public void decode(ColorR5G6B5 colorOrig0, ColorR5G6B5 colorOrig1, UInt32 indices)
{
var color0 = colors[0] = colorOrig0;
var color1 = colors[1] = colorOrig1;
// Select color2 and color3 following the COMPRESSED_RGB_S3TC_DXT1_EXT spec
//
// https://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt
//
if (colorOrig0.value >= colorOrig1.value)
{
colors[2] = new Image.Color(
(2f * color0.r + color1.r) / 3f,
(2f * color0.g + color1.g) / 3f,
(2f * color0.b + color1.b) / 3f);
colors[3] = new Image.Color(
(color0.r + 2f * color1.r) / 3f,
(color0.g + 2f * color1.g) / 3f,
(color0.b + 2f * color1.b) / 3f);
}
else
{
colors[2] = new Image.Color(
(color0.r + color1.r) / 2f,
(color0.g + color1.g) / 2f,
(color0.b + color1.b) / 2f);
colors[3] = Image.Color.Black;
}
// Decode from bitarray
for(int i = 0; i < 16; i++)
{
var index = (byte)(indices & 0x3);
pixels[i] = colors[index];
indices = indices >> 2;
}
}
public void decode(ColorR5G6B5 colorOrig0, ColorR5G6B5 colorOrig1, UInt32 indices)
{
var color0 = colors[0] = colorOrig0;
var color1 = colors[1] = colorOrig1;
// Select color2 and color3 following the COMPRESSED_RGB_S3TC_DXT1_EXT spec
//
// https://www.opengl.org/registry/specs/EXT/texture_compression_s3tc.txt
//
if (colorOrig0.value >= colorOrig1.value)
{
colors[2] = new Image.Color(
(2f * color0.r + color1.r) / 3f,
(2f * color0.g + color1.g) / 3f,
(2f * color0.b + color1.b) / 3f);
colors[3] = new Image.Color(
(color0.r + 2f * color1.r) / 3f,
(color0.g + 2f * color1.g) / 3f,
(color0.b + 2f * color1.b) / 3f);
}
else
{
colors[2] = new Image.Color(
(color0.r + color1.r) / 2f,
(color0.g + color1.g) / 2f,
(color0.b + color1.b) / 2f);
colors[3] = Image.Color.Black;
}
// Decode from bitarray
for (int i = 0; i < 16; i++)
{
var index = (byte)(indices & 0x3);
pixels[i] = colors[index];
indices = indices >> 2;
}
}
public void encode()
{
// The idea is to get the most distant complementary colors in a simple way
// A simple algorithm with an O(n) function cost
var nearRed = pixels[0];
var nearGreen = pixels[0];
var nearBlue = pixels[0];
var nearYellow = pixels[0];
var nearCyan = pixels[0];
var nearMarge = pixels[0];
var nearWhite = pixels[0];
var nearBlack = pixels[0];
var distRed = startDistance;
var distGreen = startDistance;
var distBlue = startDistance;
var distYellow = startDistance;
var distCyan = startDistance;
var distMarge = startDistance;
var distWhite = startDistance;
var distBlack = startDistance;
var newDistance = startDistance;
// First we will check the closest color to each axis
foreach (var color in pixels)
{
newDistance = Image.Color.Red.distance(color);
if (newDistance < distRed)
{
nearRed = color;
distRed = newDistance;
}
newDistance = Image.Color.Green.distance(color);
if (newDistance < distGreen)
{
nearGreen = color;
distGreen = newDistance;
}
newDistance = Image.Color.Blue.distance(color);
if (newDistance < distBlue)
{
nearBlue = color;
distBlue = newDistance;
}
newDistance = Image.Color.Yellow.distance(color);
if (newDistance < distYellow)
{
nearYellow = color;
distYellow = newDistance;
}
newDistance = Image.Color.Cyan.distance(color);
if (newDistance < distCyan)
{
nearCyan = color;
distCyan = newDistance;;
}
newDistance = Image.Color.Margenta.distance(color);
if (newDistance < distMarge)
{
nearMarge = color;
distMarge = newDistance;
}
newDistance = Image.Color.White.distance(color);
if (newDistance < distWhite)
{
nearWhite = color;
distWhite = newDistance;
}
newDistance = Image.Color.Black.distance(color);
if (newDistance < distBlack)
{
nearBlack = color;
distBlack = newDistance;
}
}
// Get the most distant complementary colors
var lastDistance = nearRed.distance(nearCyan);
colors[0] = nearRed;
colors[1] = nearCyan;
newDistance = nearBlue.distance(nearYellow);
if (lastDistance < newDistance)
{
colors[0] = nearBlue;
colors[1] = nearYellow;
lastDistance = newDistance;
}
newDistance = nearGreen.distance(nearMarge);
if (lastDistance < newDistance)
{
colors[0] = nearGreen;
colors[1] = nearMarge;
}
newDistance = nearWhite.distance(nearBlack);
if (lastDistance < newDistance)
{
colors[0] = nearWhite;
colors[1] = nearBlack;
}
// By default make color0 bigger than color1, so we get
// more interpolation values
ColorR5G6B5 color_0_R5G6B5 = colors[0];
ColorR5G6B5 color_1_R5G6B5 = colors[1];
// Compare the R5G6B5 colors
if (color_0_R5G6B5.value < color_1_R5G6B5.value)
{
colors[1] = color_1_R5G6B5;
colors[0] = color_0_R5G6B5;
}
else
{
colors[0] = color_0_R5G6B5;
colors[1] = color_1_R5G6B5;
}
// Calculate the colors after the selection
colors[2] = new Image.Color(
(2f * colors[0].r + colors[1].r) / 3f,
(2f * colors[0].g + colors[1].g) / 3f,
(2f * colors[0].b + colors[1].b) / 3f);
colors[3] = new Image.Color(
(colors[0].r + 2f * colors[1].r) / 3f,
(colors[0].g + 2f * colors[1].g) / 3f,
(colors[0].b + 2f * colors[1].b) / 3f);
// For each pixel in the texel block
for (int i = 0; i < 16; i++)
{
// Select the closer color from the 4 colors
var currentColor = pixels[i];
lastDistance = currentColor.distance(colors[0]);
uint candidateColor = 0;
for (uint j = 1; j < 4; j++)
{
newDistance = currentColor.distance(colors[j]);
if (newDistance < lastDistance)
{
lastDistance = newDistance;
candidateColor = j;
}
}
// Save it in the index array
indices |= ((candidateColor & 0x3) << (i * 2));
}
}