Planet Gravity

[Sammy6200]

How would it be possible to make gravity attract towords the center of a giant sphere to simulate a planet with LE?

And also, would it be possible to create some sort of event horizon around the sphere that makes the gravity attract when close enough, so it would be possible to create multiple "planets" who all have gravity?

[Canardia]

It's quite easy, you just need to loop through all physics bodies and add a force to them in direction of the nearest/biggest gravity center.

[Sammy6200]

What functions will allow me to do so?

[Canardia]

ForEachEntityDo(), TFormVec() and AddBodyForce().

[Sammy6200]

i dont really understand how to use TFormVector().

 

TVec3 TFormVector(TVec3 &vector, TEntity src, TEntity dst)

 

What does it return? And what is the Source Entity and the Destination Entity?

[Sammy6200]

I did this:

 

#include "engine.h"

#include <iostream>

 

int main( int argn, char* argv[] )

{

Initialize() ;

RegisterAbstractPath("C:/Users/Sammy/Desktop/Leadwerks SDK");

SetAppTitle( "New" ) ;

Graphics( 800, 500 ) ;

AFilter() ;

TFilter() ;

 

TWorld world;

TBuffer gbuffer;

TCamera camera;

TMesh mesh;

TBody body;

TMesh mesh2;

TBody body2;

TLight light;

TMaterial material;

 

world = CreateWorld() ;

if (!world) {

MessageBoxA(0,"Error","Failed to create world.",0);

return Terminate();

}

 

gbuffer=CreateBuffer(GraphicsWidth(),GraphicsHeight(),BUFFER_COLOR|BUFFER_DEPTH|BUFFER_NORMAL);

 

camera=CreateCamera();

PositionEntity(camera,Vec3(0,0,-2));

 

material=LoadMaterial("abstract::cobblestones.mat");

 

mesh=CreateSphere(16);

body=CreateBodySphere();

EntityParent(mesh,body);

PaintEntity(mesh,material);

SetBodyMass(body,1);

EntityType(body,1);

PositionEntity(body,Vec3(0.7,0.5,0.3));

 

mesh2=CreateSphere(16);

body2=CreateBodySphere();

EntityParent(mesh2,body2);

PaintEntity(mesh2,material);

EntityType(body2,1);

PositionEntity(body2,Vec3(-0.7,0,0));

 

DebugPhysics(1);

 

 

light=CreateDirectionalLight();

RotateEntity(light,Vec3(45,45,45));

 

Collisions(1,1,1);

SetWorldGravity(Vec3(0,0,0));

 

TVec3 vector = Vec3(0,0,0);

std::string vinfo;

 

// Game loop

while( !KeyHit() && !AppTerminate() )

{

vector = TFormVector(Vec3(-2,0,0),body,body2);

 

// Update timing and world

UpdateAppTime();

UpdateWorld(AppSpeed()) ;

 

// Render

SetBuffer(gbuffer);

RenderWorld();

SetBuffer(BackBuffer());

RenderLights(gbuffer);

 

AddBodyForce(body,vector,1);

 

// Send to screen

Flip(0) ;

}

 

// Done

return Terminate() ;

}

 

 

It kinda seems to create an gravitation towords the one sphere.

[Canardia]

The only use I know for TFormVector is to rotate a vector so that it has the same rotation as some entity.

So to use it for gravity force, you point a pivot from an object to the gravity center, and then use TFormVector to get that rotation, so you can use it as force vector:

PointEntity( pivot, gravitycenter );    // pivot is parented to the object
TFormVector( &force, pivot, NULL);
AddBodyForce( object, force );

[Ending Credits]

Remember to divide the Force by the square of the distance from the centre of gravity if you want to make it realistic.

 

Fortunately the distance squared is simply the the sum of the squares of the difference in x, y and z. i.e (x₁ - x₂)² + (y₁ - y₂)² + (z₁ - z₂)²

[Sammy6200]

I still can't figure out how to do it

[Sammy6200]

I got an idea. Can anyone tell me how to get the position of an object? Is there any "GetPosition()" function, that can return the position of a body?

