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using Ryujinx.Graphics.Texture.Utils;
using System;
using System.Diagnostics;
using System.Numerics;
using System.Runtime.InteropServices;
namespace Ryujinx.Graphics.Texture
{
static class BC7Decoder
{
public static void Decode(Span<byte> output, ReadOnlySpan<byte> data, int width, int height)
{
ReadOnlySpan<Block> blocks = MemoryMarshal.Cast<byte, Block>(data);
Span<uint> output32 = MemoryMarshal.Cast<byte, uint>(output);
int wInBlocks = (width + 3) / 4;
int hInBlocks = (height + 3) / 4;
for (int y = 0; y < hInBlocks; y++)
{
int y2 = y * 4;
int bh = Math.Min(4, height - y2);
for (int x = 0; x < wInBlocks; x++)
{
int x2 = x * 4;
int bw = Math.Min(4, width - x2);
DecodeBlock(blocks[y * wInBlocks + x], output32[(y2 * width + x2)..], bw, bh, width);
}
}
}
private static void DecodeBlock(Block block, Span<uint> output, int w, int h, int width)
{
int mode = BitOperations.TrailingZeroCount((byte)block.Low | 0x100);
if (mode == 8)
{
// Mode is invalid, the spec mandates that hardware fills the block with
// a transparent black color.
for (int ty = 0; ty < h; ty++)
{
int baseOffs = ty * width;
for (int tx = 0; tx < w; tx++)
{
int offs = baseOffs + tx;
output[offs] = 0;
}
}
return;
}
BC7ModeInfo modeInfo = BC67Tables.BC7ModeInfos[mode];
int offset = mode + 1;
int partition = (int)block.Decode(ref offset, modeInfo.PartitionBitCount);
int rotation = (int)block.Decode(ref offset, modeInfo.RotationBitCount);
int indexMode = (int)block.Decode(ref offset, modeInfo.IndexModeBitCount);
Debug.Assert(partition < 64);
Debug.Assert(rotation < 4);
Debug.Assert(indexMode < 2);
int endPointCount = modeInfo.SubsetCount * 2;
Span<RgbaColor32> endPoints = stackalloc RgbaColor32[endPointCount];
Span<byte> pValues = stackalloc byte[modeInfo.PBits];
endPoints.Fill(new RgbaColor32(0, 0, 0, 255));
for (int i = 0; i < endPointCount; i++)
{
endPoints[i].R = (int)block.Decode(ref offset, modeInfo.ColorDepth);
}
for (int i = 0; i < endPointCount; i++)
{
endPoints[i].G = (int)block.Decode(ref offset, modeInfo.ColorDepth);
}
for (int i = 0; i < endPointCount; i++)
{
endPoints[i].B = (int)block.Decode(ref offset, modeInfo.ColorDepth);
}
if (modeInfo.AlphaDepth != 0)
{
for (int i = 0; i < endPointCount; i++)
{
endPoints[i].A = (int)block.Decode(ref offset, modeInfo.AlphaDepth);
}
}
for (int i = 0; i < modeInfo.PBits; i++)
{
pValues[i] = (byte)block.Decode(ref offset, 1);
}
for (int i = 0; i < endPointCount; i++)
{
int pBit = -1;
if (modeInfo.PBits != 0)
{
int pIndex = (i * modeInfo.PBits) / endPointCount;
pBit = pValues[pIndex];
}
Unquantize(ref endPoints[i], modeInfo.ColorDepth, modeInfo.AlphaDepth, pBit);
}
byte[] partitionTable = BC67Tables.PartitionTable[modeInfo.SubsetCount - 1][partition];
byte[] fixUpTable = BC67Tables.FixUpIndices[modeInfo.SubsetCount - 1][partition];
Span<byte> colorIndices = stackalloc byte[16];
for (int i = 0; i < 16; i++)
{
byte subset = partitionTable[i];
int bitCount = i == fixUpTable[subset] ? modeInfo.ColorIndexBitCount - 1 : modeInfo.ColorIndexBitCount;
colorIndices[i] = (byte)block.Decode(ref offset, bitCount);
Debug.Assert(colorIndices[i] < 16);
}
Span<byte> alphaIndices = stackalloc byte[16];
if (modeInfo.AlphaIndexBitCount != 0)
{
for (int i = 0; i < 16; i++)
{
int bitCount = i != 0 ? modeInfo.AlphaIndexBitCount : modeInfo.AlphaIndexBitCount - 1;
alphaIndices[i] = (byte)block.Decode(ref offset, bitCount);
Debug.Assert(alphaIndices[i] < 16);
}
}
for (int ty = 0; ty < h; ty++)
{
int baseOffs = ty * width;
for (int tx = 0; tx < w; tx++)
{
int i = ty * 4 + tx;
RgbaColor32 color;
byte subset = partitionTable[i];
RgbaColor32 color1 = endPoints[subset * 2];
RgbaColor32 color2 = endPoints[subset * 2 + 1];
if (modeInfo.AlphaIndexBitCount != 0)
{
if (indexMode == 0)
{
color = BC67Utils.Interpolate(color1, color2, colorIndices[i], alphaIndices[i], modeInfo.ColorIndexBitCount, modeInfo.AlphaIndexBitCount);
}
else
{
color = BC67Utils.Interpolate(color1, color2, alphaIndices[i], colorIndices[i], modeInfo.AlphaIndexBitCount, modeInfo.ColorIndexBitCount);
}
}
else
{
color = BC67Utils.Interpolate(color1, color2, colorIndices[i], colorIndices[i], modeInfo.ColorIndexBitCount, modeInfo.ColorIndexBitCount);
}
if (rotation != 0)
{
int a = color.A;
switch (rotation)
{
case 1:
color.A = color.R;
color.R = a;
break;
case 2:
color.A = color.G;
color.G = a;
break;
case 3:
color.A = color.B;
color.B = a;
break;
}
}
RgbaColor8 color8 = color.GetColor8();
output[baseOffs + tx] = color8.ToUInt32();
}
}
}
private static void Unquantize(ref RgbaColor32 color, int colorDepth, int alphaDepth, int pBit)
{
color.R = UnquantizeComponent(color.R, colorDepth, pBit);
color.G = UnquantizeComponent(color.G, colorDepth, pBit);
color.B = UnquantizeComponent(color.B, colorDepth, pBit);
color.A = alphaDepth != 0 ? UnquantizeComponent(color.A, alphaDepth, pBit) : 255;
}
private static int UnquantizeComponent(int component, int bits, int pBit)
{
int shift = 8 - bits;
int value = component << shift;
if (pBit >= 0)
{
Debug.Assert(pBit <= 1);
value |= value >> (bits + 1);
value |= pBit << (shift - 1);
}
else
{
value |= value >> bits;
}
return value;
}
}
}
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