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BMF – ByteMap font format
Version 1.1
| offset |
size |
meaning |
| 0 | 4 | magic header (0xE1E6D51A) |
| 4 | 1 | version (0x11 for v1.1) |
| 5 | 1 | line-height
should be equal to or greater than size-under – size-over |
| 6 | 1 | size-over the base line (–128…127)
measure from base line to top of capital letters, in pixels; should be negative |
| 7 | 1 | size-under the base line (–128…127)
measure from base line to lowest extends (of letters like "y", "g"), in pixels; usually positive |
| 8 | 1 | add-space after each char (–128…127)
how many pixels to add after plotting each character |
| 9 | 1 | size-inner (small letters height) (–128…127)
measure from base line to top of small letters; should be negative |
| 10 | 1 | count of used colors |
| 11 | 1 | highest used color attribute |
| 12 | 4 | reserved |
| 16 | 1 | number of colors in palette (P) |
| 17 | P*3 | font palette (RGB, 0…63 per component) |
| 17+P*3 | 1 | title length (T) |
| 18+P*3 | T | title string |
| 19+P*3+T | 2 | number of characters in font i.e. having non-zero size or shift (N) |
| 20+P*3+T | ? | ’tablo‘ - character bitmap definitions |
N * …
| offset | size | meaning |
|---|
| 0 | 1 | which character |
| 1 | 1 | character width (W) |
| 2 | 1 | character height (H) |
| 3 | 1 | relx – X offset from cursor position (–128…127) |
| 4 | 1 | rely – Y offset from cursor position (–128…127) |
| 5 | 1 | horizontal cursor shift after drawing the character |
| 6 | W * H | character bitmap (uncompressed, 8 bits per pixel) |
Character with both its size (width, height) and shift being zero is considered empty/unused and as such not stored.
Characters with empty bitmaps are also valid. For example, space usually has no bitmap but its shift parameter is important to store in the font.
Example
Let addspace = 1 for this example. The red arrow (being size-over pixels from the base line) is cursor position before outputing each character in the text.
| | F | j | : | Q |
|---|
| width | 4 | 4 | 1 | 10 |
|---|
| height | 8 | 9 | 4 | 9 |
|---|
| relx | 0 | –2 | 1 | 0 |
|---|
| rely | 0 | 2 | 2 | 0 |
|---|
| shift | 4 | 2 | 3 | 8 |
|---|
Working with the format
Pseudocode for loading a font
file = fopen("font.bmf", "rb");
buffer = fread(file, 18);
if (substr(buffer, 0, 5) != "\xE1\xE6\xD5\x1A\x11") {
return false;
}
lineHeight = buffer[5];
sizeOver = buffer[6];
sizeUnder = buffer[7];
addSpace = buffer[8];
sizeInner = buffer[9];
usedColors = buffer[10];
highestColor = buffer[11];
colors = buffer[16];
palette = fread(file, colors * 3);
for (i = 0; i < colors * 3; i++) {
palette[i] *= 4;
}
buffer = fread(file, 1);
title = fread(file, buffer);
numChars = fread(file, 1);
for (i = 0; i < numChars; i++) {
whichChar = fread(file, 1);
tablo[whichChar] = fread(file, 5);
if (bitmapSize = tablo[whichChar][0] * tablo[whichChar][1]) {
bitmaps[whichChar] = fread(file, bitmapSize);
}
}
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 += 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++) {
colorAttribute = charBitmap[bitmapY * charWidth + bitmapX];
if (colorAttribute) {
setPixel(
cursorX + charRelX + bitmapX,
cursorY + sizeOver + charRelY + bitmapY,
palette[colorAttribute]
);
}
}
}
cursorX += charShift + addSpace;
}