simple help

[blanius]

I have a projectile with x and y velocities. I have a starting x,y and a target x,y isn't there a simple formula to set the x and y velocities to move it to the target x and y? Ideally this would be a calculation for velocity.y for a given velcoity.x,target.x and target.y

[ericlin]

Long time ago, I ever replied similar thread in actionscript forum.

The calculation is not simple.

Anyway, here is the zip file , I posted. I have forgot the equation formula.

[ericlin]

Ideally this would be a calculation for velocity.y for a given velcoity.x,target.x and target.y

Wow, if the velocity x, target.x and target.y are know, the equation to get initial velocity y is simple.

t=(target.x-origin.x)/vx;

then
target.y=origin.y+vy*t+(g*t*t)/2;

so, vy=((target.y-origin.y)-(g*t*t/2))/t;

[blanius]

Originally posted by ericlin
Wow, if the velocity x, target.x and target.y are know, the equation to get initial velocity y is simple.

t=(target.x-origin.x)/vx;

then
target.y=origin.y+vy*t+(g*t*t)/2;

so, vy=((target.y-origin.y)-(g*t*t/2))/t;

I figured it was simple for someone that knows their math.

Help me here what is g and how do I get it. If this is gravity, I don't need any gravity effect so what would I use here? I assume vx is velocity.x and vy is velocity.y for my projectile.

[ericlin]

Yes, I mean velocity.x and velocity.y;

g is gravity. Or, we can call it "acceleration". Because you want a "projectile" curve, there must be an "acceleration". In real world, that is "gravity - 0.98". In flash world, you can give it any value you like. If you give g a large positive value, the projectile curve is sharp. If you give g a small value, the projectile curve will be nearly a straight line. If you give g a negative value, the curve will goes up.

If you omit g, then it is not projectile. It shoot the target directly.

Then velocity.y=(target.y-origin.y)/t;

[blanius]

Thanks this is now working. Only had to make one minor adjustment to check if vx needed to be positive or negative and it works great thanks tons!!