OpenGL Texture Loading

Question

Evening everyone, I'm going around in circles here but I think I'm looking in the wrong places.

My question is how would I go about loading an image and applying it to a primative in openGL. For example loading a bmp or jpg and applying it to a glutsolidsphere.

Would the solution be limited to one platform or could it work across all?

Thanks for your help

Answer 1

Well, if you want to, you can write your own bmp loader. Here is the specification and some code. Otherwise, I happen to have a tga loader here. Once you do that, it will return the data in an unsigned character array, otherwise known as GL_UNSIGNED_BYTE.

To make an OpenGL texture from this array, you first define a variable that will serve as a reference to that texture in OpenGL's memory.

GLuint textureid;

Then, you need to tell OpenGL to make space for a new texture:

glGenTextures(1, &textureid);

Then, you need to bind that texture as the currently used texture.

glBindTexture(GL_TEXTURE_2D, textureid);

Finally, you need to tell OpenGL where the data is for the current texture.

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, your_data);

Then, when you render a primitive, you apply it to the primitive by calling glBindTexture again:

glBindTexture(GL_TEXTURE_2D, textureid);
glBegin(GL_QUAD);
     glTexCoord2f(0.0, 0.0);
     glVertex3f(0.0, 0.0, 0.0);
     glTexCoord2f(1.0, 0.0);
     glVertex3f(1.0, 0.0, 0.0);
     glTexCoord2f(1.0, 1.0);
     glVertex3f(1.0, 1.0, 0.0);
     glTexCoord2f(0.0, 1.0);
     glVertex3f(0.0, 1.0, 0.0);
glEnd();

However, any time you apply the texture to a primitive, you need to have texture coordinate data along with vertex data, and glutSolidSphere does not generate texture coordinate data. To texture a sphere, either generate it yourself, or call texgen functions, or use shaders.