inflate(&strm, Z_NO_FLUSH);
if (ret == Z_NEED_DICT || ret == Z_DATA_ERROR || ret == Z_MEM_ERROR) {
break;
}
} while (strm.avail_out == 0);
inflateEnd(&strm);
if (ret != Z_STREAM_END) {
return NULL; // error
// 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 output + row * stride;
// Return a pointer to the current decoded row.
return dec->alpha_plane_ + row * stride;
}
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif
#endif // WEBP_EXPERIMENTAL_FEATURES