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// Copyright 2015 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.
// -----------------------------------------------------------------------------
//
// AnimDecoder implementation.
//
#ifdef HAVE_CONFIG_H
#include "src/webp/config.h"
#endif
#include <assert.h>
#include <string.h>
#include "src/utils/utils.h"
#include "src/webp/decode.h"
#include "src/webp/demux.h"
#define NUM_CHANNELS 4
typedef void (*BlendRowFunc)(uint32_t* const, const uint32_t* const, int);
static void BlendPixelRowNonPremult(uint32_t* const src,
const uint32_t* const dst, int num_pixels);
static void BlendPixelRowPremult(uint32_t* const src, const uint32_t* const dst,
int num_pixels);
struct WebPAnimDecoder {
WebPDemuxer* demux_; // Demuxer created from given WebP bitstream.
WebPDecoderConfig config_; // Decoder config.
// Note: we use a pointer to a function blending multiple pixels at a time to
// allow possible inlining of per-pixel blending function.
BlendRowFunc blend_func_; // Pointer to the chose blend row function.
WebPAnimInfo info_; // Global info about the animation.
uint8_t* curr_frame_; // Current canvas (not disposed).
uint8_t* prev_frame_disposed_; // Previous canvas (properly disposed).
int prev_frame_timestamp_; // Previous frame timestamp (milliseconds).
WebPIterator prev_iter_; // Iterator object for previous frame.
int prev_frame_was_keyframe_; // True if previous frame was a keyframe.
int next_frame_; // Index of the next frame to be decoded
// (starting from 1).
};
static void DefaultDecoderOptions(WebPAnimDecoderOptions* const dec_options) {
dec_options->color_mode = MODE_RGBA;
dec_options->use_threads = 0;
}
int WebPAnimDecoderOptionsInitInternal(WebPAnimDecoderOptions* dec_options,
int abi_version) {
if (dec_options == NULL ||
WEBP_ABI_IS_INCOMPATIBLE(abi_version, WEBP_DEMUX_ABI_VERSION)) {
return 0;
}
DefaultDecoderOptions(dec_options);
return 1;
}
static int ApplyDecoderOptions(const WebPAnimDecoderOptions* const dec_options,
WebPAnimDecoder* const dec) {
WEBP_CSP_MODE mode;
WebPDecoderConfig* config = &dec->config_;
assert(dec_options != NULL);
mode = dec_options->color_mode;
if (mode != MODE_RGBA && mode != MODE_BGRA &&
mode != MODE_rgbA && mode != MODE_bgrA) {
return 0;
}
dec->blend_func_ = (mode == MODE_RGBA || mode == MODE_BGRA)
? &BlendPixelRowNonPremult
: &BlendPixelRowPremult;
WebPInitDecoderConfig(config);
config->output.colorspace = mode;
config->output.is_external_memory = 1;
config->options.use_threads = dec_options->use_threads;
// Note: config->output.u.RGBA is set at the time of decoding each frame.
return 1;
}
WebPAnimDecoder* WebPAnimDecoderNewInternal(
const WebPData* webp_data, const WebPAnimDecoderOptions* dec_options,
int abi_version) {
WebPAnimDecoderOptions options;
WebPAnimDecoder* dec = NULL;
WebPBitstreamFeatures features;
if (webp_data == NULL ||
WEBP_ABI_IS_INCOMPATIBLE(abi_version, WEBP_DEMUX_ABI_VERSION)) {
return NULL;
}
// Validate the bitstream before doing expensive allocations. The demuxer may
// be more tolerant than the decoder.
if (WebPGetFeatures(webp_data->bytes, webp_data->size, &features) !=
VP8_STATUS_OK) {
return NULL;
}
// Note: calloc() so that the pointer members are initialized to NULL.
dec = (WebPAnimDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
if (dec == NULL) goto Error;
if (dec_options != NULL) {
options = *dec_options;
} else {
DefaultDecoderOptions(&options);
}
if (!ApplyDecoderOptions(&options, dec)) goto Error;
dec->demux_ = WebPDemux(webp_data);
if (dec->demux_ == NULL) goto Error;
dec->info_.canvas_width = WebPDemuxGetI(dec->demux_, WEBP_FF_CANVAS_WIDTH);
dec->info_.canvas_height = WebPDemuxGetI(dec->demux_, WEBP_FF_CANVAS_HEIGHT);
dec->info_.loop_count = WebPDemuxGetI(dec->demux_, WEBP_FF_LOOP_COUNT);
dec->info_.bgcolor = WebPDemuxGetI(dec->demux_, WEBP_FF_BACKGROUND_COLOR);
dec->info_.frame_count = WebPDemuxGetI(dec->demux_, WEBP_FF_FRAME_COUNT);
// Note: calloc() because we fill frame with zeroes as well.
