Create view (lookat) matrix for opengl manually in java

Question

I'm using JOGL and Box2d to write a simple physics based game.

But I'm struggling to create a View (LookAt) matrix. I'm trying to avoid adding any math library dependencies to project.

Could anyone share an example of how they create View matrix? So I could modify to work with my custom Matrix4f class.

Heres my method to setup orthographic projection matrix ..

public Matrix4f ortho(float left, float right, float top, float bottom, float zfar, float znear) {
    return new Matrix4f(new float[][] {
        new float[] { 2 / (right - left), 0, 0, -((right + left) / (right - left)) },
        new float[] { 0, 2 / (top - bottom), 0, -((top + bottom) / (top - bottom)) },
        new float[] { 0, 0, -2 / (zfar - znear), -((zfar + znear) / (zfar - znear)) },
        new float[] { 0, 0, 0, 1 },
    });
}

Heres my custom Matrix4f class ..

public class Matrix4f {

    public float[] values;

    public Matrix4f() {
        this.values = new float[16];
    }

    public Matrix4f(float[] values) {
        this.values = values;
    }

    public Matrix4f(float[][] values) {
        load(values);
    }

    public void load(float[][] values) {
        this.values = new float[] {
            values[0][0], values[0][1], values[0][2], values[0][3],
            values[1][0], values[1][1], values[1][2], values[1][3],
            values[2][0], values[2][1], values[2][2], values[2][3],
            values[3][0], values[3][1], values[3][2], values[3][3]
        };
    }

    public float get(int x, int y) {
        int position = x + (y * 4);
        return this.values[position];
    }

    public float[] getValues() { 
    return this.values; 
    }
}

Maybe [this question](http://stackoverflow.com/questions/349050/calculating-a-lookat-matrix) can help. — Berke Cagkan Toptas, May 08 '15 at 12:26
If using opengl, be sure to use the positive dot product on the z translation, for the sake of compatibility. — Raphael Mayer, May 10 '15 at 09:08

score 2 · Accepted Answer · answered May 10 '15 at 09:10

2

"Look at" matrix

f = normalize(target - position);
s = normalize(cross(f, up));
u = normalize(cross(s, f));

mat4 mat = mat4(1.0f);

mat.data[0] = s.x;
mat.data[4] = s.y;
mat.data[8] = s.z;

mat.data[1] = u.x;
mat.data[5] = u.y;
mat.data[9] = u.z;

mat.data[2] = -f.x;
mat.data[6] = -f.y;
mat.data[10] = -f.z;

mat.data[3] = 0.0f;
mat.data[7] = 0.0f;
mat.data[11] = 0.0f;

mat.data[12] = -dot(s, position);
mat.data[13] = -dot(u, position);
mat.data[14] = dot(f, position);
mat.data[15] = 1.0f;

answered May 10 '15 at 09:10

Raphael Mayer

667
6
19

just to confirm `(position, target, up)` are all 3-element vectors right? corresponding to what's passed to `glu.lookat` – bobbyrne01 May 11 '15 at 13:15
1

yes, the w value is not needed for this calculation – Raphael Mayer May 11 '15 at 14:07
OMG thank you, I've been fighting with this forever! – kitsu.eb Jul 10 '15 at 22:31

Create view (lookat) matrix for opengl manually in java

1 Answers1