Question

I have written a 3D environment in OpenGL where you can move forward/backwards and look around (up/down left/right) However I cant work out how you can side step to the left of right.

I am using gluLookAt and my moving forward code is

GLfloat v[] = {[self centerAtIndex:0] - [self eyeAtIndex:0],[self centerAtIndex:1] - [self eyeAtIndex:1], [self centerAtIndex:2] - [self eyeAtIndex:2]}; 

[self setEye:[self eyeAtIndex:0] + v[0] * SPEED_MOVE atIndex:0];
[self setEye:[self eyeAtIndex:2] + v[2] * SPEED_MOVE atIndex:2];
[self setCenter: [self centerAtIndex:0] + v[0] * SPEED_MOVE atIndex:0];
[self setCenter: [self centerAtIndex:2] + v[2] * SPEED_MOVE atIndex:2];

and

gluLookAt(eye[0], eye[1], eye[2],center[0],  center[1], center[2], 0.0, 1, 0.0);

Anyone got any idea how to side step or seen an example?

Solution

float up[3] = {0, 1, 0};
        float forward[3] = { center[0] - eye[0],center[1] - eye[1],center[2] - eye[2] };

        float left[3];
        left[0] = forward[1] * up[2] - forward[2] * up[1];
        left[1] = forward[2] * up[0] - forward[0] * up[2];
        left[2] = forward[0] * up[1] - forward[1] * up[0];

        // now translate your eye position
        [self setEye:[self eyeAtIndex:0] - left[0] * SPEED_MOVE atIndex:0];
        [self setEye:[self eyeAtIndex:2] - left[2] * SPEED_MOVE atIndex:2];
        [self setCenter: [self centerAtIndex:0] - left[0] * SPEED_MOVE atIndex:0];
        [self setCenter: [self centerAtIndex:2] - left[2] * SPEED_MOVE atIndex:2];  


        if (([self eyeAtIndex:2] >= MapSizeZ || [self eyeAtIndex:0] >= MapSizeX  || [self eyeAtIndex:2] <= 1 || [self eyeAtIndex:0] <= 1) || [self checkCollisionWithPoint:CGPointMake([self eyeAtIndex:0] ,[self eyeAtIndex:2])] ){

            [self setEye:[self eyeAtIndex:0] + left[0] * SPEED_MOVE atIndex:0];
            [self setEye:[self eyeAtIndex:2] + left[2] * SPEED_MOVE atIndex:2];
            [self setCenter: [self centerAtIndex:0] + left[0] * SPEED_MOVE atIndex:0];
            [self setCenter: [self centerAtIndex:2] + left[2] * SPEED_MOVE atIndex:2];  
        }

Answer 1

To move sideways you simply have to translate the eye position along the camera’s right vector.

To find the right vector, remember that the cross product of two vectors gives a perpendicular vector. So, the cross product of your forward vector and your up vector will give the right vector.

Your forward vector is v[3], but I will use ‘forward’ here for clarity.

// find the Right vector. (forward cross product up)
float right[3];
right[0] = forward[1] * up[2] - forward[2] * up[1];
right[1] = forward[2] * up[0] - forward[0] * up[2];
right[2] = forward[0] * up[1] - forward[1] * up[0];

// now translate your eye position
[self setEye:[self eyeAtIndex:0] + right[0] * SPEED_MOVE atIndex:0];
[self setEye:[self eyeAtIndex:2] + right[2] * SPEED_MOVE atIndex:2];

You should also note that the glu library is not available for OpenGL ES, so you will have to reimplement the lookat function, which is straightforward, but also another question.