CODEWITHSUNDEEP
c++openglsdltexturestexture-mapping
Breakthrough
Breakthrough

Reputation: 2534

Why is my texture rendered improperly in my OpenGL application?

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 800x16 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);

Upvotes: 1

Views: 285

Answers (1)

moka
moka

Reputation: 4501

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...). 800x16 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.

Upvotes: 2

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