/// <summary>
/// Special row-processing that only stores the alpha data.
/// </summary>
public static void ExtractAlphaRows(LosslessDecoder dec, int row)
{
int num_rows = row - dec.last_row_;
if (num_rows <= 0) return; // Nothing to be done.
dec.ApplyInverseTransforms (num_rows, dec.pixels32_, dec.width_ * dec.last_row_);
// Extract alpha (which is stored in the green plane).
int width = dec.io_.width; // the final width (!= dec->width_)
int cache_pixs = width * num_rows;
// uint8_t* const dst = (uint8_t*)dec->io_->opaque + width * dec->last_row_;
int dst = width * dec.last_row_;
int src = dec.argb_cache_;
for (int i = 0; i < cache_pixs; ++i)
dec.io_.opaque[dst+i] = (byte)(dec.pixels32_[src+i] >> 8);
dec.last_row_ = dec.last_out_row_ = row;
}
// Processes (transforms, scales & color-converts) the rows decoded after the
// last call.
static void ProcessRows(LosslessDecoder dec, int row)
{
throw new NotImplementedException ("Lossless RGB decoder not implemented");
}
bool DecodeAlphaHeader(byte[] data, int data_i, int data_size, byte[] output)
{
vp8l_dec_ = new LosslessDecoder();
vp8l_dec_.Init (width_, height_, m_io, data, data_i, data_size, output);
uint[] decoded = null;
if (!vp8l_dec_.DecodeImageStream (width_, height_, true, ref decoded, false))
return false;
// Special case: if alpha data uses only the color indexing transform and
// doesn't use color cache (a frequent case), we will use DecodeAlphaData()
// method that only needs allocation of 1 byte per pixel (alpha channel).
if (vp8l_dec_.next_transform_ == 1
&& vp8l_dec_.transforms_[0].type_ == VP8LImageTransformType.ColorIndexing
&& vp8l_dec_.Is8bOptimizable())
{
use_8b_decode_ = true;
vp8l_dec_.AllocateInternalBuffers8b();
}
else
{
// Allocate internal buffers (note that dec->width_ may have changed here).
use_8b_decode_ = false;
vp8l_dec_.AllocateInternalBuffers32b (width_);
}
return true;
}
