Change value based on difference between two angles

Question

So in my intro C++ class I'm building a game of pool. I have everything working well so far. Currently I am figuring out the angle between the two balls upon hit, sending the hit ball off at the angle of impact, and the striking ball off at the appropriate reflect angle. What I would really like is to have glancing hits impart less speed to the ball being hit, and direct hits to impart more speed. My idea that I don't know how to put into code is if the struckBall has the same end angle as the original strikerBall, then it gets something like 90% of it's speed. As the angle changes though, let's say it's 45 degrees off from original angle, then it would be around a 50/50 split of speed at their new angles.

Relevant code:

private: void checkBallCollision(BilliardBall^ striker, BilliardBall^ struck)
                {
                    if (distanceBetweenBalls(striker, struck))
                    {
                        double velocityStrike = 0;
                        double velocityStruck = 0;
                        double struckBallAngle = GetAngle(striker->Location, struck->Location);
                        double strikerBallAngle = GetAngle(struck->Location, striker->Location);
                        striker->Angle = striker->Angle;
                        if (strikerBallAngle > striker->Angle)
                        {
                            striker->Angle = striker->Angle + (1 / (strikerBallAngle - striker->Angle));
                        } 
                        else
                        {
                            striker->Angle = striker->Angle - (1 / (striker->Angle - strikerBallAngle));
                        }
                        struck->Angle = struckBallAngle;


                        double distance = GetDistance(striker->Location, struck->Location);
                        struck->PosX += (BALL_WIDTH - distance) * Math::Cos(struckBallAngle);
                        struck->PosY += (BALL_WIDTH - distance) * Math::Sin(struckBallAngle);

                        struck->Location = Point(struck->PosX, struck->PosY);

                        struck->Distance = striker->Distance * .7;
                        striker->Distance *= .2;
                    }
                }

You should make your divisions use `1.0` instead of `1`, to ensure floating point division instead of integer division. — Thomas Matthews, Mar 07 '15 at 06:05
To model pool ball collision accurately you need to use rules based on the conservation of momentum. Try googling "pool balls momentum" for some links. — Eamonn O'Brien-Strain, Mar 07 '15 at 06:39

score 1 · Answer 1 · answered Mar 07 '15 at 06:39

1

You lost me at if... That is, 'if' statements have no place in a physics problem. There is a mathematical function (a formula) that will describe this. 'If' you didn't know this already, here are a couple tips:

The two balls will move perpendicular to each other.
One ball will move perpendicular to the tangent line between the two balls, the other will move parallel.

answered Mar 07 '15 at 06:39

neurotik

1,390
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15

Physics is always explained better with pictures. – Thomas Matthews Mar 07 '15 at 17:44

score 0 · Answer 2 · edited May 23 '17 at 12:20

It is a often repeated fallacy that you need to compute the collision angle for elastic collisions. It makes for a nice geometric exploration of the situation, but the actual formula only requires the center coordinates and velocity vectors (and mass and radii) at the moment of collision, see my answer https://stackoverflow.com/a/28252655/3088138 to a similar problem or the wikipedia page on elastic collisions.

Change value based on difference between two angles

2 Answers2