opengl - how to put texture on 3d irregular object

Question

I have to create animation where gatling gun will be shoot (it doesn't have to be complex, cause it's just a practice). I drew basic version of my gun which looks like this:

Don't bother colors - i made them like that to be able to see where are egdes of particular parts of gun. Now i would like to make it look better by using some texture - moro or something like metalic color - example 1 or example2. I know how to load texture and how to use it for 2d objects, but i have no idea if there is a possiblity to use this texture for my whole drawing or do i have to use texture for every part separately? This is my code which corresponds to load texture from bmp file and make it able to use:

void initTexture(string fileName)
{
    loadBmp(fileName.c_str());
    textureId = 13;
    glBindTexture(GL_TEXTURE_2D, textureId); //Tell OpenGL which texture to edit
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
    //Map the image to the texture
    glTexImage2D(GL_TEXTURE_2D,                //Always GL_TEXTURE_2D
                 0,                            //0 for now
                 GL_RGB,                       //Format OpenGL uses for image
                 tex.info.biWidth, tex.info.biHeight,  //Width and height
                 0,                            //The border of the image
                 GL_RGB, //GL_RGB, because pixels are stored in RGB format
                 GL_UNSIGNED_BYTE, //GL_UNSIGNED_BYTE, because pixels are stored
                                   //as unsigned numbers
                 tex.px);               //The actual pixel data

}

loadBmp() is function to load bitmap file. I tried to search something in the Internet and stackoverflow, but all exmaples where about cubes or spheres, which doesn't help me. How can i put texture on this drawing?

Answer 1

Texture mapping requires to (manually) assign texture coordinates to each vertex. There are some approaches on automatic texture coordinate generation, or getting away without texture coordinates, by giving each face an individual pixel (Disney Animation pioneered the later method for their computer animated films).

Since you didn't specify which program you used to model I'll refer you to some tutorials on texture UV mapping for Blender

http://wiki.blender.org/index.php/Doc:2.6/Manual/Textures/Mapping/UV/Unwrapping

Please don't tell me you did "code" your gun, because this is wrong, wrong, wrong!

Once you got the texture coordinates you pass them to OpenGL as just another vertex attribute.