2d game physics/programming quesiton... C++/SDL

AdrenalineJunky · 2009-06-02 11:12:42

For the last couple of days i've been trying to learn C++/SDL by wprking on making a 2d platformer.

the basics of what i'm working with (stripped down to just the relevant components)

game loop

while( SDL_PollEvent( &event ) )
{
myHero.handle_input();
//If the user has Xed out the window
if( event.type == SDL_QUIT )
{
//Quit the program
quit = true;
}
}

myHero.move( blahbox );

//Set the camera
myHero.set_camera();

handle_input()

if( event.type == SDL_KEYDOWN )
{

if( SDLK_LEFT ) { xForce -= HERO_WIDTH / 2; }

if( SDLK_RIGHT ){ xForce += HERO_WIDTH / 2; }

}
else if( event.type == SDL_KEYUP )
{

if( SDLK_LEFT ) { xForce = 0; }
if( SDLK_RIGHT ) { xForce = 0; }

}

move()

void Hero::move(SDL_Rect blahbox)
{
//Move the dot left or right
if( xForce != 0 ) { xAcc = xForce / HERO_MASS; }
if( xForce == 0 ) { xVel = xAcc = 0; }
xVel = xVel + xAcc;
box.x = box.x + xVel;

//If the dot went too far to the left or right or touched a wall
if( ( box.x < 0 ) || ( box.x + HERO_WIDTH > LEVEL_WIDTH ) || check_collision( box, blahbox) )
{
//move back
box.x = box.x - xVel;
}

}

what i was going for is force is applied when a key is pressed,

accelleration = Force / Mass
Velocity = Velocity + Accelleration
etc...

when no force is being applied, set velocity and accelleration to 0

now, i know thats a little unrealistic, i was going to try to set it to slow down etc later, but i can't get this working.

for whatever reason, when i lift the key my guy just keeps cruising along at whatever speed he was going before...

anybody know what i'm doing wrong?

Last edited by AdrenalineJunky (2009-06-02 11:13:50)

AdrenalineJunky · 2009-06-02 13:05:37

figured out my problem, i saved a backup copy and didn't realize i was working on the backup copy.....

so i kept recompiling my old code without any changes i was making.

after compiling the correct code it does exactly what i thought it should....

whoops · 2009-06-02 13:46:55

Great, I'm not alone!

Little trick on the side: try to make more typos. You already know some-thing's wrong when you don't get an error message trying the program for the first time after a major addition/change!

AdrenalineJunky · 2009-06-02 13:54:33

^^^ thats actually what made me realise what was going on.

all the sudden it dawned on me... i haven't had a compiler error in a while... something can't be right

Runiq · 2009-06-02 14:12:26

And here's another (forum-related) trick: Try putting [ code ] and [ /code ] tags around your code, makes it more readable.

AdrenalineJunky · 2009-06-02 14:46:12

thanks for the tip ^^

ok, so i have another question...

i put in a simple method of checking if the character is moving vertically and disable jumping if he is ( i should probably make it check if he is touching the ground... but i'll get there )

and that works - if the character is in the air and i press the jump key he doesn't jump again. problem is if i hold the jump key in the first place he will continue going up till he reaches the top of the level.

basically i have this:

    

if( yForce != 0 ) { yAcc = yForce / HERO_MASS; } 
if( yForce == 0 ) { yAcc = 3;  } // for gravity
if( yVel >= 10 ){ yVel = 10; } 
if( yVel <= -10 ){yVel = -10;}
yVel =  yVel + yAcc;


oldbox = newbox;
//Move the dot up or down
newbox = box.y = box.y + yVel;
if (newbox == oldbox) {jumping = false;}
else { jumping = true; }

switch( event.key.keysym.sym )
{
    case SDLK_UP: if( jumping == false ) { yForce -= 20; break; }
    if( jumping == true ){ yForce = yForce + 3; break;} // supposed to slow down and stop vertical movement. but doesn't work.
}

Last edited by AdrenalineJunky (2009-06-02 14:46:37)

AdrenalineJunky · 2009-06-02 15:48:37

nevermind, got it figured out

Themaister · 2009-06-03 09:21:33

Heyhey Another beginner SDL/C++ coder. Me and a friend have recently started on an SDL/C++ game. A 2D-platformer too I'm a beginner when it comes to SDL/C++ though, but we have a googlecode page up at least.
http://code.google.com/p/the-escapist/
Still in consept phase though. The code is merely just some basic physics stuff (and being able to have a scrolling background (marioish)).

Next step would probably be adding collition detection with arbitary platforms around the map.

Last edited by Themaister (2009-06-03 09:38:26)

Arch Linux

#1 2009-06-02 11:12:42

2d game physics/programming quesiton... C++/SDL

#2 2009-06-02 13:05:37

Re: 2d game physics/programming quesiton... C++/SDL

#3 2009-06-02 13:46:55

Re: 2d game physics/programming quesiton... C++/SDL

#4 2009-06-02 13:54:33

Re: 2d game physics/programming quesiton... C++/SDL

#5 2009-06-02 14:12:26

Re: 2d game physics/programming quesiton... C++/SDL

#6 2009-06-02 14:46:12

Re: 2d game physics/programming quesiton... C++/SDL

#7 2009-06-02 15:48:37

Re: 2d game physics/programming quesiton... C++/SDL

#8 2009-06-03 09:21:33

Re: 2d game physics/programming quesiton... C++/SDL

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