using System;

using System.Runtime.InteropServices;

using System.Threading.Tasks;

using BCnEncoder.Shared;

namespace BCnEncoder.Encoder

{

internal class Bc2BlockEncoder : IBcBlockEncoder

{

public byte[] Encode(RawBlock4X4Rgba32[] blocks, int blockWidth, int blockHeight, EncodingQuality quality, bool parallel)

{

byte[] outputData = new byte[blockWidth * blockHeight * Marshal.SizeOf<Bc2Block>()];

Span<Bc2Block> outputBlocks = MemoryMarshal.Cast<byte, Bc2Block>(outputData);

if (parallel)

{

Parallel.For(0, blocks.Length, i =>

{

Span<Bc2Block> outputBlocks = MemoryMarshal.Cast<byte, Bc2Block>(outputData);

outputBlocks[i] = EncodeBlock(blocks[i], quality);

});

}

else

{

for (int i = 0; i < blocks.Length; i++)

{

outputBlocks[i] = EncodeBlock(blocks[i], quality);

}

}

return outputData;

}

private Bc2Block EncodeBlock(RawBlock4X4Rgba32 block, EncodingQuality quality)

{

switch (quality)

{

case EncodingQuality.Fast:

return Bc2BlockEncoderFast.EncodeBlock(block);

case EncodingQuality.Balanced:

return Bc2BlockEncoderBalanced.EncodeBlock(block);

case EncodingQuality.BestQuality:

return Bc2BlockEncoderSlow.EncodeBlock(block);

default:

throw new ArgumentOutOfRangeException(nameof(quality), quality, null);

}

}

public GlInternalFormat GetInternalFormat()

{

return GlInternalFormat.GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;

}

public GLFormat GetBaseInternalFormat()

{

return GLFormat.GL_RGBA;

}

public DXGI_FORMAT GetDxgiFormat() {

return DXGI_FORMAT.DXGI_FORMAT_BC2_UNORM;

}

#region Encoding private stuff

private static Bc2Block TryColors(RawBlock4X4Rgba32 rawBlock, ColorRgb565 color0, ColorRgb565 color1, out float error, float rWeight = 0.3f, float gWeight = 0.6f, float bWeight = 0.1f)

{

Bc2Block output = new Bc2Block();

var pixels = rawBlock.AsSpan;

output.color0 = color0;

output.color1 = color1;

var c0 = color0.ToColorRgb24();

var c1 = color1.ToColorRgb24();

ReadOnlySpan<ColorRgb24> colors = stackalloc ColorRgb24[] {

c0,

c1,

c0 * (2.0 / 3.0) + c1 * (1.0 / 3.0),

c0 * (1.0 / 3.0) + c1 * (2.0 / 3.0)

};

error = 0;

for (int i = 0; i < 16; i++)

{

var color = pixels[i];

output.SetAlpha(i, color.A);

output[i] = ColorChooser.ChooseClosestColor4(colors, color, rWeight, gWeight, bWeight, out var e);

error += e;

}

return output;

}

#endregion

#region Encoders

private static class Bc2BlockEncoderFast

{

internal static Bc2Block EncodeBlock(RawBlock4X4Rgba32 rawBlock)

{

var pixels = rawBlock.AsSpan;

PcaVectors.Create(pixels, out var mean, out var principalAxis);

PcaVectors.GetMinMaxColor565(pixels, mean, principalAxis, out var min, out var max);

ColorRgb565 c0 = max;

ColorRgb565 c1 = min;

var output = TryColors(rawBlock, c0, c1, out var _);

return output;

}

}

private static class Bc2BlockEncoderBalanced {

private const int maxTries = 24 * 2;

private const float errorThreshold = 0.05f;

internal static Bc2Block EncodeBlock(RawBlock4X4Rgba32 rawBlock)

{

var pixels = rawBlock.AsSpan;

PcaVectors.Create(pixels, out System.Numerics.Vector3 mean, out System.Numerics.Vector3 pa);

PcaVectors.GetMinMaxColor565(pixels, mean, pa, out var min, out var max);

var c0 = max;

var c1 = min;

Bc2Block best = TryColors(rawBlock, c0, c1, out float bestError);

for (int i = 0; i < maxTries; i++) {

var (newC0, newC1) = ColorVariationGenerator.Variate565(c0, c1, i);

var block = TryColors(rawBlock, newC0, newC1, out var error);

if (error < bestError)

{

best = block;

bestError = error;

c0 = newC0;

c1 = newC1;

}

if (bestError < errorThreshold) {

break;

}

}

return best;

}

}

private static class Bc2BlockEncoderSlow

{

private const int maxTries = 9999;

private const float errorThreshold = 0.01f;

internal static Bc2Block EncodeBlock(RawBlock4X4Rgba32 rawBlock)

{

var pixels = rawBlock.AsSpan;

PcaVectors.Create(pixels, out System.Numerics.Vector3 mean, out System.Numerics.Vector3 pa);

PcaVectors.GetMinMaxColor565(pixels, mean, pa, out var min, out var max);

var c0 = max;

var c1 = min;

if (c0.data < c1.data)

{

var c = c0;

c0 = c1;

c1 = c;

}

Bc2Block best = TryColors(rawBlock, c0, c1, out float bestError);

int lastChanged = 0;

for (int i = 0; i < maxTries; i++) {

var (newC0, newC1) = ColorVariationGenerator.Variate565(c0, c1, i);

if (newC0.data < newC1.data)

{

var c = newC0;

newC0 = newC1;

newC1 = c;

}

var block = TryColors(rawBlock, newC0, newC1, out var error);

lastChanged++;

if (error < bestError)

{

best = block;

bestError = error;

c0 = newC0;

c1 = newC1;

lastChanged = 0;

}

if (bestError < errorThreshold || lastChanged > ColorVariationGenerator.VarPatternCount) {

break;

}

}

return best;

}

}

#endregion

}

}