Re: [AD] [patch] is_trans_font()

[Daniel Schlyder <daniel@xxxxxxxxxx>]

Milan Mimica wrote:
> I think font_has_alpha() would be just enough. It is assumed that you 
> had to determine the font type some way after load_font(). So the 
> complete float loading & conversion code can look like:
>
> FONT *fnt = load_font(...);
> FONT *agl_fnt;
>
> if (font_has_alpha(fnt))
> {
> 	make_trans_font(fnt);
> 	agl_fnt = allegro_gl_convert_allegro_font_ex(..., GL_RGBA);
> }
> else
> {
> 	agl_fnt = allegro_gl_convert_allegro_font_ex(..., GL_ALPHA8);
> }

make_trans_font() triggers an assertion when passed a font that already 
uses the trans vtable. This becomes a problem when I want to keep the 
Allegro font in memory after creating the AllegroGL copy so I can 
restore the latter faster after texture memory has been lost. Of course, 
I can use a variable to keep track of whether make_trans_font() has been 
called on the font, but that's a bit ugly, isn't it? I'd prefer either 
to have is_trans_font() or patch make_trans_font() to do nothing if the 
font is already using the trans vtable. I suppose the latter is the way 
to go since it only introduces one new API function. Then again, it 
seems natural to add is_trans_font() to complement the existing 
is_mono_font, is_color_font and is_compatible_font functions.

> It would be the best if load_font could determine the font type itself 
> and convert before returning, just like it does for monochrome and color 
> fonts. Too bad that trans font would crash on textout_ex() if trans 
> blender hasn't been set.

I'll leave it to someone more knowledgeable than me to determine if that 
is fixable. :)

Attached is a patch to add font_has_alpha().

--
Daniel Schlyder

Index: include/allegro/font.h
===================================================================
--- include/allegro/font.h	(revision 7545)
+++ include/allegro/font.h	(working copy)
@@ -41,6 +41,7 @@
    struct FONT_VTABLE *vtable;
 } FONT;
 
+AL_FUNC(int, font_has_alpha, (FONT *f));
 AL_FUNC(void, make_trans_font, (FONT *f));
 
 AL_FUNC(int, is_color_font, (FONT *f));
Index: src/font.c
===================================================================
--- src/font.c	(revision 7545)
+++ src/font.c	(working copy)
@@ -1445,6 +1445,33 @@
 
 
 
+/* font_has_alpha:
+ *  Returns TRUE if a color font has an alpha channel.
+ */
+int font_has_alpha(FONT *fnt)
+{
+   FONT_COLOR_DATA *data;
+   int ch;
+
+   ASSERT(fnt);
+
+   if (!is_color_font(fnt))
+      return FALSE;
+
+   data = (FONT_COLOR_DATA *)(fnt->data);
+
+   while (data) {
+      for (ch = data->begin; ch != data->end; ++ch)
+         if (_bitmap_has_alpha(data->bitmaps[ch - data->begin]))
+            return TRUE;
+      data = data->next;
+   }
+
+   return FALSE;
+}
+
+
+
 /* make_trans_font:
  *  Modifes a font so glyphs are drawn with draw_trans_sprite.
  */