So i'm trying to make my first game on android. The thing is i have a small moving ball and i want it to bounce from a line that i drew. For that i need to find if the x,y of the ball are also coordinates of one dot from the line. I tried to implement these equations about lines x=a1 + t*u1 y=a2 + t*u2 = (x-a1)/u1=(y-a2)/u2 (t=t which has to be if the point is on the line) where x and y are the coordinates im testing, dot[a1,a2] is a dot that is on the line and u(u1,u2) is the vector of the line. heres the code: public boolean Collided() { float u1 =Math.abs(Math.round(begin_X)-Math.round(end_X)); float u2 =Math.abs(Math.round(begin_Y)-Math.round(end_Y)); float t_x =Math.round((elect_X - begin_X)/u1); float t_y =Math.round((elect_Y - begin_Y)/u2); if(t_x==t_y) { return true; } else { return false; } } points [begin_X,end_X] and [begin_Y,end_Y] are the two points from the line and [elect_X,elect_Y] are the coordinates of the ball theoreticaly it should work, but in the reality the ball most of the time just goes straigth through the line or bounces somewhere else where it shouldnt