dec->curr_frame_ = (uint8_t*)WebPSafeCalloc(
dec->info_.canvas_width * NUM_CHANNELS, dec->info_.canvas_height);
if (dec->curr_frame_ == NULL) goto Error;
dec->prev_frame_disposed_ = (uint8_t*)WebPSafeCalloc(
dec->info_.canvas_width * NUM_CHANNELS, dec->info_.canvas_height);
if (dec->prev_frame_disposed_ == NULL) goto Error;
WebPAnimDecoderReset(dec);
return dec;
Error:
WebPAnimDecoderDelete(dec);
return NULL;
}
int WebPAnimDecoderGetInfo(const WebPAnimDecoder* dec, WebPAnimInfo* info) {
if (dec == NULL || info == NULL) return 0;
*info = dec->info_;
return 1;
}
// Returns true if the frame covers the full canvas.
static int IsFullFrame(int width, int height, int canvas_width,
int canvas_height) {
return (width == canvas_width && height == canvas_height);
}
// Clear the canvas to transparent.
static int ZeroFillCanvas(uint8_t* buf, uint32_t canvas_width,
uint32_t canvas_height) {
const uint64_t size =
(uint64_t)canvas_width * canvas_height * NUM_CHANNELS * sizeof(*buf);
if (!CheckSizeOverflow(size)) return 0;
memset(buf, 0, (size_t)size);
return 1;
}
// Clear given frame rectangle to transparent.
static void ZeroFillFrameRect(uint8_t* buf, int buf_stride, int x_offset,
int y_offset, int width, int height) {
int j;
assert(width * NUM_CHANNELS <= buf_stride);
buf += y_offset * buf_stride + x_offset * NUM_CHANNELS;
for (j = 0; j < height; ++j) {
memset(buf, 0, width * NUM_CHANNELS);
buf += buf_stride;
}
}
// Copy width * height pixels from 'src' to 'dst'.
static int CopyCanvas(const uint8_t* src, uint8_t* dst,
uint32_t width, uint32_t height) {
const uint64_t size = (uint64_t)width * height * NUM_CHANNELS;
if (!CheckSizeOverflow(size)) return 0;
assert(src != NULL && dst != NULL);
memcpy(dst, src, (size_t)size);
return 1;
}
// Returns true if the current frame is a key-frame.
static int IsKeyFrame(const WebPIterator* const curr,
const WebPIterator* const prev,
int prev_frame_was_key_frame,
int canvas_width, int canvas_height) {
if (curr->frame_num == 1) {
return 1;
} else if ((!curr->has_alpha || curr->blend_method == WEBP_MUX_NO_BLEND) &&
IsFullFrame(curr->width, curr->height,
canvas_width, canvas_height)) {
return 1;
} else {
return (prev->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) &&
(IsFullFrame(prev->width, prev->height, canvas_width,
canvas_height) ||
prev_frame_was_key_frame);
}
}
// Blend a single channel of 'src' over 'dst', given their alpha channel values.
// 'src' and 'dst' are assumed to be NOT pre-multiplied by alpha.
static uint8_t BlendChannelNonPremult(uint32_t src, uint8_t src_a,
uint32_t dst, uint8_t dst_a,
uint32_t scale, int shift) {
const uint8_t src_channel = (src >> shift) & 0xff;
const uint8_t dst_channel = (dst >> shift) & 0xff;
const uint32_t blend_unscaled = src_channel * src_a + dst_channel * dst_a;
assert(blend_unscaled < (1ULL << 32) / scale);
return (blend_unscaled * scale) >> 24;
}
// Blend 'src' over 'dst' assuming they are NOT pre-multiplied by alpha.
static uint32_t BlendPixelNonPremult(uint32_t src, uint32_t dst) {
const uint8_t src_a = (src >> 24) & 0xff;
if (src_a == 0) {
return dst;
} else {
const uint8_t dst_a = (dst >> 24) & 0xff;
// This is the approximate integer arithmetic for the actual formula:
// dst_factor_a = (dst_a * (255 - src_a)) / 255.
