Elysian Shadows

X Abstract X wrote:I remember I had this exact same problem the first time I made pong haha. I think what you might want to do is, not set it randomly. Instead something like this:

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speed.x = 2;
speed.y = 2;

while (gameIsRunning) {
    if (collisionWithVerticalWall)
        speed.x *= -1;

    if (collisionWithHorizontalWall)
        speed.y *= -1;
}

X Abstract X wrote:Costly does mean slow but, it's nothing you have to worry about, at all. The trig functions are just really slow relative to other operations like addition, subtraction, etc.

Not that this is an accurate test at all, but I wrote a simple program just to get an idea of the speed of things.

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float x = 0.0f;

for (float i = 0.0f; i < 10000000.0f; i++)
    x = cos(i);

This only took around 1 second to execute.

RyanPridgeon wrote:I wrote these functions which will do what you wanted and explained the steps because I'm bored. Don't just copy and paste though, read through, make sure you understand, then try it yourself. It only requires a basic knowledge of simple trigonometry and pythag. Also I didn't try compiling it so there may be mistakes.

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float getSpeed() {
  return sqrt(xVel*xVel + yVel*yVel); // use pythag theorem to work out the speed
}

float getAngle() { // returns teh angle in radians not degrees
  return atan2(yVel, xVel); // use inverse tan to calculate the angle
}

void setSpeed(float speed) {

  float currentSpeed = sqrt(xVel*xVel + yVel*yVel); // pythagorous' theorem

  if (currentSpeed > 0.0f){ // if it's not moving, then just do nothing as we dont know which direction we want to go
    xVel *= speed / currentSpeed; // this will set xVel to the correct speed.
    yVel *= speed / currentSpeed; // this will set yVel to the correct speed.
  }
}

void setDirection(float angle) { // angle in radians, not degrees

  float currentSpeed = sqrt(xVel*xVel + yVel*yVel); // pythagorous' theorem

  xVel = currentSpeed * cos(angle); // use trig with radians, with 0 angle being along the positive X, and Pi / 2 being along the positive Y
  yVel = currentSpeed * sin(angle);

}

void setVelocityPolar(float angle, float speed) { // angle in radians
  xVel = speed * cos(angle); // use trig with radians, with 0 angle being along the positive X, and Pi / 2 being along the positive Y
  yVel = speed * sin(angle);
}

If I was coding your game, I would create a vector class and use vectors to store velocity, position etc. But I guess you don't want to do that, so the above will work fine.

Avishaiozeri wrote:Thanks, i'll try that. and what do you mean 'costly' will it slow the game?

Vector2f direction(rand() % 9 - 4, rand() % 9 - 4);
direction.Normalize();
float speed = 10.0f;
position += direction * speed;

Bakkon wrote:

Avishaiozeri wrote:Thanks, i'll try that. and what do you mean 'costly' will it slow the game?

If you look up the definitions of sine and cosine, you see they are summations of a bunch of factorials and high exponentials. Extremely slower than basic addition and subtract, but on modern computers, you would notice anything unless you're calling these thousands of times per frame.

As for the topic, if you have a simple vector class, you can have your direction be a vector and then multiply it by your scalar speed.

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Vector2f direction(rand() % 9 - 4, rand() % 9 - 4);
direction.Normalize();
float speed = 10.0f;
position += direction * speed;