private static Bc3Block FindAlphaValues(Bc3Block colorBlock, RawBlock4X4Rgba32 rawBlock, int variations)
{
var pixels = rawBlock.AsSpan;
//Find min and max alpha
byte minAlpha = 255;
byte maxAlpha = 0;
bool hasExtremeValues = false;
for (int i = 0; i < pixels.Length; i++)
{
if (pixels[i].A < 255 && pixels[i].A > 0)
{
if (pixels[i].A < minAlpha)
{
minAlpha = pixels[i].A;
}
if (pixels[i].A > maxAlpha)
{
maxAlpha = pixels[i].A;
}
}
else
{
hasExtremeValues = true;
}
}
int SelectAlphaIndices(ref Bc3Block block)
{
int cumulativeError = 0;
var a0 = block.Alpha0;
var a1 = block.Alpha1;
Span <byte> alphas = a0 > a1 ? stackalloc byte[] {
private static Bc3Block TryColors(RawBlock4X4Rgba32 rawBlock, ColorRgb565 color0, ColorRgb565 color1, out float error, float rWeight = 0.3f, float gWeight = 0.6f, float bWeight = 0.1f)
{
Bc3Block output = new Bc3Block();
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[i] = ColorChooser.ChooseClosestColor4(colors, color, rWeight, gWeight, bWeight, out var e);
error += e;
}
return(output);
}
internal static Bc3Block 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;
Bc3Block 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;
}
}
best = FindAlphaValues(best, rawBlock, 5);
return(best);
}
internal static Bc3Block 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;
}
Bc3Block 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;
}
}
best = FindAlphaValues(best, rawBlock, 8);
return(best);
}
