Moving the camera as in a first person shooter

Question

I am trying to implement the movement of the camera with the mouse. The result I want to achieve is the same that you get when you move your aim in a first person shooter.

Here is the code I wrote, where "camera" is the vector which contains the location of the camera, "center" is the vector which contains the location of the point to which the camera is pointing at, and "move_vector" is simply "center" minus "camera"

    if(mouse_move_x != 0 || mouse_move_y != 0){

        float a0 = Array_norm<float>(move_vector,3);
        Array_copy<float>(move_vector,move_vector2,3);

        //perform mouse horizontal axis movement
        current_x_angle = atan2(move_vector[2],move_vector[0]);
        current_x_angle = current_x_angle + mouse_move_x * input::MOUSE_sensitivity * 0.017;

        move_vector[0] = cos(current_x_angle)*a0;
        move_vector[2] = sin(current_x_angle)*a0;

        //perform mouse vertical axis movement
        temp = sqrt(move_vector2[0]*move_vector2[0]+move_vector2[2]*move_vector2[2]);

        current_y_angle = atan2(move_vector2[1],temp);
        current_y_angle = current_y_angle - mouse_move_y * input::MOUSE_sensitivity * 0.017;

        move_vector2[1] = sin(current_y_angle)*a0;
        if(move_vector2[0]==0){
            move_vector2[2] = (move_vector2[2] >= 0) ? cos(current_y_angle)*a0 : -cos(current_y_angle)*a0;
        }
        else{
            temp2 = move_vector2[2]/move_vector2[0];
            temp = cos(current_y_angle)*a0*sqrt(1/(1+temp2*temp2));
            move_vector2[0] = (move_vector2[0] >= 0) ? temp : -temp;
            move_vector2[2] = move_vector2[0]*temp2; 
        }

        //join x and y movements
        Array_sum<float>(move_vector,move_vector2,move_vector,3);
        Array_normalize<float>(move_vector,move_vector,3);

        center[0] = move_vector[0] + camera[0];
        center[1] = move_vector[1] + camera[1];
        center[2] = move_vector[2] + camera[2];

    }

Two questions:

• the code works only when I consider only one of the due movements (either horizontal movement or vertical movement). The code does not work when I get both movements combined and I cannot understand why
• Is there a better (and more mathematically compact) approach to compute the new camera position and focus point? I am sure there is :)

Thank you

Answer 1

Well I decided to change to a much easier approach.

        float radius = Array_norm<float>(move_vector,3);
        current_y_angle = acos(move_vector[1]/radius) + mouse_move_y * input::MOUSE_sensitivity * 0.017;
        current_x_angle = atan2(move_vector[2],move_vector[0]) + mouse_move_x * input::MOUSE_sensitivity * 0.017;

        move_vector[0] = radius*cos(current_x_angle)*sin(current_y_angle);
        move_vector[2] = radius*sin(current_x_angle)*sin(current_y_angle);
        move_vector[1] = radius*cos(current_y_angle);

        center[0] = move_vector[0] + camera[0];
        center[1] = move_vector[1] + camera[1];
        center[2] = move_vector[2] + camera[2];

This code works perfectly. It is based on the idea of "Spherical coordinate system". It is perfectly explained in Wikipedia.

I found this one, it does the job and it is pretty much mathematically compact. Any other approach that you think it is worth mentioning?

Thanks