how to make camera follow a 3d object in opengl?

问题

i'm making a car race for the first time using opengl,the first problem i face is how to make the camera follow the car with constant distance..here is the code for keyboard function.V is the velocity of the car.

void OnSpecial(int key, int x, int y) 
{
    float step = 5;

    switch(key) {

    case GLUT_KEY_LEFTa:
        carAngle = step;
        V.z = carAngle ;
        camera.Strafe(-step/2);
        break;

    case GLUT_KEY_RIGHT:
        carAngle = -step;
        V.z = carAngle ;
        camera.Strafe(step/2);
        break;

    case GLUT_KEY_UP:
        V.x += (-step);
        camera.Walk(step/2);

        break;
    case GLUT_KEY_DOWN:
        if(V.x<0)
        {
            V.x += step;
            camera.Walk(-step/2);
        }
        break;
    }
}

回答1:

Something like that maybe ?

vec3 cameraPosition = carPosition + vec3(20*cos(carAngle), 10,20*sin(carAngle));
vec3 cameraTarget = carPosition;
vec3 cameraUp = vec3(0,1,0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity()
gluLookAt(cameraPosition, cameraTarget, cameraUp);
glTranslate(carPosition);
drawCar();

It you're not using the old and deprecated openGL API (glBegin & stuff) you'll have to do something like

mat4 ViewMatrix = LookAt(cameraPosition, cameraTarget, cameraUp); // adapt depending on what math library you use

回答2:

The answer to that is simple. You have player controlled object (car) so you have its position and orientation via ModelViewMatrix in world space (usualy pointed to the center of 3D model) To transform it to the correct follow ProjectionMatrix you must:

obtain car ModelViewMatrix to double M[16]
translate/rotate it to the new position (inside cockpit or behind car) so the Z axis is pointing the way you want to see.
Invert M ... M=Inverse(M)
Apply perspective M=M*PerspectiveMatrix
store M as ProjectionMatrix before rendering

for additional stuff you need look at my answer here: https://stackoverflow.com/a/18041433/2521214

来源：https://stackoverflow.com/questions/6171092/how-to-make-camera-follow-a-3d-object-in-opengl

标签

c++

opengl

camera

glut