// Writes a 16 bit font texture.
static void WriteBgra4444(BinaryWriter writer, Bitmap bitmap)
{
writer.Write(DXGI_FORMAT_B4G4R4A4_UNORM);
writer.Write(bitmap.Width * sizeof(ushort));
writer.Write(bitmap.Height);
using (var bitmapData = new BitmapUtils.PixelAccessor(bitmap, ImageLockMode.ReadOnly)) {
for (int y = 0; y < bitmap.Height; y++)
{
for (int x = 0; x < bitmap.Width; x++)
{
Color color = bitmapData[x, y];
int r = color.R >> 4;
int g = color.G >> 4;
int b = color.B >> 4;
int a = color.A >> 4;
int packed = b | (g << 4) | (r << 8) | (a << 12);
writer.Write((ushort)packed);
}
}
}
}
// Writes an uncompressed 32 bit font texture.
static void WriteRgba32(BinaryWriter writer, Bitmap bitmap)
{
writer.Write(DXGI_FORMAT_R8G8B8A8_UNORM);
writer.Write(bitmap.Width * 4);
writer.Write(bitmap.Height);
using (var bitmapData = new BitmapUtils.PixelAccessor(bitmap, ImageLockMode.ReadOnly)) {
for (int y = 0; y < bitmap.Height; y++)
{
for (int x = 0; x < bitmap.Width; x++)
{
Color color = bitmapData[x, y];
writer.Write(color.R);
writer.Write(color.G);
writer.Write(color.B);
writer.Write(color.A);
}
}
}
}
// Writes a block compressed monochromatic font texture.
static void WriteCompressedMono(BinaryWriter writer, Bitmap bitmap, CommandLineOptions options)
{
if ((bitmap.Width & 3) != 0 ||
(bitmap.Height & 3) != 0)
{
throw new ArgumentException("Block compression requires texture size to be a multiple of 4.");
}
writer.Write(DXGI_FORMAT_BC2_UNORM);
writer.Write(bitmap.Width * 4);
writer.Write(bitmap.Height / 4);
using (var bitmapData = new BitmapUtils.PixelAccessor(bitmap, ImageLockMode.ReadOnly)) {
for (int y = 0; y < bitmap.Height; y += 4)
{
for (int x = 0; x < bitmap.Width; x += 4)
{
CompressBlock(writer, bitmapData, x, y, options);
}
}
}
}
// We want to compress our font textures, because, like, smaller is better,
// right? But a standard DXT compressor doesn't do a great job with fonts that
// are in premultiplied alpha format. Our font data is greyscale, so all of the
// RGBA channels have the same value. If one channel is compressed differently
// to another, this causes an ugly variation in brightness of the rendered text.
// Also, fonts are mostly either black or white, with grey values only used for
// antialiasing along their edges. It is very important that the black and white
// areas be accurately represented, while the precise value of grey is less
// important.
//
// Trouble is, your average DXT compressor knows nothing about these
// requirements. It will optimize to minimize a generic error metric such as
// RMS, but this will often sacrifice crisp black and white in exchange for
// needless accuracy of the antialiasing pixels, or encode RGB differently to
// alpha. UGLY!
//
// Fortunately, encoding monochrome fonts turns out to be trivial. Using DXT3,
// we can fix the end colors as black and white, which gives guaranteed exact
// encoding of the font inside and outside, plus two fractional values for edge
// antialiasing. Also, these RGB values (0, 1/3, 2/3, 1) map exactly to four of
// the possible 16 alpha values available in DXT3, so we can ensure the RGB and
// alpha channels always exactly match.
static void CompressBlock(BinaryWriter writer, BitmapUtils.PixelAccessor bitmapData, int blockX, int blockY, CommandLineOptions options)
{
long alphaBits = 0;
int rgbBits = 0;
int pixelCount = 0;
for (int y = 0; y < 4; y++)
{
for (int x = 0; x < 4; x++)
{
long alpha;
int rgb;
int value = bitmapData[blockX + x, blockY + y].A;
if (options.NoPremultiply)
{
// If we are not premultiplied, RGB is always white and we have 4 bit alpha.
alpha = value >> 4;
rgb = 0;
}
else
{
// For premultiplied encoding, quantize the source value to 2 bit precision.
if (value < 256 / 6)
{
alpha = 0;
rgb = 1;
}
else if (value < 256 / 2)
{
alpha = 5;
rgb = 3;
}
else if (value < 256 * 5 / 6)
{
alpha = 10;
rgb = 2;
}
else
{
alpha = 15;
rgb = 0;
}
}
// Add this pixel to the alpha and RGB bit masks.
alphaBits |= alpha << (pixelCount * 4);
rgbBits |= rgb << (pixelCount * 2);
pixelCount++;
}
}
// Output the alpha bit mask.
writer.Write(alphaBits);
// Output the two endpoint colors (black and white in 5.6.5 format).
writer.Write((ushort)0xFFFF);
writer.Write((ushort)0);
// Output the RGB bit mask.
writer.Write(rgbBits);
}