const uint8_t dst_factor_a = (dst_a * (256 - src_a)) >> 8;
const uint8_t blend_a = src_a + dst_factor_a;
const uint32_t scale = (1UL << 24) / blend_a;
const uint8_t blend_r =
BlendChannelNonPremult(src, src_a, dst, dst_factor_a, scale, 0);
const uint8_t blend_g =
BlendChannelNonPremult(src, src_a, dst, dst_factor_a, scale, 8);
const uint8_t blend_b =
BlendChannelNonPremult(src, src_a, dst, dst_factor_a, scale, 16);
assert(src_a + dst_factor_a < 256);
return (blend_r << 0) |
(blend_g << 8) |
(blend_b << 16) |
((uint32_t)blend_a << 24);
}
}
// Blend 'num_pixels' in 'src' over 'dst' assuming they are NOT pre-multiplied
// by alpha.
static void BlendPixelRowNonPremult(uint32_t* const src,
const uint32_t* const dst, int num_pixels) {
int i;
for (i = 0; i < num_pixels; ++i) {
const uint8_t src_alpha = (src[i] >> 24) & 0xff;
if (src_alpha != 0xff) {
src[i] = BlendPixelNonPremult(src[i], dst[i]);
}
}
}
// Individually multiply each channel in 'pix' by 'scale'.
static WEBP_INLINE uint32_t ChannelwiseMultiply(uint32_t pix, uint32_t scale) {
uint32_t mask = 0x00FF00FF;
uint32_t rb = ((pix & mask) * scale) >> 8;
uint32_t ag = ((pix >> 8) & mask) * scale;
return (rb & mask) | (ag & ~mask);
}
// Blend 'src' over 'dst' assuming they are pre-multiplied by alpha.
static uint32_t BlendPixelPremult(uint32_t src, uint32_t dst) {
const uint8_t src_a = (src >> 24) & 0xff;
return src + ChannelwiseMultiply(dst, 256 - src_a);
}
// Blend 'num_pixels' in 'src' over 'dst' assuming they are pre-multiplied by
// alpha.
static void BlendPixelRowPremult(uint32_t* const src, const uint32_t* const dst,
int num_pixels) {
int i;
for (i = 0; i < num_pixels; ++i) {
const uint8_t src_alpha = (src[i] >> 24) & 0xff;
if (src_alpha != 0xff) {
src[i] = BlendPixelPremult(src[i], dst[i]);
}
}
}
// Returns two ranges (<left, width> pairs) at row 'canvas_y', that belong to
// 'src' but not 'dst'. A point range is empty if the corresponding width is 0.
static void FindBlendRangeAtRow(const WebPIterator* const src,
const WebPIterator* const dst, int canvas_y,
int* const left1, int* const width1,
int* const left2, int* const width2) {
const int src_max_x = src->x_offset + src->width;
const int dst_max_x = dst->x_offset + dst->width;
const int dst_max_y = dst->y_offset + dst->height;
assert(canvas_y >= src->y_offset && canvas_y < (src->y_offset + src->height));
*left1 = -1;
*width1 = 0;
*left2 = -1;
*width2 = 0;
if (canvas_y < dst->y_offset || canvas_y >= dst_max_y ||
src->x_offset >= dst_max_x || src_max_x <= dst->x_offset) {
*left1 = src->x_offset;
*width1 = src->width;
return;
}
if (src->x_offset < dst->x_offset) {
*left1 = src->x_offset;
*width1 = dst->x_offset - src->x_offset;
}
if (src_max_x > dst_max_x) {
*left2 = dst_max_x;
*width2 = src_max_x - dst_max_x;
}
}
int WebPAnimDecoderGetNext(WebPAnimDecoder* dec,
uint8_t** buf_ptr, int* timestamp_ptr) {
WebPIterator iter;
uint32_t width;
uint32_t height;
int is_key_frame;
int timestamp;
BlendRowFunc blend_row;
if (dec == NULL || buf_ptr == NULL || timestamp_ptr == NULL) return 0;
if (!WebPAnimDecoderHasMoreFrames(dec)) return 0;
width = dec->info_.canvas_width;
height = dec->info_.canvas_height;
blend_row = dec->blend_func_;
// Get compressed frame.
if (!WebPDemuxGetFrame(dec->demux_, dec->next_frame_, &iter)) {
return 0;
}
timestamp = dec->prev_frame_timestamp_ + iter.duration;
// Initialize.
is_key_frame = IsKeyFrame(&iter, &dec->prev_iter_,
dec->prev_frame_was_keyframe_, width, height);
if (is_key_frame) {
if (!ZeroFillCanvas(dec->curr_frame_, width, height)) {
goto Error;
}
} else {
if (!CopyCanvas(dec->prev_frame_disposed_, dec->curr_frame_,
width, height)) {
goto Error;
}
}
// Decode.
