Need help with my jump physics code

Seeker2002

I need some help with the jump physics example I found on the web. The following code makes my character go up and down, but I have to press and hold down the arrow-up key on my keyboard. I want my character to complete a full jump cycle without having to hold the arrow-up key down. I want to be able to press down on the key once and release to do a complete jump. Do I need to somehow include a do while loop? :confused Thanks! :)

bool jumping;
const float step = 0.05f; // how much the player will move per frame when jumping
const float limit = 1.0f; // the maximum height the player can reach while jumping

if (GetAsyncKeyState(VK_UP)== TRUE) // jump key
{

static float jump = 0.0f;
static float strength = limit;

if(jumping){

jump += step;

if(jump <= limit){

strength -= step;

player.y += (step * strength);
}
else{
strength += step;

// detect if moving the player down would put him below the ground
// 0.0f is assumed to be the ground here

if(player.y - (step * strength) <= 0.0f)){
player.y = 0.0f;

jumping = false; // the player has landed
jump = 0.0f;
strength = limit; // reset the strength
}

else{
player.y -= (step * strength);
}
}
}
// rest of rendering...
}

Chuck OToole

OK, this code is posted "out of context" (it simply starts with the "if" statement, not how you got there). A reasonable assumption given your problem statement is that this code is run as part of an "OnChar()" or other event *caused* by your holding a key down. If that's the case, and you want to convert this to code that runs in a loop, you need to address two things. 1) what event starts the "jumping"? 2) what event stops the "jumping"? Clearly, right now event 1) is you holding down a key, event 2) is when you let it go. Letting the key go is *not* an event, it's the absence of a key_down event. You'll need to figure out the "stop" event first.

Seeker2002

Hi Chuck O'Toole, thanks for the quick reply. These are global variables:

bool jumping;
const float step = 0.05f; // how much the player will move per frame when jumping
const float limit = 1.0f; // the maximum height the player can reach while jumping

And the rest of the code below is contained inside of my game rendering function. The jump code works when I press the arrow-key, it just does't work correctly.

BOOL StartGame ()
{
if (GetAsyncKeyState(VK_UP)== TRUE) // jump key
{

static float jump = 0.0f;
static float strength = limit;

if(jumping){

jump += step;

if(jump <= limit){

strength -= step;

player.y += (step * strength);
}
else{
strength += step;

// detect if moving the player down would put him below the ground
// 0.0f is assumed to be the ground here

if(player.y - (step * strength) <= 0.0f)){
player.y = 0.0f;

jumping = false; // the player has landed
jump = 0.0f;
strength = limit; // reset the strength
}

else{
player.y -= (step * strength);
}
}
}
// rest of rendering...
return TRUE;
}

CPallini

If I got you: use a tristate variable instead of a boolean, say jump_state.

enum JumpState
{
JS_IDLE,
JS_START,
JS_JUMPING
};

//..

jump_state = JS_IDLE; // initialization

// ...

// main loop
if (GetAsyncKeyState(VK_UP) == TRUE)
if (jump_state == JS_IDLE)
jump_state = JS_START;
else
if (jump_state == JS_START)
jump_state == JS_JUMPING;
//...

if ( jump_state == JUMPING)
{
// here do a step of jumping movement
if ( landed )
jump_state == JS_IDLE;
}

Veni, vidi, vici.

Chuck OToole

Nice idea

CPallini

Thank you.

Veni, vidi, vici.

Seeker2002

Hey guys, thanks again for y'alls help. I got it working now. You guys are great! :)

CPallini

You are welcome.

Veni, vidi, vici.