static int EncodeLossless(const uint8_t* const data, int width, int height,
int effort_level, // in [0..6] range
VP8BitWriter* const bw,
WebPAuxStats* const stats) {
int ok = 0;
WebPConfig config;
WebPPicture picture;
VP8LBitWriter tmp_bw;
WebPPictureInit(&picture);
picture.width = width;
picture.height = height;
picture.use_argb = 1;
picture.stats = stats;
if (!WebPPictureAlloc(&picture)) return 0;
// Transfer the alpha values to the green channel.
{
int i, j;
uint32_t* dst = picture.argb;
const uint8_t* src = data;
for (j = 0; j < picture.height; ++j) {
for (i = 0; i < picture.width; ++i) {
dst[i] = (src[i] << 8) | 0xff000000u;
}
src += width;
dst += picture.argb_stride;
}
}
WebPConfigInit(&config);
config.lossless = 1;
config.method = effort_level; // impact is very small
// Set moderate default quality setting for alpha. Higher qualities (80 and
// above) could be very slow.
config.quality = 10.f + 15.f * effort_level;
if (config.quality > 100.f) config.quality = 100.f;
ok = VP8LBitWriterInit(&tmp_bw, (width * height) >> 3);
ok = ok && (VP8LEncodeStream(&config, &picture, &tmp_bw) == VP8_ENC_OK);
WebPPictureFree(&picture);
if (ok) {
const uint8_t* const data = VP8LBitWriterFinish(&tmp_bw);
const size_t data_size = VP8LBitWriterNumBytes(&tmp_bw);
VP8BitWriterAppend(bw, data, data_size);
}
VP8LBitWriterDestroy(&tmp_bw);
return ok && !bw->error_;
}
// This function always returns an initialized 'bw' object, even upon error.
static int EncodeAlphaInternal(const uint8_t* const data, int width, int height,
int method, int filter, int reduce_levels,
int effort_level, // in [0..6] range
uint8_t* const tmp_alpha,
FilterTrial* result) {
int ok = 0;
const uint8_t* alpha_src;
WebPFilterFunc filter_func;
uint8_t header;
const size_t data_size = width * height;
const uint8_t* output = NULL;
size_t output_size = 0;
VP8LBitWriter tmp_bw;
assert((uint64_t)data_size == (uint64_t)width * height); // as per spec
assert(filter >= 0 && filter < WEBP_FILTER_LAST);
assert(method >= ALPHA_NO_COMPRESSION);
assert(method <= ALPHA_LOSSLESS_COMPRESSION);
assert(sizeof(header) == ALPHA_HEADER_LEN);
// TODO(skal): have a common function and #define's to validate alpha params.
filter_func = WebPFilters[filter];
if (filter_func != NULL) {
filter_func(data, width, height, width, tmp_alpha);
alpha_src = tmp_alpha;
} else {
alpha_src = data;
}
if (method != ALPHA_NO_COMPRESSION) {
ok = VP8LBitWriterInit(&tmp_bw, data_size >> 3);
ok = ok && EncodeLossless(alpha_src, width, height, effort_level,
&tmp_bw, &result->stats);
if (ok) {
output = VP8LBitWriterFinish(&tmp_bw);
output_size = VP8LBitWriterNumBytes(&tmp_bw);
if (output_size > data_size) {
// compressed size is larger than source! Revert to uncompressed mode.
method = ALPHA_NO_COMPRESSION;
VP8LBitWriterDestroy(&tmp_bw);
}
} else {
VP8LBitWriterDestroy(&tmp_bw);
return 0;
}
}