Bitmap Fonts

The format

Version 1.1 Version 1.2

Example #1: Inside BMF

Example #2: tablo attributes

For this example, let addSpace = 1, sizeOver = –8. The initial [x, y] of the layout is not the top-left corner of the first char's bitmap, it lies on the baseline. It should be the layout routine to add (usually negative) font's sizeOver to the y-coordinate. In the picture, 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, 17);
version = buffer[4];
if (substr(buffer, 0, 4) != "\xE1\xE6\xD5\x1A" || (version != 0x11 && version != 0x12)) {
  exit('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 = 1; i <= numColors * 3; i++) {
  palette[i] *= 4; // stretch 0..63 values to 0..255
}
titleLength = fread(file, 1);
title = fread(file, titleLength);
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]) {
    tablo[whichChar][5] = fread(file, bitmapSize);
  }
}
if (version >= 0x12) { // 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]) {
      tablo[whichChar][5] = fread(file, bitmapSize);
    }
  }
  numKerningPairs = fread(file, 4);
  kerningPairs = [];
  for (i = 0; i < numKerningPairs; i++) {
    fread(file, kerningPair, 10);
    kerningPairs []= kerningPair;
  }
}
fclose(file);

Pseudocode for layout/output

text = "EXAMPLE ABC";
originalX = cursorX = 30;
cursorY = 20;
lineBreaksEnabled = true;
for (index = 0; index < strlen(text); index++) { // for each character..
  whichChar = ord(text[index]);
  if (lineBreaksEnabled && (whichChar == 13)) { // line break
    cursorY += font.lineHeight;
    cursorX = originalX;
    continue;
  }
  charWidth = font.tablo[whichChar][0];
  charHeight = font.tablo[whichChar][1];
  charRelX = font.tablo[whichChar][2];
  charRelY = font.tablo[whichChar][3];
  charShift = font.tablo[whichChar][4];
  charBitmap = font.tablo[whichChar][5];
  for (bitmapY = 0; bitmapY < charHeight; bitmapY++) { // for each bitmap row..
    for (bitmapX = 0; bitmapX < charWidth; bitmapX++) { // for each bitmap column..
      colorAttribute = charBitmap[bitmapY * charWidth + bitmapX];
      if (colorAttribute) { // leave color attribute 0 as transparent
        setPixel(
          cursorX + charRelX + bitmapX, // x
          cursorY + font.sizeOver + charRelY + bitmapY, // y
          font.palette[colorAttribute]
        );
      }
    }
  }
  cursorX += charShift + font.addSpace; // update cursor position
  if (version >= 0x12 && index < strlen(text) - 1) {
    cursorX += font.kerningPairs[whichChar, ord(text[index + 1])];
  }
}