Inverting an angle on the Y-axis, X works - c++

Question

I've asked this question over at GameDev but got not response so far and this question is a bit time sensitive unfortunately.
I'm pretty sure this is just me doing something stupid or not understanding something that I should but I cannot figure out what is wrong here.
I'm having a problem bouncing a projectile off a sprite, we've been asked to move the projectile using the equations of motions which makes things a little more difficult but as far as I can see what I have should work.
What I'm trying to do is change the angle of the collided projectile depending on which direction it is coming from.
Here is a video that is hopefully not too laggy for you to see what is happening:
Link
When the projectile collides with the left or right hand side of the sprite everything works as expected, it just switches X direction.
When it hit's the top or bottom of the sprite however it doesn't change, it just sort of rolls along the top and the shoots off.
Here is the movement code:
float nX = get_x() + cos(nGetAngle() * 3.14 / 180) * getU() * getT();
float nY = get_y() - sin(nGetAngle() * 3.14 / 180) * getU() * getT() + 0.5 * 9.8 * getT() * getT();
set_world_position(nX, nY);
Where U is initial velocity, T is time and nGetAngle() is the angle in degrees (which is set to radians whenever the angle is set).
Here is my collision for the top of the player:
//if the projectile is colliding in any way with the player sprite
if (projectiles[currProj]->get_y() < player->get_y()) // top of player
{
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(-vy, vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
projectiles[currProj]->set_world_position_y(player->get_y() - projectiles[currProj]->get_height() - 1);
}
and here is my collision for the left of the player:
else if (projectiles[currProj]->get_x() < player->get_x()) // left of player
{
projectiles[currProj]->set_world_position_x(player->get_x() - projectiles[currProj]->get_width());
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(vy, -vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
}
The left side collision works, the top does not and I have no idea why.
If necessary I can post the entire project somewhere.
Full collision code for player:
void Game::playerCollision()
{
if (projectiles[currProj]->bb_collision(player))
{
if (projectiles[currProj]->get_y() < player->get_y()) // top of player
{
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(-vy, vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
projectiles[currProj]->set_world_position_y(player->get_y() - projectiles[currProj]->get_height() - 1);
}
else if (projectiles[currProj]->get_y() + projectiles[currProj]->get_height() > player->get_y() + player->get_height() + 1) // bottom of player
{
projectiles[currProj]->set_world_position_y(player->get_y() + player->get_height());
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(-vy, vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
}
else if (projectiles[currProj]->get_x() < player->get_x()) // left of player
{
projectiles[currProj]->set_world_position_x(player->get_x() - projectiles[currProj]->get_width());
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(vy, -vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
}
else if (projectiles[currProj]->get_x() > player->get_x()) // right of player
{
projectiles[currProj]->set_world_position_x(player->get_x() + player->get_width());
float vx = cos(projectiles[currProj]->nGetAngle());
float vy = sin(projectiles[currProj]->nGetAngle());
float newAngle = atan2(vy, -vx) * 180 / 3.14;
projectiles[currProj]->nSetAngle(newAngle);
}
}
}

Answer 1

I think your collision detection is not sufficient. without knowing your representation in detail
you do not check where the projectile (pr) came from. a collision top left within the player (pl) might have entered through the top or from the left
you do not bounce the pr immediately, you just alter the direction. depending on the entry depth it might not be able to exit with the next iteration. this happens especially on the top where the pr accelerates downwards but slows down upwards.
so you must
detect the entry surface (determines angle)
and most important rebounce immediately