Matrix Orbital GLT240128 Legacy - Manual (Page 28)

Table 8: Font File Header
Nominal Width Height ASCII Start Val ASCII End Val
0x05 0x07 0x68 0x6A
Next we will have to find out how many bytes each character will use up, in order to create the character
table. The bitmaps are encoded horizontally and may have variable widths, h has a width of five, i a width
of three and j a width of four, see the figure below for an example of encoding the first letter h:
Bitmap Data Byte Hex Value
1 0 0 0 0
1 0 0 0 0 10000100 0x84
1 0 1 1 0 00101101 0x2D
1 1 0 0 1 10011000 0x98
1 0 0 0 1 11000110 0xC6
1 0 0 0 1 00100000 0x20
1 0 0 0 1
Figure 23: Bitmap Encoding
As you can see the letter h will take up five bytes with the last five bits being zero padded to form a full
byte. So if you continue the process you will get the character data as seen in table 5.1.2.
Character Data
Character Data Byte Size (For Reference)
h 0x84 0x2D 0x98 0xC6 0x20 0x05
i 0x43 0x24 0x84 0x03
j 0x2D 0x98 0x19 0x60 0x04
The second part of the font file is the character table. The character table is comprised of three bytes for
every glyph in the font file.
The first two bytes represents the position, in bytes, of the glyph stored MSB LSB referenced from the
beginning of the file (including the header. The third byte is the width of the glyph in pixels. So because
there will be 0x09 bytes in the character table (three bytes for each glyph) and four bytes in the header
section, the first entry in the table will be 13, or 0x00 0x0D in hexadecimal, and 0x05 for the width.
To calculate the second entry in the character table, representing the position and width of the second
glyph, take the offset of the first entry and add the size of the first bitmap in bytes. Since the first glyph
occupies 0x05 bytes as seen in table 5.1.2 above, and the offset is 0x00 0x0D, the offset of the second entry
will be 0x00 0x12 and the width of the glyph is 0x03.
Calculate the third entry the same way as the second to get table 9 below.
Table 9: Character Table
High Offset (MSB) Low Offset (LSB) Character Width
h 0x00 0x0D 0x05
i 0x00 0x12 0x03
j 0x00 0x15 0x04
Matrix Orbital GLT240128 23