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Create a WebPAnimDecoder API.

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This is designed for the simple use-case where one wants to decode all
frames one-by-one in order.

Also, use this API in anim_util library, which is in turn used by
anim_diff tool.

Change-Id: Ie8b653c04e867d40fd23321b3dd41b87689656c7
This commit is contained in:
Urvang Joshi
2015-09-02 16:20:24 -07:00
parent 03fb75221c
commit d39dc8f3cc
8 changed files with 501 additions and 213 deletions
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2
src/demux/Makefile.am
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@ -1,7 +1,7 @@
lib_LTLIBRARIES = libwebpdemux.la
libwebpdemux_la_SOURCES =
libwebpdemux_la_SOURCES += demux.c
libwebpdemux_la_SOURCES += anim_decode.c demux.c
libwebpdemuxinclude_HEADERS =
libwebpdemuxinclude_HEADERS += ../webp/demux.h

351
src/demux/anim_decode.c Normal file
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@ -0,0 +1,351 @@
// 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 "../webp/config.h"
#endif
#include <assert.h>
#include <string.h>
#include "../utils/utils.h"
#include "../webp/decode.h"
#include "../webp/demux.h"
#define NUM_CHANNELS 4
struct WebPAnimDecoder {
WebPDemuxer* demux_; // Demuxer created from given WebP bitstream.
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).
};
WebPAnimDecoder* WebPAnimDecoderNewInternal(const WebPData* webp_data,
int abi_version) {
WebPAnimDecoder* dec = NULL;
if (webp_data == NULL ||
WEBP_ABI_IS_INCOMPATIBLE(abi_version, WEBP_DEMUX_ABI_VERSION)) {
return NULL;
}
// Note: calloc() so that the pointer members are initialized to NULL.
dec = (WebPAnimDecoder*)WebPSafeCalloc(1ULL, sizeof(*dec));
if (dec == NULL) 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);
{
const int canvas_bytes =
dec->info_.canvas_width * NUM_CHANNELS * dec->info_.canvas_height;
// Note: calloc() because we fill frame with zeroes as well.
dec->curr_frame_ = WebPSafeCalloc(1ULL, canvas_bytes);
if (dec->curr_frame_ == NULL) goto Error;
dec->prev_frame_disposed_ = WebPSafeCalloc(1ULL, canvas_bytes);
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 void ZeroFillCanvas(uint8_t* rgba, uint32_t canvas_width,
uint32_t canvas_height) {
memset(rgba, 0, canvas_width * NUM_CHANNELS * canvas_height);
}
// Clear given frame rectangle to transparent.
static void ZeroFillFrameRect(uint8_t* rgba, int rgba_stride, int x_offset,
int y_offset, int width, int height) {
int j;
assert(width * NUM_CHANNELS <= rgba_stride);
rgba += y_offset * rgba_stride + x_offset * NUM_CHANNELS;
for (j = 0; j < height; ++j) {
memset(rgba, 0, width * NUM_CHANNELS);
rgba += rgba_stride;
}
}
// Copy width * height pixels from 'src' to 'dst'.
static void CopyCanvas(const uint8_t* src, uint8_t* dst,
uint32_t width, uint32_t height) {
assert(src != NULL && dst != NULL);
memcpy(dst, src, width * NUM_CHANNELS * height);
}
// 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.
static uint8_t BlendChannel(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 BlendPixel(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 =
BlendChannel(src, src_a, dst, dst_factor_a, scale, 0);
const uint8_t blend_g =
BlendChannel(src, src_a, dst, dst_factor_a, scale, 8);
const uint8_t blend_b =
BlendChannel(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);
}
}
// 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;
}
}
// Blend 'num_pixels' in 'src' over 'dst'.
static void BlendPixelRow(uint32_t* const src, const uint32_t* const dst,
int num_pixels) {
int i;
for (i = 0; i < num_pixels; ++i) {
uint32_t* const src_pixel_ptr = &src[i];
const uint8_t src_alpha = (*src_pixel_ptr >> 24) & 0xff;
if (src_alpha != 0xff) {
const uint32_t dst_pixel = dst[i];
*src_pixel_ptr = BlendPixel(*src_pixel_ptr, dst_pixel);
}
}
}
int WebPAnimDecoderGetNext(WebPAnimDecoder* dec,
uint8_t** rgba_ptr, int* timestamp_ptr) {
WebPIterator iter;
uint32_t width;
uint32_t height;
int is_key_frame;
int timestamp;
if (dec == NULL || rgba_ptr == NULL || timestamp_ptr == NULL) return 0;
if (!WebPAnimDecoderHasMoreFrames(dec)) return 0;
width = dec->info_.canvas_width;
height = dec->info_.canvas_height;
// 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) {
ZeroFillCanvas(dec->curr_frame_, width, height);
} else {
CopyCanvas(dec->prev_frame_disposed_, dec->curr_frame_, width, height);
}
// Decode.
{
const uint8_t* input = iter.fragment.bytes;
const size_t input_size = iter.fragment.size;
const size_t output_offset =
(iter.y_offset * width + iter.x_offset) * NUM_CHANNELS;
uint8_t* output = dec->curr_frame_ + output_offset;
const int output_stride = NUM_CHANNELS * width;
const size_t output_size = output_stride * iter.height;
if (WebPDecodeRGBAInto(input, input_size, output, output_size,
output_stride) == NULL) {
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;
BlendPixelRow((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;
BlendPixelRow((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;
BlendPixelRow((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;
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.
*rgba_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;
memset(&dec->prev_iter_, 0, sizeof(dec->prev_iter_));
dec->prev_frame_was_keyframe_ = 0;
dec->next_frame_ = 1;
}
}
void WebPAnimDecoderDelete(WebPAnimDecoder* dec) {
if (dec != NULL) {
WebPDemuxDelete(dec->demux_);
WebPSafeFree(dec->curr_frame_);
WebPSafeFree(dec->prev_frame_disposed_);
WebPSafeFree(dec);
}
}