Loading textures with sfml for Open GL

Question

I'm looking at nehe's texturemapping tutorial and it looks a bit overly complicated for just loading a texture. Is there a way to load a texture in SFML and then use it in Open GL? I use SFML for my windowing.

Answer 1

Welcome to OpenGL, where the fast things come for free and the easy things are made hard.

If you thought that sample was long and complicated, "just for loading a texture", then you've seen nothing yet. Wait until you have to load DDS textures, process HDR textures, support cubemaps, render to a texture, etc.

Loading a texture in OpenGL consists of two components:

• Getting the data from your image format. You could load a texture from a file or generate it procedurally. It doesn't matter, as long as you end up with a nice array of color information.

• Putting the data on the videocard. The data needs to go from system RAM to video RAM.

The first part should be easy, because SFML comes with a standard image loader.

sf::Image img_data;
if (!img_data.LoadFromFile("images/avatar.png"))
{
    LOG_ERROR("Could not load '%s'.", "images/avatar.png");
    return false;
}

Next, we'll have to generate an OpenGL texture object.

GLuint texture_handle;
glGenTextures(1, &texture_handle);

There are a number of choices for binding a texture. There are the three main types: 1D, 2D and 3D and you have support for cubemaps (+X, -X, +Y, -Y, +Z, -Z). However, in 99% of the cases, you will want a 2D texture.

glBindTexture(GL_TEXTURE_2D, texture_handle);

Now we get to the interesting part. Let's upload our data to the video card.

glTexImage2D(
    GL_TEXTURE_2D, 0, GL_RGBA,
    img_data.GetWidth(), img_data.GetHeight(),
    0,
    GL_RGBA, GL_UNSIGNED_BYTE, img_data.GetPixelsPtr()
);

Finally, we can set a number of texture parameters. These answer questions like: what if we use a texture coordinate that is outside of the range (0.0, 1.0)? Do we wrap around (GL_REPEAT) or do we do nothing (GL_CLAMP)? They can also be used to explain to the videocard that we want to use linear interpolation on our textures.

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

And now you should be able to bind your texture using glBindTexture and use it to draw textured meshes.