Glyph spacing

no-reply@allegro.cc (dthompson) — Mon, 11 Dec 2017 18:27:51 +0000

I have a bitmap font and am wondering whether it's possible to get Allegro to add 1px spacing between the glyphs when rendering the font, rather than having to add 1px spacing to the right of each character in the source bitmap.

With an unkerned TTF font, I'm aware that it'd be possible to cycle through every glyph and alter its kerning value in order to achieve this.

Is this possible with the current API or will I need to render each glyph manually? In the case of the latter, could I request an al_set_bitmap_font_spacing, or perhaps an even more generic function that can apply extra letter spacing to TTF fonts too?

no-reply@allegro.cc (Edgar Reynaldo) — Mon, 11 Dec 2017 20:16:18 +0000

You can have your cake and eat it too.

Have allegro do it for you.

Use al_get_glyph. Although it takes a pair of codepoints, must be to do with the kerning. From an ALLEGRO_GLYPH* you can get the font's bitmap source rectangle for that codepoint, and then you draw it yourself. I'll whip up a quick example for you.

Actually, all you need are these two functions here :

#SelectExpand
  1int GetTextWidth(ALLEGRO_FONT* f , const char* s , int xspacing) {
 int prev = 0;
 int current = 0;
 int i = 0;
 int w = 0;
 while ((current = s[i])) {
    ALLEGRO_GLYPH g;
    memset(&g , 0 , sizeof(g));
    if (al_get_glyph(f , prev , current , &g)) {
       if (i) {
          w += xspacing;
       }
       w += g.advance;
    }
    prev = current;
    ++i;
 }
 return w;
 19}
 20
 21
 22
 23void DrawSpacedText(ALLEGRO_FONT* font , const char* str , int cx , int cy , ALLEGRO_COLOR col , int xspacing) {
 int w = GetTextWidth(font , str , xspacing);
 
 int x = cx - w/2;
 int y = cy - al_get_font_line_height(font)/2;
 int i = 0;
 int prev = 0;
 int current = 0;
 while ((current = str[i])) {
    ALLEGRO_GLYPH g;
    memset(&g , 0 , sizeof(g));
    if (al_get_glyph(font , prev , current , &g)) {
       if (g.bitmap) {
          al_draw_tinted_bitmap_region(g.bitmap , col , g.x , g.y , g.w , g.h , x , y , 0);
       }
       x += g.advance;
       x += xspacing;
    }
    prev = current;
    ++i;
 }
 
 45}

It took me about 10 minutes to add in horizontal spacing.

What you can do is take and load your bitmap font, then draw that font to a blank with the additional spacing, then save it and from now on reload the second one.

no-reply@allegro.cc (SiegeLord) — Mon, 11 Dec 2017 22:09:56 +0000

In addition to the above, we're adding support for the bmfont format, which has this padding a little more explicit. Obviously it's a new format, but I think it's a superset of the current one.

Also, there's al_draw_glyph, which might be preferable to drawing the bitmap yourself.

no-reply@allegro.cc (Edgar Reynaldo) — Mon, 11 Dec 2017 22:18:11 +0000

I came across a quirk in a ttf font I use. When I call al_get_glyph on the space character (ascii 32), it returns true, but the bitmap is null.

no-reply@allegro.cc (SiegeLord) — Tue, 12 Dec 2017 09:01:26 +0000

Edgar Reynaldo said:

I came across a quirk in a ttf font I use. When I call al_get_glyph on the space character (ascii 32), it returns true, but the bitmap is null.

That's normal. I've updated the documentation to mention this.

no-reply@allegro.cc (dthompson) — Tue, 12 Dec 2017 18:53:42 +0000

Edgar Reynaldo said:

You can have your cake and eat it too.

Nice that works well for a single line of text; reimplementing all of A5's font routines with that extra parameter might be more of a pain though...

SiegeLord said:

we're adding support for the bmfont format

This'd probably be a better solution; looking forward to it.

I'll probably just go and alter the font's image file for now; it's just a 5x5 pixel font so won't require much effort.