summaryrefslogtreecommitdiffstats
path: root/media/libwebp/src/dec/alpha_dec.c
diff options
context:
space:
mode:
Diffstat (limited to 'media/libwebp/src/dec/alpha_dec.c')
-rw-r--r--media/libwebp/src/dec/alpha_dec.c232
1 files changed, 232 insertions, 0 deletions
diff --git a/media/libwebp/src/dec/alpha_dec.c b/media/libwebp/src/dec/alpha_dec.c
new file mode 100644
index 0000000000..bce735bfc2
--- /dev/null
+++ b/media/libwebp/src/dec/alpha_dec.c
@@ -0,0 +1,232 @@
+// 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;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-01 10:54:56 +0000