How to create bounded bounce animation? (SFML) - c++

Question

I have to move a ball in an angle in an open SFML and keep it within the window size (Like the DVD thing), but my current function makes it to the bottom and doesn't "bounce". It slides across the bottom and stops once it reaches the other corner. The initial position is (1,1)
void Bubble::updatePosition() {
if( isTopBottom() ){
do{
_x += .1;
_y += -.2;
}while( !isTopBottom() );
}
else if( isLeftRight() ){
do{
_x += -.1;
_y += .2;
}while( !isLeftRight() );
}
else{
_x += .1;
_y += .2;
}
_bubble.setPosition(_x, _y);
}
the isLeftRight, isTopBottom are bools that check if they have reached the edges

Answer 1

Simple Solution
Use velocities and manipulate those on collision; then, use the velocity to update the position.
Check each edge separately and decide on one relevant velocity component based on that.
e.g. (following your values)
// Positions:
float x = 1.f;
float y = 1.f;
// Velocities:
float vx = 0.1f;
float vy = 0.2f;
// ... then, inside loop:
// Check collisions (and adjust velocity):
if (x < 0.f)
vx = 0.1f;
else if (x > 640.f)
vx = -0.1f;
if (y < 0.f)
vy = 0.2f;
else if (y > 640.f)
vy = -0.2f;
// update position (still inside loop):
x += vx;
y += vy;
Cleaner Solution
This is the same as the simple solution above but, since you tagged SFML, you can use SFML vectors to keep the two components together. Also modified variable names to be more clear. Pulled out the size of the window and the velocity amounts from being hard-coded into the logic as well:
const sf::Vector2f windowSize(640.f, 640.f);
const sf::Vector2f velocityAmount(0.1f, 0.2f);
sf::Vector2f position(1.f, 1.f);
sf::Vector2f velocity = velocityAmount;
// ... then, inside loop:
// Check collisions (and adjust velocity):
if (position.x < 0.f)
velocity.x = velocityAmount.x;
else if (position.x > windowSize.x)
velocity.x = -velocityAmount.x;
if (position.y < 0.f)
velocity.y = velocityAmount.y;
else if (position.y > windowSize.y)
velocity.y = -velocityAmount.y;
// update position (still inside loop):
position += velocity;
You should notice that the velocity is the values that are added to the position on each iteration of the loop and that velocity does not change when it is not considered colliding with an edge.
Initial Problem
The initial problem you had is it always moves in the same direction (towards the bottom-right) if it is not hitting an edge. This means that it'll never be allowed to rise above the bottom edge (or away from right edge).