Working with SVGAlib Fonts

What Is a Font?

Fonts don't have the ability to display themselves. Most fonts are contained within data files, which are then called by executables. (These data files are often in binary format, which means that they can't be read by a text editor).

Types of Fonts

A scalable font, on the other hand, is stored in the same manner as a vectored graphic. Rather than being mapped pixel by pixel, a scalable font's "stylistic information" is saved in its data file. This information includes the angles of each character's curves, and how they're proportioned. Because no actual picture exists, it's up to the program that reads in the font to construct it for display. This adds some processing overhead, but the end result is well worth it. Scalable fonts can be resized without losing any quality, and often have smooth (or antialiased) edges. Now, have a look at the next diagram for an example of a scalable font. It's quite nice, isn't it? This is Arial, a TrueType font.

Bitmapped Fonts

Here's how you prepare a bitmapped font for use, using gl_font8x8:

void *font = malloc(256 * FONT_WIDTH * FONT_HEIGHT * BYTESPERPIXEL);
gl_expandfont(FONT_WIDTH, FONT_HEIGHT, COLOR, gl_font8x8, font);
gl_setfont(FONT_WIDTH, FONT_HEIGHT, font);

This loads SVGAlib's one internal font, gl_font8x8, into memory. The "8x8" means that each character in the font is eight pixels high by eight pixels across. That means you'll need to define

<font color="0000EE">FONT_HEIGHT</font>

<font color="0000EE">FONT_WIDTH</font>

<font color="0000EE">COLOR</font>

<font color="0000EE">BYTESPERPIXEL</font>

The next step is to actually display your words on the screen. This is accomplished with gl_write():

gl_write(10, 10, "Hello, world.");

The first two arguments (10 and 10) place the words on the screen -- they refer to the x and y corrdinates of the upper left-hand corner of the first character.

Here's a complete program, using the four commands you just learned:

#include 
#include 
#include 

#define FONT_HEIGHT 8
#define FONT_WIDTH 8

void prepare_font(void);

int main(void)
{
int x = 10,
y = 10;

char text[] = "Hello, world!";

vga_init();
vga_setmode(G320x200x256);
gl_setcontextvga(G320x200x256);

prepare_font();
gl_write(x, y, text);

vga_getch();

vga_setmode(TEXT);

return 0;
}

void prepare_font(void)
{
int color = 15; /* white */

void *font = malloc(256 * FONT_WIDTH * FONT_HEIGHT * BYTESPERPIXEL);
gl_expandfont(FONT_WIDTH, FONT_HEIGHT, color, gl_font8x8, font);
gl_setfont(FONT_WIDTH, FONT_HEIGHT, font);
}

Upon running this program, you should see the words "Hello, world!" displayed in white at the top of the screen. Hooray! You've done it. Feel free to play around -- for example, try varying the placement of your text by providing different x and y values to gl_write().

It's worth noting that gl_writen(int x, int y, int n, char *s) is identical to gl_write(), except that it only displays the first "n" characters of your string.

Should you choose to include your string directly in gl_write() or gl_writen(), you'll have to terminate it with "\0" like so:

gl_write(10, 10, "Hello, World!\0");

If you don't, you won't see any results.

Different Fonts

unsigned char font01[2048] =
{
124,130,186,162,186,130,124,0,126,129,165,129,165,153,129,126,
126,129,165,129,153,165,129,126,108,246,246,254,124,56,16,0,
16,56,124,254,124,56,16,0,16,56,84,254,84,16,56,0,
56,124,254,254,108,16,56,0,16,24,20,20,48,112,96,0,
254,254,254,238,254,254,254,0,236,138,138,170,170,170,236,0,
142,136,136,140,136,136,232,0,174,170,170,234,170,170,174,0,
238,136,136,204,136,136,136,0,238,138,138,142,140,138,234,0,
62,34,62,34,102,238,204,0,16,84,40,198,40,84,16,0,
240,248,252,254,252,248,240,0,30,62,126,254,126,62,30,0,
16,56,124,16,124,56,16,0,238,238,238,238,238,0,238,0,

...

48,48,48,240,0,0,0,0,0,0,0,255,0,0,0,0,
24,24,24,31,0,0,0,0,24,24,24,24,24,24,24,24,
136,34,136,34,136,34,136,34,85,170,85,170,85,170,85,170,
68,170,68,170,68,170,68,170,51,102,204,153,51,102,204,153,
204,102,51,153,204,102,51,153,199,143,31,62,124,248,241,227,
227,241,248,124,62,31,143,199,174,128,186,2,234,8,171,32
}

(I went ahead and eliminated some of the lines for brevity). A full font array will have information for 256 characters. Each character contained in an 8 x 8 font is comprised of eight numbers, which means that a complete 8 x 8 font has 2048 numeric values (256 * 8 = 2048).

To use a "char" font, simply substitute "gl_font8x8" with the name of your char array, like so:

gl_expandfont(WIDTH, HEIGHT, color, font01, font);

Finding Bitmapped Fonts

You can find this font, and more, at the official SVGAlib website: www.svgalib.org