Allegro 5 al_draw_text skips characters

Question

I'm using Allegro 5.0.8 al_draw_text to draw text on a bitmap (backbuffer). However, I've noticed that the first character of the string is always skipped. Moreover, whenever the same character appears in the string, it is skipped again.

For example:

font = al_load_font(path.c_str(), 100, 0);
std::string str = "01230450678";    
al_draw_text(font, color, 100, 100, 0, str.c_str());

Will print "12345678", skipping all occurrences of '0'

I've tried several TTF fonts, which work with other graphic software. I've noticed that this sometimes may or may not happen with the same font, depending only on the text size on screen (font size)

Edit: I've formatted the code and added the arguments I've used to load the font.

Edit2: Here is a complete code to replicate this using Allegro 5.0.8.

This code should print "0123045670890", but, instead, it renders the following image: (Note: I didn't cleared the memory because the error appears before program finishes)

//---------------------------------------------------------------------------

#include <string>

#include <allegro5/allegro.h>
#include <allegro5/allegro_image.h>
#include <allegro5/allegro_opengl.h>
#include <allegro5/allegro_font.h>
#include <allegro5/allegro_ttf.h>
#include <allegro5/allegro_primitives.h>
//---------------------------------------------------------------------------


using namespace std;

//---------------------------------------------------------------------------

int main(int argc, char * argv[])
{
    al_init();
    al_install_keyboard();
    al_init_image_addon();
    al_init_primitives_addon();
    al_init_font_addon();
    al_init_ttf_addon();

    al_set_new_display_flags(ALLEGRO_OPENGL);
    ALLEGRO_DISPLAY * mainWindow= al_create_display(1200, 1000);

    ALLEGRO_PATH *path = al_get_standard_path(ALLEGRO_RESOURCES_PATH);
    string file = al_path_cstr(path, '/');
    file = file + "arial.ttf";
    ALLEGRO_FONT * font = al_load_font(file.c_str(), 50, 0);

    al_set_target_bitmap(al_get_backbuffer(mainWindow));        
    al_draw_filled_rectangle(0, 0, 1200, 1000, al_map_rgb(0,0,0));

    al_draw_text(font, al_map_rgb(255,0,0), 50, 50, 0, "0123045670890");

    al_save_bitmap("d:\\teste.bmp", al_get_backbuffer(mainWindow));

    al_flip_display();

    al_rest(5.0);

    return 0;
}

Answer 1

It sounds like a bug with caching glyphs. These sorts of glitches generally are only applicable to video memory, so if you switch to a memory bitmap font by calling this before loading the font you can work around the issue:

al_set_new_bitmap_flags(ALLEGRO_MEMORY_BITMAP);

You'll need to clear the flags after you load the font, or else all subsequent bitmaps will be software based as well.

However, this is not a good long term solution, as using memory bitmaps may significantly degrade performance.

While the above will probably get you up and running, you should at some point:

• Upgrade your OpenGL drivers if applicable
• Try out Allegro 5.1.X, as it may have fixes that have not yet made it to 5.0.X.

If neither of those solve the issue, then you should file a bug report, including the sample source code and details of your OS and video card.