Bitmap Fonts

The format

Version 1.1 Version 1.2

Example

For this example, let addSpace = 1, sizeOver = –8. The blue line is the base line, the blue cursor is the initial position to plot the text, the red cursor, being sizeOver pixels down from the base line, indicate cursor position before outputing each character of the text. Finally, to get to the actual top-left corners of each bitmap, we need to add the (relX, relY) vector from each character's tablo.

Working with the format

Pseudocode for loading a font

filename = "font.bmf";
file = fopen(filename, "rb");
buffer = fread(file, 18);
version = buffer[4];
if (substr(buffer, 0, 4) != "\xE1\xE6\xD5\x1A" || (version != 0x11 && version != 0x12)) {
  return false; // not a BMF, version 1.1 or 1.2
}
lineHeight = buffer[5];
sizeOver = buffer[6];
sizeUnder = buffer[7];
addSpace = buffer[8];
sizeInner = buffer[9];
usedColors = buffer[10];
highestColor = buffer[11];
alphaBits = buffer[12];
extraPalettes = buffer[13];
reserved = buffer[14];
numColors = buffer[16];
palette = fread(file, numColors * 3);
for (i = 0; i < numColors * 3; i++) {
  palette[i] *= 4; // stretch 0..63 values to 0..255
}
buffer = fread(file, 1); // title length
title = fread(file, buffer);
asciiChars = fread(file, 2);
for (i = 0; i < asciiChars; i++) {
  whichChar = fread(file, 1);
  tablo[whichChar] = fread(file, 5);
  if (bitmapSize = tablo[whichChar][0] * tablo[whichChar][1]) {
    bitmaps[whichChar] = fread(file, bitmapSize);
  }
}
// next goes for version 1.2 only
unicodeChars = fread(file, 4);
for (i = 0; i < unicodeChars; i++) {
  whichChar = fread(file, 4);
  tablo[whichChar] = fread(file, 5);
  if (bitmapSize = tablo[whichChar][0] * tablo[whichChar][1]) {
    bitmaps[whichChar] = fread(file, bitmapSize);
  }
}
numKerningPairs = fread(file, 4);
kerningPairs = [];
for (i = 0; i < numKerningPairs; i++) {
  fread(file, buffer, 10);
  kerningPairs []= buffer;
}
fclose(file);

Pseudocode for layout

text = "EXAMPLE ABC";
cursorX = 30;
cursorY = 20;
originalX = cursorX;
for (index = 0; index < strlen(text); index++) {
  whichChar = ord(text[index]);
  if (breakingLinesEnabled && (whichChar == 13)) {
    cursorY += font.lineHeight;
    cursorX = originalX;
    continue;
  }
  charWidth = tablo[whichChar][0];
  charHeight = tablo[whichChar][1];
  charRelX = tablo[whichChar][2];
  charRelY = tablo[whichChar][3];
  charShift = tablo[whichChar][4];
  charBitmap = tablo[whichChar][5];
  for (bitmapY = 0; bitmapY < charHeight; bitmapY++) {
    for (bitmapX = 0; bitmapX < charWidth; bitmapX++) {
      if (colorAttribute = charBitmap[bitmapY * charWidth + bitmapX]) {
        setPixel(
          cursorX + charRelX + bitmapX,
          cursorY + font.sizeOver + charRelY + bitmapY,
          font.palette[colorAttribute]
        );
      }
    }
  }
  cursorX += charShift + font.addSpace;
}