How do you make a 'homing missile'?

[icrls984]

I've seen some scenes on algobox with homing 'missiles'. I also want to make one but I don't know any scripting. Could someone please help? Thanks

[racergonemad]

There are a few ways of going about this. The simplest way would be to just make a script that makes the velocity vector of your "missile", proportional to the relative vector between the position of the object and your target (in these examples, the mouse). Add the following code in postStep in the script menu:

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(e)=>{
    e.this.vel := [(app.mousePos(0) - e.this.pos(0)), (app.mousePos(1) - e.this.pos(1))]
}

Another, more complicated but more physically realistic way to do this is to add the following code to your missile body where it says postStep:

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(e)=>{
    (app.mousePos(0) - e.this.pos(0)) <= 0 ? {
        e.this._mouseAngle := math.pi + (math.atan((app.mousePos(1) - e.this.pos(1)) / (app.mousePos(0) - e.this.pos(0))))
    } : {
        (app.mousePos(1) - e.this.pos(1)) >= 0 ? {
            e.this._mouseAngle := math.atan((app.mousePos(1) - e.this.pos(1)) / (app.mousePos(0) - e.this.pos(0)))
        } : {
            e.this._mouseAngle := 2 * math.pi + (math.atan((app.mousePos(1) - e.this.pos(1)) / (app.mousePos(0) - e.this.pos(0))))
        }
    };
    e.this.angle <= 0 ? {
        e.this._rotation := (2 * math.pi) + e.this.angle
    } : {
        e.this._rotation := e.this.angle
    };
    (e.this._rotation - e.this._mouseAngle) >= math.pi || (e.this._rotation - e.this._mouseAngle) <= -1 * math.pi ? {
        e.this.controllerAcc := e.this._mouseAngle - e.this._rotation;
        e.this.color := [0.8, 0, 0, 1]
    } : {
        e.this.controllerAcc := e.this._rotation - e.this._mouseAngle;
        e.this.color := [0.1, 0.3, 0.5, 1]
    }
}

Next, add two thrusters on each side of the body of the missile pointing in the same direction, and in their script menus, where it says Force, add the following codes (one for each):

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{
    0.05 * (scene.entityByGeomID((readable(entity)).geom)).controllerAcc + ((math.vec.dist(app.mousePos, pos) * 0.01) - 0.001)
}

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{
    -0.05 * (scene.entityByGeomID((readable(entity)).geom)).controllerAcc + ((math.vec.dist(app.mousePos, pos) * 0.01) - 0.001)
}

Finally, go to the script menu of the body, and on top of all the parameters, right below where it says "Use at own risk!", type the following in the black box and press enter:

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_target := [0,0]

You can experiment with the constants in the Force parameters of the thrusters to get different performance results. For me, the best results are with working with a round body with about 0.1m radius, and adding a low density tail to add aerodynamic stability.

[icrls984]

Thanks!