using System;

using System.Runtime.InteropServices;

using BCnEncoder.Shared.Colors;

namespace BCnEncoder.Shared

{

/// <summary>

/// Calculate the bounding box of rgb values as described in

/// "Real-Time DXT Compression by J.M.P. van Waveren, 2006, Id Software, Inc." and

/// "Real-Time YCoCg-DXT Compression J.M.P. van Waveren, Ignacio Castaño id Software, Inc. NVIDIA Corp."

/// </summary>

internal static class RgbBoundingBox

{

public static void Create565(ReadOnlySpan<ColorRgba32> colors, out ColorB5G6R5Packed min, out ColorB5G6R5Packed max)

{

const int colorInsetShift = 4;

const int c5655Mask = 0xF8;

const int c5656Mask = 0xFC;

int minR = 255,

minG = 255,

minB = 255;

int maxR = 0,

maxG = 0,

maxB = 0;

for (var i = 0; i < colors.Length; i++)

{

var c = colors[i];

if (c.r < minR) minR = c.r;

if (c.g < minG) minG = c.g;

if (c.b < minB) minB = c.b;

if (c.r > maxR) maxR = c.r;

if (c.g > maxG) maxG = c.g;

if (c.b > maxB) maxB = c.b;

}

var insetR = (maxR - minR) >> colorInsetShift;

var insetG = (maxG - minG) >> colorInsetShift;

var insetB = (maxB - minB) >> colorInsetShift;

// Inset by 1/16th

minR = ((minR << colorInsetShift) + insetR) >> colorInsetShift;

minG = ((minG << colorInsetShift) + insetG) >> colorInsetShift;

minB = ((minB << colorInsetShift) + insetB) >> colorInsetShift;

maxR = ((maxR << colorInsetShift) - insetR) >> colorInsetShift;

maxG = ((maxG << colorInsetShift) - insetG) >> colorInsetShift;

maxB = ((maxB << colorInsetShift) - insetB) >> colorInsetShift;

minR = minR >= 0 ? minR : 0;

minG = minG >= 0 ? minG : 0;

minB = minB >= 0 ? minB : 0;

maxR = maxR <= 255 ? maxR : 255;

maxG = maxG <= 255 ? maxG : 255;

maxB = maxB <= 255 ? maxB : 255;

// Optimal rounding

minR = (minR & c5655Mask) | (minR >> 5);

minG = (minG & c5656Mask) | (minG >> 6);

minB = (minB & c5655Mask) | (minB >> 5);

maxR = (maxR & c5655Mask) | (maxR >> 5);

maxG = (maxG & c5656Mask) | (maxG >> 6);

maxB = (maxB & c5655Mask) | (maxB >> 5);

min = new ColorB5G6R5Packed((byte)minR, (byte)minG, (byte)minB);

max = new ColorB5G6R5Packed((byte)maxR, (byte)maxG, (byte)maxB);

}

public static void Create565AlphaCutoff(ReadOnlySpan<ColorRgba32> colors, out ColorB5G6R5Packed min, out ColorB5G6R5Packed max, int alphaCutoff = 128)

{

const int colorInsetShift = 4;

const int c5655Mask = 0xF8;

const int c5656Mask = 0xFC;

int minR = 255,

minG = 255,

minB = 255;

int maxR = 0,

maxG = 0,

maxB = 0;

for (var i = 0; i < colors.Length; i++)

{

var c = colors[i];

if (c.a < alphaCutoff) continue;

if (c.r < minR) minR = c.r;

if (c.g < minG) minG = c.g;

if (c.b < minB) minB = c.b;

if (c.r > maxR) maxR = c.r;

if (c.g > maxG) maxG = c.g;

if (c.b > maxB) maxB = c.b;

}

var insetR = (maxR - minR) >> colorInsetShift;

var insetG = (maxG - minG) >> colorInsetShift;

var insetB = (maxB - minB) >> colorInsetShift;

minR = ((minR << colorInsetShift) + insetR) >> colorInsetShift;

minG = ((minG << colorInsetShift) + insetG) >> colorInsetShift;

minB = ((minB << colorInsetShift) + insetB) >> colorInsetShift;

maxR = ((maxR << colorInsetShift) - insetR) >> colorInsetShift;

maxG = ((maxG << colorInsetShift) - insetG) >> colorInsetShift;

maxB = ((maxB << colorInsetShift) - insetB) >> colorInsetShift;

minR = minR >= 0 ? minR : 0;

minG = minG >= 0 ? minG : 0;

minB = minB >= 0 ? minB : 0;

maxR = maxR <= 255 ? maxR : 255;

maxG = maxG <= 255 ? maxG : 255;

maxB = maxB <= 255 ? maxB : 255;

minR = (minR & c5655Mask) | (minR >> 5);

minG = (minG & c5656Mask) | (minG >> 6);

minB = (minB & c5655Mask) | (minB >> 5);

maxR = (maxR & c5655Mask) | (maxR >> 5);

maxG = (maxG & c5656Mask) | (maxG >> 6);

maxB = (maxB & c5655Mask) | (maxB >> 5);

min = new ColorB5G6R5Packed((byte)minR, (byte)minG, (byte)minB);

max = new ColorB5G6R5Packed((byte)maxR, (byte)maxG, (byte)maxB);

}

public static void Create565A(ReadOnlySpan<ColorRgba32> colors, out ColorB5G6R5Packed min, out ColorB5G6R5Packed max, out byte minAlpha, out byte maxAlpha)

{

const int colorInsetShift = 4;

const int alphaInsetShift = 5;

const int c5655Mask = 0xF8;

const int c5656Mask = 0xFC;

int minR = 255,

minG = 255,

minB = 255,

minA = 255;

int maxR = 0,

maxG = 0,

maxB = 0,

maxA = 0;

for (var i = 0; i < colors.Length; i++)

