private static void BackwardReferencesHashChainFollowChosenPath(ReadOnlySpan <uint> bgra, int cacheBits, Span <ushort> chosenPath, int chosenPathSize, Vp8LHashChain hashChain, Vp8LBackwardRefs backwardRefs)
{
bool useColorCache = cacheBits > 0;
var colorCache = new ColorCache();
int i = 0;
if (useColorCache)
{
colorCache.Init(cacheBits);
}
backwardRefs.Refs.Clear();
for (int ix = 0; ix < chosenPathSize; ix++)
{
int len = chosenPath[ix];
if (len != 1)
{
int offset = hashChain.FindOffset(i);
backwardRefs.Add(PixOrCopy.CreateCopy((uint)offset, (ushort)len));
if (useColorCache)
{
for (int k = 0; k < len; k++)
{
colorCache.Insert(bgra[i + k]);
}
}
i += len;
}
else
{
PixOrCopy v;
int idx = useColorCache ? colorCache.Contains(bgra[i]) : -1;
if (idx >= 0)
{
// useColorCache is true and color cache contains bgra[i]
// Push pixel as a color cache index.
v = PixOrCopy.CreateCacheIdx(idx);
}
else
{
if (useColorCache)
{
colorCache.Insert(bgra[i]);
}
v = PixOrCopy.CreateLiteral(bgra[i]);
}
backwardRefs.Add(v);
i++;
}
}
}
private static void BackwardReferencesRle(int xSize, int ySize, ReadOnlySpan <uint> bgra, int cacheBits, Vp8LBackwardRefs refs)
{
int pixelCount = xSize * ySize;
bool useColorCache = cacheBits > 0;
var colorCache = new ColorCache();
if (useColorCache)
{
colorCache.Init(cacheBits);
}
refs.Refs.Clear();
// Add first pixel as literal.
AddSingleLiteral(bgra[0], useColorCache, colorCache, refs);
int i = 1;
while (i < pixelCount)
{
int maxLen = LosslessUtils.MaxFindCopyLength(pixelCount - i);
int rleLen = LosslessUtils.FindMatchLength(bgra.Slice(i), bgra.Slice(i - 1), 0, maxLen);
int prevRowLen = i < xSize ? 0 : LosslessUtils.FindMatchLength(bgra.Slice(i), bgra.Slice(i - xSize), 0, maxLen);
if (rleLen >= prevRowLen && rleLen >= MinLength)
{
refs.Add(PixOrCopy.CreateCopy(1, (ushort)rleLen));
// We don't need to update the color cache here since it is always the
// same pixel being copied, and that does not change the color cache state.
i += rleLen;
}
else if (prevRowLen >= MinLength)
{
refs.Add(PixOrCopy.CreateCopy((uint)xSize, (ushort)prevRowLen));
if (useColorCache)
{
for (int k = 0; k < prevRowLen; ++k)
{
colorCache.Insert(bgra[i + k]);
}
}
i += prevRowLen;
}
else
{
AddSingleLiteral(bgra[i], useColorCache, colorCache, refs);
i++;
}
}
}
/// <summary>
/// Update (in-place) backward references for the specified cacheBits.
/// </summary>
private static void BackwardRefsWithLocalCache(ReadOnlySpan <uint> bgra, int cacheBits, Vp8LBackwardRefs refs)
{
int pixelIndex = 0;
var colorCache = new ColorCache();
colorCache.Init(cacheBits);
for (int idx = 0; idx < refs.Refs.Count; idx++)
{
PixOrCopy v = refs.Refs[idx];
if (v.IsLiteral())
{
uint bgraLiteral = v.BgraOrDistance;
int ix = colorCache.Contains(bgraLiteral);
if (ix >= 0)
{
// Color cache contains bgraLiteral
v.Mode = PixOrCopyMode.CacheIdx;
v.BgraOrDistance = (uint)ix;
v.Len = 1;
}
else
{
colorCache.Insert(bgraLiteral);
}
pixelIndex++;
}
else
{
// refs was created without local cache, so it can not have cache indexes.
for (int k = 0; k < v.Len; ++k)
{
colorCache.Insert(bgra[pixelIndex++]);
}
}
}
}
private static void BackwardReferencesLz77(int xSize, int ySize, ReadOnlySpan <uint> bgra, int cacheBits, Vp8LHashChain hashChain, Vp8LBackwardRefs refs)
{
int iLastCheck = -1;
bool useColorCache = cacheBits > 0;
int pixCount = xSize * ySize;
var colorCache = new ColorCache();
if (useColorCache)
{
colorCache.Init(cacheBits);
}
refs.Refs.Clear();
for (int i = 0; i < pixCount;)
{
// Alternative #1: Code the pixels starting at 'i' using backward reference.
int j;
int offset = hashChain.FindOffset(i);
int len = hashChain.FindLength(i);
if (len >= MinLength)
{
int lenIni = len;
int maxReach = 0;
int jMax = i + lenIni >= pixCount ? pixCount - 1 : i + lenIni;
// Only start from what we have not checked already.
iLastCheck = i > iLastCheck ? i : iLastCheck;
// We know the best match for the current pixel but we try to find the
// best matches for the current pixel AND the next one combined.