{
const uint8_t* in = iter.fragment.bytes;
const size_t in_size = iter.fragment.size;
const uint32_t stride = width * NUM_CHANNELS; // at most 25 + 2 bits
const uint64_t out_offset = (uint64_t)iter.y_offset * stride +
(uint64_t)iter.x_offset * NUM_CHANNELS; // 53b
const uint64_t size = (uint64_t)iter.height * stride; // at most 25 + 27b
WebPDecoderConfig* const config = &dec->config_;
WebPRGBABuffer* const buf = &config->output.u.RGBA;
if ((size_t)size != size) goto Error;
buf->stride = (int)stride;
buf->size = (size_t)size;
buf->rgba = dec->curr_frame_ + out_offset;
if (WebPDecode(in, in_size, config) != VP8_STATUS_OK) {
goto Error;
}
}
// During the decoding of current frame, we may have set some pixels to be
// transparent (i.e. alpha < 255). However, the value of each of these
// pixels should have been determined by blending it against the value of
// that pixel in the previous frame if blending method of is WEBP_MUX_BLEND.
if (iter.frame_num > 1 && iter.blend_method == WEBP_MUX_BLEND &&
!is_key_frame) {
if (dec->prev_iter_.dispose_method == WEBP_MUX_DISPOSE_NONE) {
int y;
// Blend transparent pixels with pixels in previous canvas.
for (y = 0; y < iter.height; ++y) {
const size_t offset =
(iter.y_offset + y) * width + iter.x_offset;
blend_row((uint32_t*)dec->curr_frame_ + offset,
(uint32_t*)dec->prev_frame_disposed_ + offset, iter.width);
}
} else {
int y;
assert(dec->prev_iter_.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND);
// We need to blend a transparent pixel with its value just after
// initialization. That is, blend it with:
// * Fully transparent pixel if it belongs to prevRect <-- No-op.
// * The pixel in the previous canvas otherwise <-- Need alpha-blending.
for (y = 0; y < iter.height; ++y) {
const int canvas_y = iter.y_offset + y;
int left1, width1, left2, width2;
FindBlendRangeAtRow(&iter, &dec->prev_iter_, canvas_y, &left1, &width1,
&left2, &width2);
if (width1 > 0) {
const size_t offset1 = canvas_y * width + left1;
blend_row((uint32_t*)dec->curr_frame_ + offset1,
(uint32_t*)dec->prev_frame_disposed_ + offset1, width1);
}
if (width2 > 0) {
const size_t offset2 = canvas_y * width + left2;
blend_row((uint32_t*)dec->curr_frame_ + offset2,
(uint32_t*)dec->prev_frame_disposed_ + offset2, width2);
}
}
}
}
// Update info of the previous frame and dispose it for the next iteration.
dec->prev_frame_timestamp_ = timestamp;
WebPDemuxReleaseIterator(&dec->prev_iter_);
dec->prev_iter_ = iter;
dec->prev_frame_was_keyframe_ = is_key_frame;
CopyCanvas(dec->curr_frame_, dec->prev_frame_disposed_, width, height);
if (dec->prev_iter_.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
ZeroFillFrameRect(dec->prev_frame_disposed_, width * NUM_CHANNELS,
dec->prev_iter_.x_offset, dec->prev_iter_.y_offset,
dec->prev_iter_.width, dec->prev_iter_.height);
}
++dec->next_frame_;
// All OK, fill in the values.
*buf_ptr = dec->curr_frame_;
*timestamp_ptr = timestamp;
return 1;
Error:
WebPDemuxReleaseIterator(&iter);
return 0;
}
int WebPAnimDecoderHasMoreFrames(const WebPAnimDecoder* dec) {
if (dec == NULL) return 0;
return (dec->next_frame_ <= (int)dec->info_.frame_count);
}
void WebPAnimDecoderReset(WebPAnimDecoder* dec) {
if (dec != NULL) {
dec->prev_frame_timestamp_ = 0;
WebPDemuxReleaseIterator(&dec->prev_iter_);
memset(&dec->prev_iter_, 0, sizeof(dec->prev_iter_));
dec->prev_frame_was_keyframe_ = 0;
dec->next_frame_ = 1;
}
}
const WebPDemuxer* WebPAnimDecoderGetDemuxer(const WebPAnimDecoder* dec) {
if (dec == NULL) return NULL;
return dec->demux_;
}
void WebPAnimDecoderDelete(WebPAnimDecoder* dec) {
if (dec != NULL) {
WebPDemuxReleaseIterator(&dec->prev_iter_);
WebPDemuxDelete(dec->demux_);
WebPSafeFree(dec->curr_frame_);
WebPSafeFree(dec->prev_frame_disposed_);
WebPSafeFree(dec);
}
}