When not using VBO's, glVertexPointer and glTexCoordPointer do indeed take a regular void pointer. When using VBO's, this must become an offset. To be able to use the same function, without changing the function signature, it should be cast to a pointer. It doesn't need to be (char *), but can be any pointer type, as the function accepts void pointers.

So, it's not creating a pointer, it is casting an int to a pointer.

You are correct. Ignoring char* for the moment, the value 8 represents the offset pointer to the first [tx, ty] pair in your vertex array. Basically you will have to skip over the first [x, y] pair, totalling 8 bytes, to specify the starting location of your texture coordinates.

Now the char* bit is just a type cast to a pointer type, because glTexCoordPointer can be used both for VBO rendering (via glDrawElements) and for rendering primitives directly from an external memory location (via glDrawArrays).

If you are using a C compiler, you might want to use this macro to specify offsets:

glVertexPointer(2, GL_FLOAT, sizeof(Vertex), (void*)offsetof(Vertex, x)));glTexCoordPointer(2, GL_FLOAT, sizeof(Vertex), (void*)offsetof(Vertex, tx));

Hard coding offsets like you did is not always a good idea. The reason why you want to use the above method, is because there could be a remote possibility that the struct memory alignment will include some padding after the "float x, y;" declaration. Unlikely, but it might.

Another reason, what happens if you shuffle the vertex and texture coords around? Suddenly you have incorrect hard coded offsets everywhere.