Calculating ball deflection angle when colliding with paddle in brick slayer game - c++

Question

Here is my code:
void Draw()
{
int x = 59;
int y = 500;
int temp = x;
int colour;
for (int i = 0; i < 9; ++i)
{
for (int j = 0; j < 10; ++j)
{
if (i % 2 == 0)
colour = 2;
else
colour = 3;
DrawRectangle(x, y, 65, 25, colors[colour]);
x += 67;
}
x = temp;
y -= 39;
}
DrawRectangle(tempx, 0, 85, 12, colors[5]);
DrawCircle(templx, temply, 10, colors[7]);
}
// This function will be called automatically by this frequency: 1000.0 / FPS
void Animate()
{
templx +=5;
temply +=5;
/*if(templx>350)
templx-=300;
if(temply>350)
temply-=300;*/
glutPostRedisplay(); // Once again call the Draw member function
}
// This function is called whenever the arrow keys on the keyboard are pressed...
//
I am using OpenGL for this project. The function Draw() is used to print the bricks, slider, and the ball. The Animate() function is called automatically by the frequency given in the code. As it can be seen, I have incremented the values of templx and temply, but the ball goes out of screen as it crosses its limit. I have to deflect the ball if it collides with the paddle or the wall. What can I do to achieve this? All the conditions that I have used by now do not work properly.

Answer 1

So basically you would like to have a ball that is bouncing from the edges of your window. (For this answer I will ignore the slider, finding collision with the slider is very similar to finding collision with the walls).
templx and temply pair is position of your ball. I don't know what is the 3rd argument of DrawCircle function so I will assume that it is the radius. Let wwidth and wheight be width and height of a game window. Note that this magic constant 5 is, in fact, a velocity of the ball. Now ball is moving from upper left corner to lower right corner of your window. If you change 5 to -5 it will move from lower right corner to upper left corner.
Let's introduce two more variables vx and vy - velocity on x axis and velocity on y axis. The initial values will be 5 and 5. Now notice that when ball hits the right edge of the window it doesn't change its vertical velocity, it is still moving up/down but it changes its horizontal velocity from left->right to right->left. So if the vx was 5, after hitting the right edge of the window we should change it to -5.
The next problem is how to find out if we hit the edge of the window or not.
Note that the right-most point on the ball has the position templx + radius and the left-most point on the ball has the position templx - radius etc. Now to find out if we hit the wall or not we should just compare this values with window dimensions.
// check if we hit right or left edge
if (templx + radius >= wwidth || templx - radius <= 0) {
vx = -vx;
}
// check if we hit top or bottom edge
if (temply + radius >= wheight || temply - radius <= 0) {
vy = -vy;
}
// update position according to velocity
templx += vx;
temply += vy;