Okay, I can grab both the camera's current position vector and direction (the direction it's pointing) vector from the modelview matrix. Assuming I have this data on each loop iteration, how do I get the camera to rotate around its current position as opposed to 0,0,0? I have been reading a lot of tutorials that say you have to rotate the direction vector by the rotation matrix used to rotate the scene so when you apply the translation, it goes in the correct direction. I think I understand that part perfectly well, as I'm able to derive the forward/back direction vector from the modelview matrix, normalize it, and add it to the translation matrix along with the speed value. I do the same for the strafe vector, which is the cross product of the fwd/back vector and the Y direction (currently -1.0).
//calculate strafe vector using cross product of Z and Y
camera_position[z] += (direction_move[z] * speed); //WS keys (fwd/back)
camera_position[x] += (direction_strafe[x] * speed); //AD keys (strafe)
//construct translation matrix
mat4x4_translate(translate, camera_position[x], 0.0, camera_position[z]); //Y is 0.0 since we never go up/down
I then multiply the translation matrix by the rotation matrix and drop the result into the modelview matrix. Problem is, when I rotate the scene, it is always rotating around 0,0,0 so when I move around, the camera always rotates around the world's origin and not its own.