Question

I’m working with SDL and OpenGL, creating a fairly simple application. I created a basic text rendering function, which maps a generated texture onto a quad for each character. This texture is rendered from a bitmap of each character.

The bitmap is fairly small, about 800×16 pixels. It works absolutely fine on my desktop and laptop, both in and out of a VM (and on both Windows and Linux).

Now, I’m trying it on another computer, and the text becomes all garbled – it appears as though the computer can’t handle a very basic thing like this. To see if it was due to the OS, I installed VirtualBox and tested it in the VM – but the result is even worse! Instead of rendering anything (albeit garbled), it just renders a plain white box.

Why is this occuring, and is there any way to solve it?

---

Some code – how I initialize the texture:

glGenTextures(1, &fontRef);
glBindTexture(GL_TEXTURE_2D, iFont);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, FNT_IMG_W, FNT_IMG_H, 0,
             GL_RGB, GL_UNSIGNED_BYTE, MY_FONT);

Above, MY_FONT is an unsigned char array (the raw image dump from GIMP). When I draw a character:

GLfloat ix = c * (GLfloat) FNT_CHAR_W;
// We just map each corner of the texture to a new vertex.
glTexCoord2d(ix,              FNT_CHAR_H); glVertex3d(x,          y,          0);
glTexCoord2d(ix + FNT_CHAR_W, FNT_CHAR_H); glVertex3d(x + iCharW, y,          0);
glTexCoord2d(ix + FNT_CHAR_W, 0);          glVertex3d(x + iCharW, y + iCharH, 0);
glTexCoord2d(ix,              0);          glVertex3d(x,          y + iCharH, 0);

Answer 1

That sounds to me as if the Graphics card of the machine you are working on only supports power of two textures (i.e. 16, 32, 64…). 800×16 certainly would not work on such a gfx card.

you can use glGet with ARB_texture_non_power_of_two to check if the gfx card does support it.

Or use GLEW to do that check for you.