// The naive method would use the intervals:
// [i,i+len) + [i+len, length of best match at i+len)
// while we check if we can use:
// [i,j) (where j<=i+len) + [j, length of best match at j)
for (j = iLastCheck + 1; j <= jMax; j++)
{
int lenJ = hashChain.FindLength(j);
int reach = j + (lenJ >= MinLength ? lenJ : 1); // 1 for single literal.
if (reach > maxReach)
{
len = j - i;
maxReach = reach;
if (maxReach >= pixCount)
{
break;
}
}
}
}
else
{
len = 1;
}
// Go with literal or backward reference.
if (len == 1)
{
AddSingleLiteral(bgra[i], useColorCache, colorCache, refs);
}
else
{
refs.Add(PixOrCopy.CreateCopy((uint)offset, (ushort)len));
if (useColorCache)
{
for (j = i; j < i + len; j++)
{
colorCache.Insert(bgra[j]);
}
}
}
i += len;
}
}
private static void BackwardReferencesHashChainDistanceOnly(
int xSize,
int ySize,
MemoryAllocator memoryAllocator,
ReadOnlySpan <uint> bgra,
int cacheBits,
Vp8LHashChain hashChain,
Vp8LBackwardRefs refs,
IMemoryOwner <ushort> distArrayBuffer)
{
int pixCount = xSize * ySize;
bool useColorCache = cacheBits > 0;
int literalArraySize = WebpConstants.NumLiteralCodes + WebpConstants.NumLengthCodes + (cacheBits > 0 ? 1 << cacheBits : 0);
var costModel = new CostModel(literalArraySize);
int offsetPrev = -1;
int lenPrev = -1;
double offsetCost = -1;
int firstOffsetIsConstant = -1; // initialized with 'impossible' value.
int reach = 0;
var colorCache = new ColorCache();
if (useColorCache)
{
colorCache.Init(cacheBits);
}
costModel.Build(xSize, cacheBits, refs);
using var costManager = new CostManager(memoryAllocator, distArrayBuffer, pixCount, costModel);
Span <float> costManagerCosts = costManager.Costs.GetSpan();
Span <ushort> distArray = distArrayBuffer.GetSpan();
// We loop one pixel at a time, but store all currently best points to non-processed locations from this point.
distArray[0] = 0;
// Add first pixel as literal.
AddSingleLiteralWithCostModel(bgra, colorCache, costModel, 0, useColorCache, 0.0f, costManagerCosts, distArray);
for (int i = 1; i < pixCount; i++)
{
float prevCost = costManagerCosts[i - 1];
int offset = hashChain.FindOffset(i);
int len = hashChain.FindLength(i);
// Try adding the pixel as a literal.
AddSingleLiteralWithCostModel(bgra, colorCache, costModel, i, useColorCache, prevCost, costManagerCosts, distArray);
// If we are dealing with a non-literal.
if (len >= 2)
{
if (offset != offsetPrev)
{
int code = DistanceToPlaneCode(xSize, offset);
offsetCost = costModel.GetDistanceCost(code);
firstOffsetIsConstant = 1;
costManager.PushInterval(prevCost + offsetCost, i, len);
}
else
{
// Instead of considering all contributions from a pixel i by calling:
// costManager.PushInterval(prevCost + offsetCost, i, len);
// we optimize these contributions in case offsetCost stays the same
// for consecutive pixels. This describes a set of pixels similar to a
// previous set (e.g. constant color regions).
if (firstOffsetIsConstant != 0)
{
reach = i - 1 + lenPrev - 1;
firstOffsetIsConstant = 0;
}
if (i + len - 1 > reach)
{
int lenJ = 0;
int j;
for (j = i; j <= reach; j++)
{
int offsetJ = hashChain.FindOffset(j + 1);
lenJ = hashChain.FindLength(j + 1);
if (offsetJ != offset)
{
lenJ = hashChain.FindLength(j);
break;
}
}
// Update the cost at j - 1 and j.
costManager.UpdateCostAtIndex(j - 1, false);
costManager.UpdateCostAtIndex(j, false);
costManager.PushInterval(costManagerCosts[j - 1] + offsetCost, j, lenJ);
reach = j + lenJ - 1;
}
}
}
costManager.UpdateCostAtIndex(i, true);
offsetPrev = offset;
lenPrev = len;
}
}
