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Stricter check for presence of alpha when writing lossless images

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Earlier, all lossless images were assumed to contain alpha.
Now, we use the 'alpha_is_used' bit from the VP8L bitstream to determine
the
same.

Detecting an absence of alpha can sometimes lead to much more efficient
rendering, especially for animated images.

Related: refine mux code to read width/height/has_alpha information only
once
per frame/fragment. This avoid frequent calls to VP8(L)GetInfo().

Change-Id: I4e0eef4db7d94425396c7dff6ca5599d5bca8297
This commit is contained in:
Urvang Joshi
2013-07-19 11:55:09 -07:00
parent a03c3516cb
commit 8ba1bf61a0
5 changed files with 88 additions and 98 deletions
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46
src/mux/muxread.c
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@ -76,6 +76,29 @@ static WebPMuxError ChunkVerifyAndAssign(WebPChunk* chunk,
return ChunkAssignData(chunk, &chunk_data, copy_data, GetLE32(data + 0));
}
int MuxImageFinalize(WebPMuxImage* const wpi) {
const WebPChunk* const img = wpi->img_;
const WebPData* const image = &img->data_;
const int is_lossless = (img->tag_ == kChunks[IDX_VP8L].tag);
int w, h;
int vp8l_has_alpha = 0;
const int ok = is_lossless ?
VP8LGetInfo(image->bytes, image->size, &w, &h, &vp8l_has_alpha) :
VP8GetInfo(image->bytes, image->size, image->size, &w, &h);
assert(img != NULL);
if (ok) {
// Ignore ALPH chunk accompanying VP8L.
if (is_lossless && (wpi->alpha_ != NULL)) {
ChunkDelete(wpi->alpha_);
wpi->alpha_ = NULL;
}
wpi->width_ = w;
wpi->height_ = h;
wpi->has_alpha_ = vp8l_has_alpha || (wpi->alpha_ != NULL);
}
return ok;
}
static int MuxImageParse(const WebPChunk* const chunk, int copy_data,
WebPMuxImage* const wpi) {
const uint8_t* bytes = chunk->data_.bytes;
@ -121,6 +144,7 @@ static int MuxImageParse(const WebPChunk* const chunk, int copy_data,
break;
case WEBP_CHUNK_IMAGE:
if (ChunkSetNth(&subchunk, &wpi->img_, 1) != WEBP_MUX_OK) goto Fail;
if (!MuxImageFinalize(wpi)) goto Fail;
wpi->is_partial_ = 0; // wpi is completely filled.
break;
default:
@ -218,6 +242,7 @@ WebPMux* WebPMuxCreateInternal(const WebPData* bitstream, int copy_data,
break;
case WEBP_CHUNK_IMAGE:
if (ChunkSetNth(&chunk, &wpi->img_, 1) != WEBP_MUX_OK) goto Err;
if (!MuxImageFinalize(wpi)) goto Err;
wpi->is_partial_ = 0; // wpi is completely filled.
PushImage:
// Add this to mux->images_ list.
@ -291,16 +316,17 @@ static WebPMuxError MuxGetCanvasInfo(const WebPMux* const mux,
// Check if VP8X chunk is present.
if (MuxGet(mux, IDX_VP8X, 1, &data) == WEBP_MUX_OK) {
if (data.size < VP8X_CHUNK_SIZE) return WEBP_MUX_BAD_DATA;
f = GetLE32(data.bytes);
f = GetLE32(data.bytes + 0);
w = GetLE24(data.bytes + 4) + 1;
h = GetLE24(data.bytes + 7) + 1;
} else { // Single image case.
int has_alpha;
const WebPMuxImage* const wpi = mux->images_;
WebPMuxError err = ValidateForSingleImage(mux);
if (err != WEBP_MUX_OK) return err;
err = MuxGetImageInfo(mux->images_->img_, &w, &h, &has_alpha);
if (err != WEBP_MUX_OK) return err;
if (has_alpha) f |= ALPHA_FLAG;
assert(wpi != NULL);
w = wpi->width_;
h = wpi->height_;
if (wpi->has_alpha_) f |= ALPHA_FLAG;
}
if (w * (uint64_t)h >= MAX_IMAGE_AREA) return WEBP_MUX_BAD_DATA;
@ -355,15 +381,7 @@ static WebPMuxError SynthesizeBitstream(const WebPMuxImage* const wpi,
dst = MuxEmitRiffHeader(data, size);
if (need_vp8x) {
int w, h;
WebPMuxError err;
assert(wpi->img_ != NULL);
err = MuxGetImageInfo(wpi->img_, &w, &h, NULL);
if (err != WEBP_MUX_OK) {
free(data);
return err;
}
dst = EmitVP8XChunk(dst, w, h, ALPHA_FLAG); // VP8X.
dst = EmitVP8XChunk(dst, wpi->width_, wpi->height_, ALPHA_FLAG); // VP8X.
dst = ChunkListEmit(wpi->alpha_, dst); // ALPH.
}