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Posted 12 April 2013 - 11:02 PM

Hi guys,

I'm still really not sure about how to implement jumping and gravity:

float3 position(0,0,0;
float3 velocity(0,0,0);

// this sums the forces
float3 sumForces()
{
float gravity=-4.0f;
return float3(0,gravity,0);
}

// this gets called every frame
void update(float dt)
{
// mass = 1 so acceleration = forces
float3 acceleration=sumForces();

position += velocity*dt;
velocity += acceleration*dt;
}

// this gets called when controller input changed
void onInput()
{
if(button_pressed){
// add jump but to what ?
forces.y=10.0f;
}
}


What do I do when the button is pressed for a jump ? I think I should add a positive y-value to the forces but where ? It has to go away after a second or two.

And my velocity y-value will continually decrease because of gravity so I have to clamp that to a lower limit, but what should that be ? Shouldn't my guy go faster and faster the deeper he falls ?

Thanks.

Posted 12 April 2013 - 11:00 PM

Hi guys,

I'm still really not sure about how to implement jumping and gravity:

float3 position(0,0,0;
float3 velocity(0,0,0);

// this sums the forces
float3 sumForces()
{
float gravity=-4.0f;
return float3(0,gravity,0);
}

// this gets called every frame
void update(float dt)
{
// mass = 1 so acceleration = forces
float3 acceleration=sumForces();

position += velocity*dt;
velocity += acceleration*dt;
}

// this gets called when controller input changed
void onInput()
{
if(button_pressed){
// add jump but to what ?
forces.y=10.0f;
}
}


What do I do when the button is pressed for a jump ? I think I should add it to the forces but where ? It has to go away after a second or two.

And my velocity y-value will continually decrease because of gravity so I have to clamp that to a lower limit, but what should that be ? Shouldn't my guy go faster and faster the deeper he falls ?

Thanks.

Posted 12 April 2013 - 08:04 PM

Hi guys,

I'm still really not sure about something. I'm using a simple 'vehicle' model:

force = truncate (sum_of_forces, max_force);
acceleration = force; (since mass = 1)
velocity = truncate (velocity + acceleration, max_speed);
position = position + velocity;

What I don't fully get is handling it for each frame. Do I maintain the acceleration and velocity in actual values or in units per second, like this (notice the difference in the calculations):

void updateFrame(float t)
{
// in units per second
acceleration += truncate(forces,max_force);
velocity += acceleration;
position += velocity*t;

// or in actual units
acceleration += truncate(forces,max_force)*t;
velocity += acceleration*t;
position += velocity;
}


For basic movement I can't see a difference but now I'm adding jumping and gravity and am a little confused.

Thanks.

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