{

var c = colors[i];

if (c.r < minR) minR = c.r;

if (c.g < minG) minG = c.g;

if (c.b < minB) minB = c.b;

if (c.a < minA) minA = c.a;

if (c.r > maxR) maxR = c.r;

if (c.g > maxG) maxG = c.g;

if (c.b > maxB) maxB = c.b;

if (c.a > maxA) maxA = c.a;

}

var insetR = (maxR - minR) >> colorInsetShift;

var insetG = (maxG - minG) >> colorInsetShift;

var insetB = (maxB - minB) >> colorInsetShift;

var insetA = (maxA - minA) >> alphaInsetShift;

minR = ((minR << colorInsetShift) + insetR) >> colorInsetShift;

minG = ((minG << colorInsetShift) + insetG) >> colorInsetShift;

minB = ((minB << colorInsetShift) + insetB) >> colorInsetShift;

minA = ((minA << alphaInsetShift) + insetA) >> alphaInsetShift;

maxR = ((maxR << colorInsetShift) - insetR) >> colorInsetShift;

maxG = ((maxG << colorInsetShift) - insetG) >> colorInsetShift;

maxB = ((maxB << colorInsetShift) - insetB) >> colorInsetShift;

maxA = ((maxA << alphaInsetShift) - insetA) >> alphaInsetShift;

minR = minR >= 0 ? minR : 0;

minG = minG >= 0 ? minG : 0;

minB = minB >= 0 ? minB : 0;

minA = minA >= 0 ? minA : 0;

maxR = maxR <= 255 ? maxR : 255;

maxG = maxG <= 255 ? maxG : 255;

maxB = maxB <= 255 ? maxB : 255;

maxA = maxA <= 255 ? maxA : 255;

minR = (minR & c5655Mask) | (minR >> 5);

minG = (minG & c5656Mask) | (minG >> 6);

minB = (minB & c5655Mask) | (minB >> 5);

maxR = (maxR & c5655Mask) | (maxR >> 5);

maxG = (maxG & c5656Mask) | (maxG >> 6);

maxB = (maxB & c5655Mask) | (maxB >> 5);

min = new ColorB5G6R5Packed((byte)minR, (byte)minG, (byte)minB);

max = new ColorB5G6R5Packed((byte)maxR, (byte)maxG, (byte)maxB);

minAlpha = (byte)minA;

maxAlpha = (byte)maxA;

}

/// <summary>

/// Hdr rgb bounding box inset by Krzysztof Narkowicz. https://github.com/knarkowicz/GPURealTimeBC6H

/// Code is public domain.

/// </summary>

private static void InsetHdrChannel(ReadOnlySpan<ColorRgbaFloat> colors, int channel, ref float blockMax, ref float blockMin)

{

var offset = 0f;

if (blockMin < 0)

{

offset = -blockMin;

blockMin += offset;

blockMax += offset;

}

float Select(ReadOnlySpan<float> span, int i)

{

return span[i * 4 + channel] + offset;

}

var floats = MemoryMarshal.Cast<ColorRgbaFloat, float>(colors);

var refinedBlockMin = blockMax;

var refinedBlockMax = blockMin;

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

{

refinedBlockMin = MathF.Min(refinedBlockMin, Select(floats, i) == blockMin ? refinedBlockMin : Select(floats, i));

refinedBlockMax = MathF.Max(refinedBlockMax, Select(floats, i) == blockMax ? refinedBlockMax : Select(floats, i));

}

var logRefinedBlockMax = MathF.Log(refinedBlockMax + 1.0f, 2);

var logRefinedBlockMin = MathF.Log(refinedBlockMin + 1.0f, 2);

var logBlockMax = MathF.Log(blockMax + 1.0f, 2);

var logBlockMin = MathF.Log(blockMin + 1.0f, 2);

var logBlockMaxExt = (logBlockMax - logBlockMin) * (1.0f / 32.0f);

logBlockMin += MathF.Min(logRefinedBlockMin - logBlockMin, logBlockMaxExt);

logBlockMax -= MathF.Min(logBlockMax - logRefinedBlockMax, logBlockMaxExt);

blockMin = MathF.Pow(2, logBlockMin) - 1.0f - offset;

blockMax = MathF.Pow(2, logBlockMax) - 1.0f - offset;

}

public static void CreateFloat(ReadOnlySpan<ColorRgbaFloat> colors, out ColorRgbaFloat min, out ColorRgbaFloat max)

{

float minR = float.MaxValue,

minG = float.MaxValue,

minB = float.MaxValue,

minA = float.MaxValue;

float maxR = float.MinValue,

maxG = float.MinValue,

maxB = float.MinValue,

maxA = float.MinValue;

for (var i = 0; i < colors.Length; i++)

{

var c = colors[i];

if (c.r < minR) minR = c.r;

if (c.g < minG) minG = c.g;

if (c.b < minB) minB = c.b;

if (c.a < minA) minA = c.a;

if (c.r > maxR) maxR = c.r;

if (c.g > maxG) maxG = c.g;

if (c.b > maxB) maxB = c.b;

if (c.b > maxA) maxA = c.a;

}

InsetHdrChannel(colors, 0, ref maxR, ref minR);

InsetHdrChannel(colors, 1, ref maxG, ref minG);

InsetHdrChannel(colors, 2, ref maxB, ref minB);

InsetHdrChannel(colors, 3, ref maxA, ref minA);

min = new ColorRgbaFloat(minR, minG, minB, minA);

max = new ColorRgbaFloat(maxR, maxG, maxB, maxA);

}

}

}