using System;

using BCnEncoder.Shared;

namespace BCnEncoder.Encoder.Bptc

{

internal static class Bc7Mode6Encoder

{

public static Bc7Block EncodeBlock(RawBlock4X4Rgba32 block, int startingVariation)

{

var hasAlpha = block.HasTransparentPixels();

var output = new Bc7Block();

Bc7EncodingHelpers.GetInitialUnscaledEndpoints(block, out var ep0, out var ep1);

var scaledEp0 =

Bc7EncodingHelpers.ScaleDownEndpoint(ep0, Bc7BlockType.Type6, false, out var pBit0);

var scaledEp1 =

Bc7EncodingHelpers.ScaleDownEndpoint(ep1, Bc7BlockType.Type6, false, out var pBit1);

ReadOnlySpan<int> partitionTable = new int[] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

const int subset = 0;

//Force 255 alpha if fully opaque

if (!hasAlpha)

{

pBit0 = 1;

pBit1 = 1;

}

Bc7EncodingHelpers.OptimizeSubsetEndpointsWithPBit(Bc7BlockType.Type6, block, ref scaledEp0,

ref scaledEp1, ref pBit0, ref pBit1, startingVariation, partitionTable, subset, hasAlpha, hasAlpha);

ep0 = Bc7EncodingHelpers.ExpandEndpoint(Bc7BlockType.Type6, scaledEp0, pBit0);

ep1 = Bc7EncodingHelpers.ExpandEndpoint(Bc7BlockType.Type6, scaledEp1, pBit1);

var indices = new byte[16];

Bc7EncodingHelpers.FillSubsetIndices(Bc7BlockType.Type6, block,

ep0,

ep1,

partitionTable, subset, indices);

if ((indices[0] & 0b1000) > 0) //If anchor index most significant bit is 1, switch endpoints

{

var c = scaledEp0;

var p = pBit0;

scaledEp0 = scaledEp1;

pBit0 = pBit1;

scaledEp1 = c;

pBit1 = p;

//redo indices

ep0 = Bc7EncodingHelpers.ExpandEndpoint(Bc7BlockType.Type6, scaledEp0, pBit0);

ep1 = Bc7EncodingHelpers.ExpandEndpoint(Bc7BlockType.Type6, scaledEp1, pBit1);

Bc7EncodingHelpers.FillSubsetIndices(Bc7BlockType.Type6, block,

ep0,

ep1,

partitionTable, subset, indices);

}

output.PackType6(new[]{

new byte[]{scaledEp0.r, scaledEp0.g, scaledEp0.b, scaledEp0.a},

new byte[]{scaledEp1.r, scaledEp1.g, scaledEp1.b, scaledEp1.a},

},

new[] { pBit0, pBit1 },

indices);

return output;

}

}

}