Question about making a gravity game

[LaZ3R]

I want to create a simple game where you choose the angle to launch the ball, along with the speed of it, and it must use the gravitational field of a planet in order to push itself around the planet and into the target.

It's basically like that flash game that was made a while ago

I'm just having a bit of trouble thinking about how to start this. I was thinking of implementing Fg = GMm / r^2, but don't know if it would really help me in this case . Any suggestions would be awesome

[Ultrahex]

This is actually one of the examples that i think is in the Turing Example Programs.

But yes you are correct you could use that formula and measure the distance, just remember you are working with pixels, so your distances of measurement shouldn't be as ridiculous as in the constants given in that formula, but the ratios (as in formula structure) should be roughly the same if not the same.

[LaZ3R]

The example program for this gravity idea is terrible. It's so unorganized and hard to follow. Partly why I never use those example programs. Better to learn for myself, easier to understand an individuals own code

Thanks though. I got it working in 20 lines or so Need to improve it now

[LaZ3R]

Only problem I'm having right now is making the ball move at a certain angle instead of going straight into the other ball at an increasing acceleration.

Fg := (G * m1 * m2) / (Math.Distance (x1, y1, x2, y2)) ** 2

Basically my formula for now and
x1 += (x2 - x1) * Fg
y1 += (y2 - y1) * Fg

is what I used to determine the new position of the ball each time through the loop. How can I manipulate the formula so I can choose an initial angle so it can kind of have an orbit effect around the other ball?

[LaZ3R]

I'm kind of figuring out how to get it working half of how I want it

I'll figure it out, just need to clear my mind

Thanks.

[Saad]

Ok, so you know that Fg = GMm / r^2 gives a force, now F = ma so then acceleration is F/m. This gives us the magnitude of acceleration, so now we just have to split it into its vector components.

Ax = cos(theta) * |A|
Ax = sin(theta) * |A|

Where theta is the angle between the two balls.

[Ultrahex]

It appears (from how i understand what you just posted), that your physics is incorrectly done.

An initial angle and such would be done by setting an initial velocity... BTW the Force Of Gravity should not act on the location, it should act on the velocity!

Acceleration Changes Velocity
Velocity Changes Position.

For Example For Free Fall Gravity its Fg = mg , where Fg is the force of gravity, m is the mass, and g is the acceleration due to gravity.

lets assume our mass is 1kg, and gravity is 9.8m/s^2 like usual on earth.
also assume our initial position is x=0, y= 10, and velocity = 0 (for simplicity).

After 1 Second, velocity = 9.8m/sec down, x=0 still, y=0.5*9.8m/sec
After 2 Second, velocity = 2*9.8m/sec down, x=0 still, y=0.5*9.8*2^2=2*9.8
After 3 Second, velocity = 3*9.8m/sec down, x=0 still, y=0.5*9.8*3^2=(9/2)*9.8
....

thus... after each moment in time, our velocity increase by Fg since Fg is constant its just going up by 9.8m/sec each time. However since you are using Fg = GMm / r^2, Fg is not constant and needs to be calculated at each point in time before adding to velocity.

The position is affected by its velocity, which you can do simple ways (as in just adding your velocity to its position, or actually calculate it correctly .

[LaZ3R]

LOL, I didn't realize I put Fg in there. Kind of trying to skip a few steps I see

I'm half asleep right now, that would explain a lot

Saad's method should work just perfectly actually, Think the fact that we are currently doing some weird stuff in Electrostatics in Physics is screwing me over

[LaZ3R]

Thanks guys

[Sean]

I'm actually looking for a gravity script, been working on one for a Mario game that me and Gooie were working on.

Any idea how to do it properly, and get the character to jump and come down?

[Nick]

try if ground (or chary = y of ground or whatdotcolp(charx,chary - 1) = ground color) then jump proc

your jump procedure will be like your regular loop except it dissallows the chracter to jump again and y velocity increases until max height is reached then it dereases until your chra hits the ground

hope that helps

[Ultrahex]

Not to insult you momop or anything, but in order for correct jumping what you would do is something similar what you said for collision detection with ground. However for proper gravity jumping with jump procedure you would have an initial velocity speed upwards on the jump and then gravity would pull the character down.

I will implement something like this just to show the difference.

[Nick]

i think i know what you mean

what I said:

the character raises at a constant speed then falls immediatly at the same speed

what you said:

the character raises at a speed relitive to gravity slows at the height then falls at the speed relitive once again to gravity

[Ultrahex]

Precisely, yours assumes constant velocity, mine is assuming constant acceleration which looks more realistic, for code example:

If you do not see the difference,
In assuming constant velocity, the character moves up and down at same speed
In assuming constant gravity, the gravity of the things around it are constant (such as each pulling down), thus the character moves up and down with different speeds and reaches 0 velocity at the top of the jump and then becomes negative to mean downwards direction.

keys:
r is change realistic
a,d are move left, move right
w is jump

Turing:

% Type Declarations type point :     record         x : real         y : real     end record type obj :     record         v : point % Velocity         s : point % Position         isJump : boolean     end record % Variables var realistic : boolean := true const g := 9.8 var player : obj player.isJump := false player.v.x := 0 player.v.y := 0 player.s.x := 50 player.s.y := 0 var keys : array char of boolean % Procedures fcn applyGravity (o : obj) : obj     var a : obj := o     if (realistic) then         a.v.y -= g         a.s.y += a.v.y     else         if (a.isJump) then             if (a.s.y <= 145) then                 a.v.y += g                 a.s.y += a.v.y             else                 a.v.y -= g                 a.s.y += a.v.y             end if         end if     end if     result a end applyGravity proc gameLoop ()     loop         Draw.FillBox (round (player.s.x), round (player.s.y), round (player.s.x + 10), round (player.s.y + 10), brightred)         put "Realistic: ", realistic         put "Jumping: ", player.isJump         put "Vel (x,y): (", player.v.x, ",", player.v.y, ")"         put "Pos (x,y): (", player.s.x, ",", player.s.y, ")"         Input.KeyDown (keys)         if keys ('r') then             realistic := (not realistic)         end if         if keys ('a') then % Move Left             player.s.x -= 15         end if         if keys ('d') then % Move Right             player.s.x += 15         end if         if keys ('w') then % Jump             if (not player.isJump) then                 player.isJump := true                 if (realistic) then                     player.v.y += 74                 end if             end if         end if         player := applyGravity (player)         if (player.s.y <= 0) then             player.s.y := 0             player.v.y := 0             player.isJump := false         end if         View.Update ()         delay (100)         cls         exit when keys ('x')     end loop end gameLoop % Start Program View.Set ("offscreenonly") gameLoop ()