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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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259
examples/anim_util.cc
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@ -149,237 +149,74 @@ static bool IsWebP(const std::string& file_str) {
file_str.length(), NULL, NULL) != 0;
}
// Returns true if the current frame is a key-frame.
static bool IsKeyFrameWebP(const WebPIterator& curr, const WebPIterator& prev,
const DecodedFrame* const prev_frame,
int canvas_width, int canvas_height) {
if (prev_frame == NULL) {
return true;
} else if ((!curr.has_alpha || curr.blend_method == WEBP_MUX_NO_BLEND) &&
IsFullFrame(curr.width, curr.height,
canvas_width, canvas_height)) {
return true;
} else {
return (prev.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) &&
(IsFullFrame(prev.width, prev.height, canvas_width, canvas_height) ||
prev_frame->is_key_frame);
}
}
// Blend a single channel of 'src' over 'dst', given their alpha channel values.
static uint8_t BlendChannelWebP(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 BlendPixelWebP(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;
assert(src_a + dst_factor_a < 256);
const uint8_t blend_a = src_a + dst_factor_a;
const uint32_t scale = (1UL << 24) / blend_a;
const uint8_t blend_r =
BlendChannelWebP(src, src_a, dst, dst_factor_a, scale, 0);
const uint8_t blend_g =
BlendChannelWebP(src, src_a, dst, dst_factor_a, scale, 8);
const uint8_t blend_b =
BlendChannelWebP(src, src_a, dst, dst_factor_a, scale, 16);
return (blend_r << 0) | (blend_g << 8) | (blend_b << 16) | (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 FindBlendRangeAtRowWebP(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 BlendPixelRowWebP(uint32_t* const src, const uint32_t* const dst,
int num_pixels) {
for (int 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 = BlendPixelWebP(*src_pixel_ptr, dst_pixel);
}
}
}
// Read animated WebP bitstream 'file_str' into 'AnimatedImage' struct.
static bool ReadAnimatedWebP(const char filename[], const std::string& file_str,
AnimatedImage* const image, bool dump_frames,
const char dump_folder[]) {
bool ok = true;
bool ok = false;
bool dump_ok = true;
uint32_t frame_index = 0;
int prev_frame_timestamp = 0;
const WebPData webp_data = {
reinterpret_cast<const uint8_t*>(file_str.data()), file_str.size()
};
WebPDemuxer* const demux = WebPDemux(&webp_data);
if (demux == NULL) return false;
WebPAnimDecoder* dec = WebPAnimDecoderNew(&webp_data);
if (dec == NULL) {
fprintf(stderr, "Error parsing image: %s\n", filename);
goto End;
}
WebPAnimInfo anim_info;
if (!WebPAnimDecoderGetInfo(dec, &anim_info)) {
fprintf(stderr, "Error getting global info about the animation\n");
goto End;
}
// Animation properties.
image->canvas_width = WebPDemuxGetI(demux, WEBP_FF_CANVAS_WIDTH);
image->canvas_height = WebPDemuxGetI(demux, WEBP_FF_CANVAS_HEIGHT);
image->loop_count = WebPDemuxGetI(demux, WEBP_FF_LOOP_COUNT);
image->bgcolor = WebPDemuxGetI(demux, WEBP_FF_BACKGROUND_COLOR);
const uint32_t frame_count = WebPDemuxGetI(demux, WEBP_FF_FRAME_COUNT);
const uint32_t canvas_width = image->canvas_width;
const uint32_t canvas_height = image->canvas_height;
image->canvas_width = anim_info.canvas_width;
image->canvas_height = anim_info.canvas_height;
image->loop_count = anim_info.loop_count;
image->bgcolor = anim_info.bgcolor;
// Allocate frames.
AllocateFrames(image, frame_count);
AllocateFrames(image, anim_info.frame_count);
// Decode and reconstruct frames.
WebPIterator prev_iter = WebPIterator();
WebPIterator curr_iter = WebPIterator();
for (uint32_t i = 0; i < frame_count; ++i) {
prev_iter = curr_iter;
// Get frame.
if (!WebPDemuxGetFrame(demux, i + 1, &curr_iter)) {
fprintf(stderr, "Error retrieving frame #%u\n", i);
return false;
// Decode frames.
