移动对象帮助

Question

I want to know how is it possible,I could have an Object drawn at a certain point and move to the point that is touched on the screen. I am trying to use it for my game where when the user touches on the screen, the gun fires from the position of the player, but the player is stationary.

Thanks in advance.

PS

Is there a visual graphic of some sort that shows where every plot is on android.

Answer 1

I don't know what kind of library you're using to draw all of your things, but that basically doesn't matter since you only need to know two things in order to do this:

Without going into specifics on vector geometry:

1. You need to calculate the direction (x and y component) that the projectile moves in depending on your mouses position. You get this direction by simply subtracting the position of the mouse from the position of the player:

//x component of direction
float direction_x = mousePosition.x - playerPosition.x;
//y component of direction
float direction_y = mousePosition.y - playerPosition.y;

In order to just get a direction instead of adding a velocity component to this vector, you need to normalize it (so it has a length of 1):

float length =(float) Math.sqrt(direction_x*direction_x + direction_y*direction_y);
direction_x /= length;
direction_y /= length;

You then need to update the projectiles position by adding the direction_x and direction_y components to it, multiplied by the speed that you want the projectile to have (This process is called linear interpolation, by the way):

projectile_x += direction_x*speed;
projectile_y += direction_y*speed;

If you have some way of measuring the time between two frames, the speed variable should depend on the elapsed time between those frames, in order to create smooth movements on different platforms.