[Gilmer]

Yes, the EntityPosition(). You can also do this:

 

TVec3 planetpos = EntityPosition(planet);
TVec3 objpos = EntityPostion(obj);

//x
while(objpos.x<planetpos.x){
  MoveEntity(obj,Vec3(-1,0,0);
}
while(objpos.x>planetpos.x){
  MoveEntity(obj,Vec3(1,0,0);
}
//y
while(objpos.y<planetpos.y){
  MoveEntity(obj,Vec3(0,-1,0);
}
while(objpos.y>planetpos.y){
  MoveEntity(obj,Vec3(0,1,0);
}
//z
while(objpos.z<planetpos.z){
  MoveEntity(obj,Vec3(0,0,-1);
}
while(objpos.z>planetpos.z){
  MoveEntity(obj,Vec3(0,0,1);
}

 

not a good solution, but it can work.

[Sammy6200]

Thanks!

[Sammy6200]

My solution was this:

#include "engine.h"

#include <iostream>

#include <cmath>

 

int main( int argn, char* argv[] )

{

Initialize() ;

RegisterAbstractPath("C:/Users/Sammy/Desktop/Leadwerks SDK");

SetAppTitle( "New" ) ;

Graphics( 800, 500 ) ;

AFilter() ;

TFilter() ;

 

TWorld world;

TBuffer gbuffer;

TCamera camera;

TMesh mesh;

TBody body;

TMesh mesh2;

TBody body2;

TLight light;

TMaterial material;

 

world = CreateWorld() ;

if (!world) {

MessageBoxA(0,"Error","Failed to create world.",0);

return Terminate();

}

 

gbuffer=CreateBuffer(GraphicsWidth(),GraphicsHeight(),BUFFER_COLOR|BUFFER_DEPTH|BUFFER_NORMAL);

 

camera=CreateCamera();

PositionEntity(camera,Vec3(0,0,-2));

 

mesh=CreateSphere(16);

body=CreateBodySphere();

EntityParent(mesh,body);

SetBodyMass(body,1);

EntityType(body,1);

PositionEntity(body,Vec3(-0.8,0,0));

 

mesh2=CreateSphere(16);

body2=CreateBodySphere();

EntityParent(mesh2,body2);

SetBodyMass(body2,1);

EntityType(body2,1);

PositionEntity(body2,Vec3(0.2,0,0));

 

DebugPhysics(1);

 

light=CreateDirectionalLight();

RotateEntity(light,Vec3(45,45,45));

 

Collisions(1,1,1);

SetWorldGravity(Vec3(0,0,0));

 

TVec3 b1Vec = Vec3(0,0,0);

TVec3 b2Vec = Vec3(0,0,0);

TVec3 fVec = Vec3(0,0,0);

 

// Game loop

while( !KeyHit() && !AppTerminate() )

{

 

b1Vec = EntityPosition(body);

b2Vec = EntityPosition(body2);

 

fVec = Vec3((b1Vec.X - b2Vec.X)*(-1), (b1Vec.Y - b2Vec.Y)*(-1), (b1Vec.Z - b2Vec.Z)*(-1));

 

AddBodyForce(body,fVec);

 

 

if(KeyDown(KEY_UP))

{

AddBodyForce(body,Vec3(0,10,0));

}

 

if(KeyDown(KEY_DOWN))

{

AddBodyForce(body,Vec3(0,-10,0));

}

 

// Update timing and world

UpdateAppTime();

UpdateWorld(AppSpeed()) ;

 

// Render

SetBuffer(gbuffer);

RenderWorld();

SetBuffer(BackBuffer());

RenderLights(gbuffer);

 

// Send to screen

Flip(0) ;

}

 

// Done

return Terminate() ;

}

 

 

And it works perfectly!