point based gravity

[waggle]

By what method would you recommed creating gravity centred on a single point in the middle of a screen (i.e. rather than everything just being pulled down)?

The only way I can think of doing it would be to have a global array of velocity vectors (two for each object to be affected by the gravity) which would have to be updated each frame manually. Surely there's a less computationally intensive way of doing this.

[Fuzzy]

Games have been doing this for nearly 30 years; its not computationally expensive with the right technique. I'l let you think it over; reply if you find a way, or I will give you a solution tomorrow. (Sorry, I am on my way to bed!)

[DilloDude]

My method is to use the ReDir function (http://game-editor.com/forum/viewtopic.php?t=1934&highlight=redir) to change the angle, and make another function using the getangle function (included) which returns the size of the angle from A to B, which will adjust the velocity.

[waggle]

Thanks for the suggestions. Here's my code. I put this in the drawevent for the object. GravityWell is the gravity source. I did not include a mass for the object since as long as it is a tiny fraction of the mass of the "GravityWell" it is not significant to the calculations.

Yes, it's a mess but I was just trying to get some code working.

Oh, and the createactor for the object had an initial xvelocity and yvelocity (otherwise the object would simply fall directly into the gravity well).


double d_Distance;
double d_GravityConst;

double d_Direction;
double d_deltaXcomponent;
double d_deltaYcomponent;
double d_Mass;
double d_TimeConst;
d_GravityConst = 10;
d_TimeConst = 10;
d_Mass = 10;


d_Distance = distance(xscreen, yscreen, GravityWell.xscreen, GravityWell.yscreen);
d_Direction= direction(GravityWell.xscreen, GravityWell.yscreen, xscreen, yscreen );
AngleNumber.textNumber = d_Direction;
// Convert Direction to radians from degrees
d_Direction = 2 * 3.14159265 * (d_Direction/360);

XVelNumber.textNumber=d_deltaXcomponent= -1*
(cos(d_Direction)*d_GravityConst*d_Mass*d_TimeConst) /( d_Distance*d_Distance);
YVelNumber.textNumber= d_deltaYcomponent=
(sin(d_Direction)*d_GravityConst*d_Mass*d_TimeConst) /( d_Distance*d_Distance);


xvelocity +=d_deltaXcomponent;
yvelocity +=d_deltaYcomponent;

[Fuzzy]

What you can do is have it run through say 10 or even 100 possible distances in global code, storing each result to a array, and when you do the draw, just take the distance and look it up in the array and get your falling speed.

gravity[distance]

or something of the like. This will save you a good deal of computation each draw, and should make your game run faster and smoother.