while (WebPAnimDecoderHasMoreFrames(dec)) {
uint8_t* frame_rgba;
int timestamp;
if (!WebPAnimDecoderGetNext(dec, &frame_rgba, &timestamp)) {
fprintf(stderr, "Error decoding frame #%u\n", frame_index);
goto End;
}
DecodedFrame* const prev_frame = (i > 0) ? &image->frames[i - 1] : NULL;
uint8_t* const prev_rgba =
(prev_frame != NULL) ? prev_frame->rgba.data() : NULL;
DecodedFrame* const curr_frame = &image->frames[i];
DecodedFrame* const curr_frame = &image->frames[frame_index];
uint8_t* const curr_rgba = curr_frame->rgba.data();
curr_frame->duration = curr_iter.duration;
curr_frame->is_key_frame = IsKeyFrameWebP(curr_iter, prev_iter, prev_frame,
canvas_width, canvas_height);
// TODO(urvang): The logic of decoding and reconstructing the next animated
// frame given the previous one should be a single library call (ideally a
// user-facing API), which takes care of frame disposal, blending etc.
// Initialize.
if (curr_frame->is_key_frame) {
ZeroFillCanvas(curr_rgba, canvas_width, canvas_height);
} else {
CopyCanvas(prev_rgba, curr_rgba, canvas_width, canvas_height);
if (prev_iter.dispose_method == WEBP_MUX_DISPOSE_BACKGROUND) {
ZeroFillFrameRect(curr_rgba, canvas_width * kNumChannels,
prev_iter.x_offset, prev_iter.y_offset,
prev_iter.width, prev_iter.height);
}
}
// Decode.
const uint8_t* input = curr_iter.fragment.bytes;
const size_t input_size = curr_iter.fragment.size;
const size_t output_offset =
(curr_iter.y_offset * canvas_width + curr_iter.x_offset) * kNumChannels;
uint8_t* output = curr_rgba + output_offset;
const int output_stride = kNumChannels * canvas_width;
const size_t output_size = output_stride * curr_iter.height;
if (WebPDecodeRGBAInto(input, input_size, output, output_size,
output_stride) == NULL) {
ok = false;
break;
}
// 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 (i > 0 && curr_iter.blend_method == WEBP_MUX_BLEND &&
!curr_frame->is_key_frame) {
if (prev_iter.dispose_method == WEBP_MUX_DISPOSE_NONE) {
// Blend transparent pixels with pixels in previous canvas.
for (int y = 0; y < curr_iter.height; ++y) {
const size_t offset =
(curr_iter.y_offset + y) * canvas_width + curr_iter.x_offset;
BlendPixelRowWebP(reinterpret_cast<uint32_t*>(curr_rgba) + offset,
reinterpret_cast<uint32_t*>(prev_rgba) + offset,
curr_iter.width);
}
} else {
assert(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 (int y = 0; y < curr_iter.height; ++y) {
const int canvas_y = curr_iter.y_offset + y;
int left1, width1, left2, width2;
FindBlendRangeAtRowWebP(&curr_iter, &prev_iter, canvas_y, &left1,
&width1, &left2, &width2);
if (width1 > 0) {
const size_t offset1 = canvas_y * canvas_width + left1;
BlendPixelRowWebP(reinterpret_cast<uint32_t*>(curr_rgba) + offset1,
reinterpret_cast<uint32_t*>(prev_rgba) + offset1,
width1);
}
if (width2 > 0) {
const size_t offset2 = canvas_y * canvas_width + left2;
BlendPixelRowWebP(reinterpret_cast<uint32_t*>(curr_rgba) + offset2,
reinterpret_cast<uint32_t*>(prev_rgba) + offset2,
width2);
}
}
}
}
curr_frame->duration = timestamp - prev_frame_timestamp;
curr_frame->is_key_frame = false; // Unused.
memcpy(curr_rgba, frame_rgba,
image->canvas_width * kNumChannels * image->canvas_height);
// Needed only because we may want to compare with GIF later.
CleanupTransparentPixels(reinterpret_cast<uint32_t*>(curr_rgba),
canvas_width, canvas_height);
image->canvas_width, image->canvas_height);
if (dump_frames) {
ok = ok && DumpFrame(filename, dump_folder, i, curr_rgba,
canvas_width, canvas_height);
if (dump_frames && dump_ok) {
dump_ok = DumpFrame(filename, dump_folder, frame_index, curr_rgba,
image->canvas_width, image->canvas_height);
if (!dump_ok) { // Print error once, but continue decode loop.
fprintf(stderr, "Error dumping frames to %s\n", dump_folder);
}
}
++frame_index;
prev_frame_timestamp = timestamp;
}
WebPDemuxReleaseIterator(&prev_iter);
WebPDemuxReleaseIterator(&curr_iter);
WebPDemuxDelete(demux);
ok = dump_ok;
End:
WebPAnimDecoderDelete(dec);
return ok;
}